CA2181457C - Terrain elevation path manager - Google Patents
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Abstract
A terrain profile for executing terrain following flight is generated using a minimal volume of digital terrain elevation data (DTED) information. By limiting the amount of information considered in generating the terrain profile, the computational time and resource requirements for terrain profile generation are reduced, but without comprising the integrity of the terrain profile generated. The sample region is limited by limiting the width of sample regions according to expected use including most likely terrain following flight command data, potential unexpected flight path deviation, and long range terrain following flight data.
Description
TERRAIN ELEVATION PATH MANAGER
BACKGROUND OF THE INVENTION
The present iuveation relates generally to terrain following aircxaft control, and more particularly to a method for accessiag~and utilizing ten~ain elevation data in the context of terrain following flight.
To minimize above ground elevation, and therefore urinimize visibility sad 1o winerability to ground based detection and attack, military aircraft often execute terzain following flight. 'Terrain following flight generally maintains a gives elevation above ground level independent of actual elevation above sea level. In other words, the aircraft follows the ground contour at a subataatially faced elevation above the Bound and maneuvers according to prevailing ground contour along a gives flight Bath. The actual above ground level elevation may increase to establish a suitable climb angle to char an upcoming high elevation Terrain feature.
The gcnerai algorithm applied to flight foiloaiing terrain is to select the tallest terrain feature lying along and near the flight path. The aircraft altitude and attitude vector are referenced to determine whether or not an upcoming terrain feature will be Z 0 cleared. If necessary, the terrain following algorithm requires that the aircraft eater a suitable climb angle to clear any upcoming terrain features. Otherwise, the algorithm would maintain a substantially consistrent above grownd elevation according do a given terrain profile data structure.
A,s used herein, the term "terra'sn profile" shall refer to a data struuure representing terrain along a given flight path. A terrain following algorithm uses the terrain profile data struc4rne to execute terrain following flight slung the designated flight path. A terrain proFile may be tlwught of generally as a terrain cfosa-sectioaat, elevational contour, e.g., as taken through a vertical plane containing the flight path, but must account for terrain conditions near the designated Might path. For examples 3 0 for a given point along the flight path, the highest elevation point laterauy outward on either side a given distance is assigned as the terrain proFle elevation at the gives point. This produces a conservative, i.e., safe, elevation contour in the terrain profile.
Most terrain follov~~ing applications use radar and/or radar sensor data to generate a terrain profile along a predicted flight path of the airczaft. The predicted flight path is generally based on the current aircraft attitude and velocity.
Terrain following flight is preferably executed, however, with limited or no active sensor data because aciive sensor emissions make the aircraft visible to threat installations at greater dis'~ances. Using active sensors, especially at high oawer, com,~romises covert missions because the aircraft can be detected at long distances by hostile forces. If active sensors are to be used, such sensors are preferably used at low power settings to minimize detectable emissions and allow only short range detection by hostile forces.
Unfortunately, terrain following fligi~t requires more distant terra.ia-iaformation, typically exposing the aircraft to detection if generated using long range high power active sensors. Furthermore, active sensor data has its limitations. Sensor data alone cannot see behind hills or around corners. Sensors can only "guess" where to gather te~ain data. in generating a terrain profile.
1S Digital terrain elevation data represents surface elevation at discrete "data posts." Each data post has a surface location or address, e.g. latitude and longitude, and an associated elevation, e.g. ;eiative to sea level. Thus, a simple form of a DTED
database would deliver a sealer elevation datum in response to longitude and latitude address input, h4ore complicated DTE3~ databases have been developed far certain zo applications. p'or example U.S. Patent Na. 4,899,?92 issued February 6, 1990 to J. F.
Dawson and E. W. Ronish shows a tessellation method for cxeating a spherical database by warping a digztal map, including digital terrain elevation data, by longitude and IatiW de parameters.
DTED database systems are used in flight mission computer systems and flight
BACKGROUND OF THE INVENTION
The present iuveation relates generally to terrain following aircxaft control, and more particularly to a method for accessiag~and utilizing ten~ain elevation data in the context of terrain following flight.
To minimize above ground elevation, and therefore urinimize visibility sad 1o winerability to ground based detection and attack, military aircraft often execute terzain following flight. 'Terrain following flight generally maintains a gives elevation above ground level independent of actual elevation above sea level. In other words, the aircraft follows the ground contour at a subataatially faced elevation above the Bound and maneuvers according to prevailing ground contour along a gives flight Bath. The actual above ground level elevation may increase to establish a suitable climb angle to char an upcoming high elevation Terrain feature.
The gcnerai algorithm applied to flight foiloaiing terrain is to select the tallest terrain feature lying along and near the flight path. The aircraft altitude and attitude vector are referenced to determine whether or not an upcoming terrain feature will be Z 0 cleared. If necessary, the terrain following algorithm requires that the aircraft eater a suitable climb angle to clear any upcoming terrain features. Otherwise, the algorithm would maintain a substantially consistrent above grownd elevation according do a given terrain profile data structure.
A,s used herein, the term "terra'sn profile" shall refer to a data struuure representing terrain along a given flight path. A terrain following algorithm uses the terrain profile data struc4rne to execute terrain following flight slung the designated flight path. A terrain proFile may be tlwught of generally as a terrain cfosa-sectioaat, elevational contour, e.g., as taken through a vertical plane containing the flight path, but must account for terrain conditions near the designated Might path. For examples 3 0 for a given point along the flight path, the highest elevation point laterauy outward on either side a given distance is assigned as the terrain proFle elevation at the gives point. This produces a conservative, i.e., safe, elevation contour in the terrain profile.
Most terrain follov~~ing applications use radar and/or radar sensor data to generate a terrain profile along a predicted flight path of the airczaft. The predicted flight path is generally based on the current aircraft attitude and velocity.
Terrain following flight is preferably executed, however, with limited or no active sensor data because aciive sensor emissions make the aircraft visible to threat installations at greater dis'~ances. Using active sensors, especially at high oawer, com,~romises covert missions because the aircraft can be detected at long distances by hostile forces. If active sensors are to be used, such sensors are preferably used at low power settings to minimize detectable emissions and allow only short range detection by hostile forces.
Unfortunately, terrain following fligi~t requires more distant terra.ia-iaformation, typically exposing the aircraft to detection if generated using long range high power active sensors. Furthermore, active sensor data has its limitations. Sensor data alone cannot see behind hills or around corners. Sensors can only "guess" where to gather te~ain data. in generating a terrain profile.
1S Digital terrain elevation data represents surface elevation at discrete "data posts." Each data post has a surface location or address, e.g. latitude and longitude, and an associated elevation, e.g. ;eiative to sea level. Thus, a simple form of a DTED
database would deliver a sealer elevation datum in response to longitude and latitude address input, h4ore complicated DTE3~ databases have been developed far certain zo applications. p'or example U.S. Patent Na. 4,899,?92 issued February 6, 1990 to J. F.
Dawson and E. W. Ronish shows a tessellation method for cxeating a spherical database by warping a digztal map, including digital terrain elevation data, by longitude and IatiW de parameters.
DTED database systems are used in flight mission computer systems and flight
2 5 planning strategy in military applications aid iu, for example, covert sad evasive flight operations. As used in mission computer systems, a DTED database can aid a pilot in trine-critical maneuvers such as terrain following flight or in selecting routes ~ H,sive with respect to a given threat position. Such threat positions may be known in advance, or detected while is flight. The computation speed resluired in accessing sad
3 0 calculating mutes or alternatives based on DT~D can be vitally c:itical, especially fQr repeated computations required to keep a pilot fully appraised of current teixain _;_ conditions and route al;ernatives. Thus, improvements in mettzods of accessing DTED
and comQutatioas based on extracted DTED are not sirnpiy improvements in computational elegance, but can be life-saving and critical to mu.ssion success.
Terzain profiles have been built by extracting a massive volume of DTED data with reference to a designated flight Bath. As may be appreciated, each data sample Liken from the DTED database far consideration is generating the terrain profile requires a given amount of processing time. The data extracted from the DTED
database for generating the terrain profile corresponded to data posts lying along a length of the fliglat path preceding aircraft position and all data posts within a given distance of that length portion, i.e, a fixed length and ~~idth region of data posts along the flight path and identified relative to current aircraft position. The terrain profile :nest provide safe, conservative information. To this end, a large volume of DTED
data has been incarpozated into terrain profiles. Unfot'tunateiy, the volume of data extracted and processed has constrained terxain profile generation, i.e., has required excess terrain profile calculation time.
Thus, prior methods of generating terrain profiles include long range active s°nsozs, but long range sensor emissions make airczaft visible at long distances. These prior art methods have included DT):.D database systems, but generating conservative terrain profiles requires massive zzumbers of DTED data points and can require 2 0 relativ ely long calculation ti me.
A relevant prior art reference is European Patent application 0 499 874, a ray-tracing algorithm method with a digital database to process only the visible surfaces in a field of view. During operation to different sets of inforaiacion are analyzed. The first is a constant width data corridor comprising a narrow and of high resolution data.
Second is a widex band of lower resolution data_ The focus of this invention is the resolution of the data in the particular corridor. , It is desirable, therefore, that terrain following flight be executed without aid of high power, long range active sensor data to avoid exposing the airc.-a~ to threat installations. It is fufther desirable that a method of producing a terrain pmfile for 3 ~ executing terrain following flight support dynamic and efficient calculation time.
SUlIr~VIARY CfF THF INV'EN"TION
In accordance with the present invention, an aircraft flight path is selected and a limited volume of DTED data points ase extracted from a DTED database to safely minimize the above wound level elevation at any given point during the terrain following flight. I~iore particularly, the DTED data points extracted from the database are takes from sample regions havimg dimension according to conditions such as time sad distance relative to the aircraft.
In accordance with a preferred embodiment of the present invention, each sample region is centered upon the selected flight path and positioned relative to the aircraft, but varies in width relative to other sample regions. Cmaerally, the wider 1o sample regions are near the aircraft, and sample regions more distaatfrom the aircraft along the selected flight path become increasing more narrow. The widest sample region corresponds to a portion of the flight path, at a given position relative to the aircraft, associated with potential aircraft flight path deviation. . Thus, additional terrain data is considered in the event of such unexpected deviation from the terrain i5 following flight path. In this manner, a relatively greater volume of DTED
data is extracted as needed. More distant terrain along the flight path is suitably evaluated, but using a lesser volume of DTED data. As a result, computational throughput and memory requirements for terrain following flight algorithms are minimized while maximizing terrain fallowi.ag performance and safety criteria.
2 o The raethod of generating a terrain profile is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation of the invention, together with further advantages and objects thereof, may best be understood by reference to the following ddcription taken with the accompanying drawings wherein like reference characters 2 5 refer to like elements.
-4a-In accordance with one aspect of this invention, there is provided a method of generating a terrain profile on an aircraft's flight mission computer system using a sample region of digital terrain elevation data which corresponds to an aircraft's position and predicted flight path, the method comprising the steps: identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands, said plurality of sample regions include, said sample regions being updated as the aircraft progresses along the flight path; and transforming said plurality of sample regions into a terrain profile, wherein a first sample region is dimensioned according to short range terrain following flight command data needed, a second sample region is dimensioned according to potential flight path deviation data needed, and a third sample region is dimensioned according to long range terrain following flight data needed; the first sample region being an intermediate volume and closest to the aircraft, the second sample region being a greatest volume and next closest to the aircraft, and the third sample region being a least volume and most distant from the aircraft; and transforming data posts of said first, second, and third sample regions into a terrain profile.
In accordance with another aspect of this invention, there is provided a method of generating a terrain profile on an aircraft's flight mission computer system using a sample region of digital terrain elevation data which corresponds to the aircraft's position and predicted flight path, the method comprising the steps:
-4b-identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands; and transforming said plurality of sample regions into a terrain profile, wherein said plurality of sample regions include: a first sample region having length and width dimensions chosen as a function of data required for execution of terrain following flight commands for terrain in a vicinity of the aircraft; a second sample region located directly under and along said flight path and in advance of said first sample region relative to said aircraft position, said second sample region having length and width dimension which are directly related to potential flight path deviations caused by unexpected events; a third sample region with a length and width determined from data required in returning to said flight path from one of said potential flight path deviating conditions; and a fourth sample region located furthest from said aircraft in relation to said first, second, and third sample regions, said fourth sample region having a minimum width dimension relative to the width dimensions of said first, second and third sample regions.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
-5.
FIG. 1 illustrates in plan. view a sample region taken from a DTED database in accordance with the present invention foc generating a terrain profile to aid in terrain following flight.
FIG. 2 illustrates a terrain profile generated frorn the sample reF.~'on of FIG 1.
DET,r'IIi.ED l?ESCRIPTIOlV OF TTr~ PREFERRED EMBODIMENT
FIG. 1 illustrates a flight Bath 10 with reference to a portion of a digital terrain elevation data (I7'f'ED~ database i2 comprising a grid of data posts 14. Each data post I~ is indicated in FIG. 1 as an "X", but no scale in data post 14 spacing is indicated nor is every data post 14 shown, DTED database 12 may take a variety of formats, but as relevant to the present invention may be taken generally as an X"Y
addressable array of data posts 1~, e.g., addressed by latitude and longitude, and providing elevation at a given location. The flight path 12 may be a flight path selected as part of a mission plan, or may be a flight path predicted dynamically as a function of the current aircraft attitude and velocity vectors. In either case, it is necessary to extract from the DTED database 12 elevation data xelaiive to flight path 10 to generate a terrain proftte in aid of terrain following flight tbesealoag.
Terrain following flight is executed in accordance with the present invention 2p by reference to the DTED database 1~ with little or no additio~aal active sensor data.
Any active sensors used would be at low power and detectable only within several nautical miles of the air~aft. It is desirable to cxecate such terrain following flight with a minimum above ground level elevation to minimize the aircra~ visibility arid vulnerability to attack from threat installations. Using a terrain profile based on DTED information, the aircraft can achieve such minimum above ground Level elevation by anricigating upcoming terrain conditions and minimizing above ground level elevation with resQect tv such anticipated terrain conditions taking into account aircraft and pilot flight capabilities and reaction times.
As may be aQpreciated, a DTED database can be huge and cornputationaily burdensome to analyze in its entirety, especially while dynamically executing terrain following flight. In accordance with the present inv ention, izowever, only a limited 2~ao5~
portion of database 12 need be extracted, i.e., sample zegion 18, for use in generating a terrain profile for executing terrain following flight. This minimizes the computation and memory requirements of such terrain following fligb~t. The sample. region includes a set of subrerions 18a-18d each selected dynamically as a function of aircraft 16 position along fight path 10.
A short-term profile subregiorl 18a exists along flight path 10 beginning at and e:rtending approximately 2 nautical miles in front of aircraft 16. 'the width of short-term profile subregion 18a may vary while in flight as a function of aircraft NAV
CEP, cross track deviation, and aircraft 16 wingspan This restricts fine adjustments l o of the terrain profile obtained to the xegion of database 12 from which most terrain following steering commands are most likely generated, i.e., the horizon,to clear is typicahy within 2 nautical males of the aircraft 16.
A first m.id-terra. profile subregion 18b, beginning at approximately 2 nautical miles in front of aircraft i6 along flight path 10 and terminating at approximately 5 nautical miles from aircraft 16, is relatively wider than that of short-term subregion I Sa. The width of mid-term subregion 18b may be a coBStant width, bat defined as a function of potential forces or conditions acting to drive the aircraft 16 off the selected or predicted flight path 10, Thus, to the extent that aircraft i6 may deviate from path 10, region 18b should be suitably wide enough to anticipate flight within this range of 2 Q potential deviation. The type of forces considered in establishing a width for mid-term subregion 18b can be generally characterized as unpredicted conditions.
Fur example, a sudden, unexpected sidewind may drive the aircraft off the flight path I0, or an unforeseen event may distrac~ the pilot and the aircraft might deviate to some r extent relative to flight path 10. Thus, in establishing the width of niid-term subregion 18b, a variety of potential path deviating conditions may be considered. Also;
the width calculation should tale into account specific information such as pilot resQonse dme to ungredicted events and the specific aircraft used, i.e., aircraft response to pilot commands, For example, a fast aircraft having relatively slow ground track response may require a relatively wider subregion 18b due to the relatively greater distance the aircraft could potentially deviate from flight path 10 due to its speed and relatively _?_ slow ground track respansc. Ia contrast, a slow, large aircraft may have fast ground track response and permit a relatively more narrow subregion 18b.
A second mid-term subrcgion 18c, beginning at approximately 5 nautical miles along flight path from aircraft 16 and terminating at approximately T nautical miles along flight path 10 relative to aircraft l6, is relatively more narrow than that of subregion 18b. It is assumed that the pilot will steer back onto path 10 is response to any path deviating forces detected in region 20 and thereby have the advantage of early consideration of the subregion 18c. A length and width of subregion 18c are determined from data required in returning the flight path from one of the potential flight path deviating conditions.
A long-term profile subregion 18d, beginning approximately 7 nautical miles along flight path 10 relative to aircraft 16 to approximately 20 nautical miles along flight path 10 relative to aircraft 16, is the most narrow portion of region 18. The width of subregion 18d may be a single data post 14 such that major terrain variation directly along path 10 may be considered well in advance.
FIG. 2 illustrates a terrain profile 40 generated from region 18. Profile section 40a corresponds to flight path 10 within subregioa 18a, section 40b within subregioa 186, section 40c within subrcgion 18c, and section 40d within subregioa 18d.
The method of transforming sample region 18 into terrain profile 40 may take a variety of Z D forms. Under any such method of conver'ang sample region 18 into terrain profile 40, however, it is assumed that the computational time and resources required are a function of the number of data posts considered. Thus, because the method of analysis under the present invention allows generation of as acceptable , i.e., safe or coaqervative, terrain profile based on a relatively smaller volume of DTED
data, the method of the present invention o$'ers an advantage in lesser computational time and resource requirem~ts while maintaining strict safety criteria.
Under the present invention, tile volume of DTED database 12 data gathered and analyzed is minimized according to its use. The subregion 18a accounts for that portion of database I2 necessary for executing most terrain following eomcr~aads.
3 0 Processing of database 12 is thereby minimized by e~ctracting data relevant to most terrain following flight commands. The subregion 18b is larger in volume, but must be considered in generating terrain profile 40 in the event of unexpected flight path 10 $_ deviation. A relatively smaller voluuze of database 12, i.e.. subregions 18c and 13d, is availahie to anticipate conditions more distant from aircraft 16.
as aircraft l 6 moves along flight path 10 the sample region 18 defines which portions of database 12 are reviewed or sauipled for analysis. The subregions 1Sa-18d thereby change dynamically with respect to database 12 as aircraft 16 moves forNard along flight path 10. Thus, at any given time aircraft 16 has available the sample region 18 for analysis is generating terrain profile 40 and executing flight terrain.
Following maneuvers.
A, Variety of methods of extracting DTE'D data conforming to sample region 18 may be ernpioyed undex the present invention. It is eontetnplated that the extraction of sample region 18 relative to flight path 10 and aircraft 16 be by software.
implementation. Qnce the overall dimension criteria far sample region ? 8 is ~tabLished, it is considered within tire ordinary skill of one in relevant art to extract the sample region 18 an;d ge~aerate a terrain profile 40 according to a sriven terrain profile transformation algorittun, i.e. convert sample region 18 into terrain profile 40.
By limiting the volume of information extracted from and analyzed under texrain following flight algorithms, the presemt invention makes terrain foiiewiag flight more efficient and accurate by considering only those terrain fearsrss relevant to the curxent flight path and potential deviations therefrom. extraneous portions of DT~D database 12 are not extracted and not analyzed. Ac:.ordiztgly, overall computational throughput and memory requirements for the terrain following f~.i~t algorithm are suostantiall,~ reduced in accordance with the present invention without compromising the integrity of the terrain following flight al?orithm.
'phe method of the present invention caz~templates generation of a terrain profile which may be used alone, or integrated with short range active sensor data.
When used in caz~junction with active sensor data, the active sensors need only be operated at low power settings. As a result, aircraft is visible to hostile forces only within several nautical miles of aircraft position. In this coordinated use, the terrain profile 40 simulates a long range sensor capability for anticipating terrain conditions 3 0 , and dictet'tng long range terrain following flight maneuvers.
..:.
a he active sensors contribute real terrain condition data serving as a short range sensor in the inzmesli.ate vicinity of the aircraft. Thus, as additional short range terrain profile representing the immediate proximity of the aircraft can be based on active sensor data.. The mere distant portions of the terrain as represented by terrain profile 44 are based on sample region 18.
The aircraft remains relatively hidden 'vy using low power active sensors, but possesses the tactical advantage of considering tez~rain candirions at a substantial distance from the aircraft position. i~iormally, to have the benefit of such long distance terrain profile information, the pilot would have to operate the active sensors at high power and undesirably make the aircrafrt visible to hostile forces from tong distances. Alternatively, a tc:rain profile could be generated from a D"1">rD
database, but such terrain profile generation has, heretofore, bern cocnnutationally burdensome and not well adapted for dynamic operation, i.e., during flight, due to the volume of data normally extracted :or such terrain profle generation. Generation of a terrain profile under the present ~aveation, however, is acxomplished at greater speed and, therefore, be more easily :ategx3ted into a dynamic in-flight terrain larofile generating algorithm.
The method of DTED database analysis of the present invention maximizes safety while allowing !owcr :errain following flight. In utili~,ng a.
prepianned flight route, the present invenucn capitalizes on a complete knowledge of the mission.
When analyzing a predic:ed rouu based on aircraft atti*a~de and velocity vectors, the present in~~ention need not be limited by use of active sensor data.
Accordingly, the rrsethod of the present invention is not liumited by a sensor field of view and can consider "hiddr,.n terrain", i. e.. :errain normally hidden from sensor view.
Because the method of the present inwsltion relies prir~tarily on the DTED database 12, all terrain :~s visible and availa't~le ;or analysis. 3n contrast, in terrain following systems relying an active sensor data ce.~tain terrain is masked by terrain profile, especially when f)ying at low above ground elevations, and therefore unavailable for aaticigating flight ~o.aneuvers. Thus, tine merhod of the present znventian allows lower average elevation 3 0 because the aircraft need not travel at relatively higher altitudes to generate a terrain profile by use of active sensor data. The "real" terrain conditions are represented by _, short range sensor equipment presenting limited risk of visibilir~ to hostile forc$s.
Long range terrain profile information is obtained efficiently, under the gresent invention, from the DTED daxa base 12 and is available for complete analysis of upcoming terrain in anticipating terrain following flight maneuvers.
The method of generating a terrain profile under the present invention may take into account a variety of factors including typical pilot response times and particular aircraft iunfotmativa such as response tinge aid flight maneuvezing capabilities. The specific mission may be characterized by taking all such parameters into account in selecting the width and length of the various subregions of sample region 18.
The specific dimensions, including length and width for the subregions 18a-18d are generahy mission aid aircraft specific. It is notconsidered possible to set Earth specific dimensions ar formula to calculate dimensions for these subregiorss. tLs noted above, each subregion is dimensioned according to expected use of the data. In L5 implementation of the present invention, actual flight data is considered the best method to generate dimensional values for the subregions 18a-I 8d. Such flight darn was obtained by logging aircraft position relative to an expected fligat Bath and anaiyaing this data to establish criteria for dimensioning the subregians 18a-i8d.
For example, by analyzing an actual flight path relative to an expected flight 2o path a statistical deviation from expected flight path may be derived. This statistical deviation could, for example, correlate generally to the subregiva 18c and to the subregioa 18b. The subregioa l8b could then be made larger or smaller relative to this statistical deviation as a funciion of the magnitude of safety one wishes to incorporate into the terrain profile generating aigorithfn. If a broad spectrum of 25 unexpected flight path deviating conditions are to be allowed, i.e., a conservative safety margin, the subregiotl 18b would be correspondingly larger. if, however, the algorithm is to accept a certain degree of risk by not allowing consideration of a broad range of unexpected flight deviating conditions, the subregion 18b could be riaade correspondingly smaller. The subregion 18d has bees found to be effective at the least 3 0 width magnitude, i.e., a width o~ one data post 14, as a good indicator of general terrain conditions well is advance of aircraft 16 position.
Thus, it is suggested that actual flight data be employed to generate the dimensional requirements for the subregions 18a-18d. 'fhe specific dimnensions For these sample subrcgions may be developed in conjunction with overall mission strategy and safety factors considered. For example, if the aircraft is to execute terrain ~oiiowing flight at extremely high speeds without use of long range active sensor data, the execution time requirements in generating the terrain profile may require that a very small volume of DT~D data be used in generating the terrain profile.
Conversely, if the aircraft is traveling at slower speeds or aircraft safety is a larger concern, a correspondingly larger dunensioned sample region 18 may be employed to meet these mission specific criteria.
Accordingly, no specific calculation or formula can be provided far general use, but is contemplated that the present invention allow for adjustment in the dimensioning of the sample region 18 to meet such spcci=ic criteria, i.e., the sample region 18 is dimensioned according to ita expected use and mission specif c parameters.
This invention has been described herein in considerable detail in order to comply with the Patent Statutes and to provide those skilled in the art with floe information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the 2o invention is n.ot restricted to the particular embodiment that has been described and illustrated, but can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope o~the invention itself.
What is claimed is:
and comQutatioas based on extracted DTED are not sirnpiy improvements in computational elegance, but can be life-saving and critical to mu.ssion success.
Terzain profiles have been built by extracting a massive volume of DTED data with reference to a designated flight Bath. As may be appreciated, each data sample Liken from the DTED database far consideration is generating the terrain profile requires a given amount of processing time. The data extracted from the DTED
database for generating the terrain profile corresponded to data posts lying along a length of the fliglat path preceding aircraft position and all data posts within a given distance of that length portion, i.e, a fixed length and ~~idth region of data posts along the flight path and identified relative to current aircraft position. The terrain profile :nest provide safe, conservative information. To this end, a large volume of DTED
data has been incarpozated into terrain profiles. Unfot'tunateiy, the volume of data extracted and processed has constrained terxain profile generation, i.e., has required excess terrain profile calculation time.
Thus, prior methods of generating terrain profiles include long range active s°nsozs, but long range sensor emissions make airczaft visible at long distances. These prior art methods have included DT):.D database systems, but generating conservative terrain profiles requires massive zzumbers of DTED data points and can require 2 0 relativ ely long calculation ti me.
A relevant prior art reference is European Patent application 0 499 874, a ray-tracing algorithm method with a digital database to process only the visible surfaces in a field of view. During operation to different sets of inforaiacion are analyzed. The first is a constant width data corridor comprising a narrow and of high resolution data.
Second is a widex band of lower resolution data_ The focus of this invention is the resolution of the data in the particular corridor. , It is desirable, therefore, that terrain following flight be executed without aid of high power, long range active sensor data to avoid exposing the airc.-a~ to threat installations. It is fufther desirable that a method of producing a terrain pmfile for 3 ~ executing terrain following flight support dynamic and efficient calculation time.
SUlIr~VIARY CfF THF INV'EN"TION
In accordance with the present invention, an aircraft flight path is selected and a limited volume of DTED data points ase extracted from a DTED database to safely minimize the above wound level elevation at any given point during the terrain following flight. I~iore particularly, the DTED data points extracted from the database are takes from sample regions havimg dimension according to conditions such as time sad distance relative to the aircraft.
In accordance with a preferred embodiment of the present invention, each sample region is centered upon the selected flight path and positioned relative to the aircraft, but varies in width relative to other sample regions. Cmaerally, the wider 1o sample regions are near the aircraft, and sample regions more distaatfrom the aircraft along the selected flight path become increasing more narrow. The widest sample region corresponds to a portion of the flight path, at a given position relative to the aircraft, associated with potential aircraft flight path deviation. . Thus, additional terrain data is considered in the event of such unexpected deviation from the terrain i5 following flight path. In this manner, a relatively greater volume of DTED
data is extracted as needed. More distant terrain along the flight path is suitably evaluated, but using a lesser volume of DTED data. As a result, computational throughput and memory requirements for terrain following flight algorithms are minimized while maximizing terrain fallowi.ag performance and safety criteria.
2 o The raethod of generating a terrain profile is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation of the invention, together with further advantages and objects thereof, may best be understood by reference to the following ddcription taken with the accompanying drawings wherein like reference characters 2 5 refer to like elements.
-4a-In accordance with one aspect of this invention, there is provided a method of generating a terrain profile on an aircraft's flight mission computer system using a sample region of digital terrain elevation data which corresponds to an aircraft's position and predicted flight path, the method comprising the steps: identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands, said plurality of sample regions include, said sample regions being updated as the aircraft progresses along the flight path; and transforming said plurality of sample regions into a terrain profile, wherein a first sample region is dimensioned according to short range terrain following flight command data needed, a second sample region is dimensioned according to potential flight path deviation data needed, and a third sample region is dimensioned according to long range terrain following flight data needed; the first sample region being an intermediate volume and closest to the aircraft, the second sample region being a greatest volume and next closest to the aircraft, and the third sample region being a least volume and most distant from the aircraft; and transforming data posts of said first, second, and third sample regions into a terrain profile.
In accordance with another aspect of this invention, there is provided a method of generating a terrain profile on an aircraft's flight mission computer system using a sample region of digital terrain elevation data which corresponds to the aircraft's position and predicted flight path, the method comprising the steps:
-4b-identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands; and transforming said plurality of sample regions into a terrain profile, wherein said plurality of sample regions include: a first sample region having length and width dimensions chosen as a function of data required for execution of terrain following flight commands for terrain in a vicinity of the aircraft; a second sample region located directly under and along said flight path and in advance of said first sample region relative to said aircraft position, said second sample region having length and width dimension which are directly related to potential flight path deviations caused by unexpected events; a third sample region with a length and width determined from data required in returning to said flight path from one of said potential flight path deviating conditions; and a fourth sample region located furthest from said aircraft in relation to said first, second, and third sample regions, said fourth sample region having a minimum width dimension relative to the width dimensions of said first, second and third sample regions.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
-5.
FIG. 1 illustrates in plan. view a sample region taken from a DTED database in accordance with the present invention foc generating a terrain profile to aid in terrain following flight.
FIG. 2 illustrates a terrain profile generated frorn the sample reF.~'on of FIG 1.
DET,r'IIi.ED l?ESCRIPTIOlV OF TTr~ PREFERRED EMBODIMENT
FIG. 1 illustrates a flight Bath 10 with reference to a portion of a digital terrain elevation data (I7'f'ED~ database i2 comprising a grid of data posts 14. Each data post I~ is indicated in FIG. 1 as an "X", but no scale in data post 14 spacing is indicated nor is every data post 14 shown, DTED database 12 may take a variety of formats, but as relevant to the present invention may be taken generally as an X"Y
addressable array of data posts 1~, e.g., addressed by latitude and longitude, and providing elevation at a given location. The flight path 12 may be a flight path selected as part of a mission plan, or may be a flight path predicted dynamically as a function of the current aircraft attitude and velocity vectors. In either case, it is necessary to extract from the DTED database 12 elevation data xelaiive to flight path 10 to generate a terrain proftte in aid of terrain following flight tbesealoag.
Terrain following flight is executed in accordance with the present invention 2p by reference to the DTED database 1~ with little or no additio~aal active sensor data.
Any active sensors used would be at low power and detectable only within several nautical miles of the air~aft. It is desirable to cxecate such terrain following flight with a minimum above ground level elevation to minimize the aircra~ visibility arid vulnerability to attack from threat installations. Using a terrain profile based on DTED information, the aircraft can achieve such minimum above ground Level elevation by anricigating upcoming terrain conditions and minimizing above ground level elevation with resQect tv such anticipated terrain conditions taking into account aircraft and pilot flight capabilities and reaction times.
As may be aQpreciated, a DTED database can be huge and cornputationaily burdensome to analyze in its entirety, especially while dynamically executing terrain following flight. In accordance with the present inv ention, izowever, only a limited 2~ao5~
portion of database 12 need be extracted, i.e., sample zegion 18, for use in generating a terrain profile for executing terrain following flight. This minimizes the computation and memory requirements of such terrain following fligb~t. The sample. region includes a set of subrerions 18a-18d each selected dynamically as a function of aircraft 16 position along fight path 10.
A short-term profile subregiorl 18a exists along flight path 10 beginning at and e:rtending approximately 2 nautical miles in front of aircraft 16. 'the width of short-term profile subregion 18a may vary while in flight as a function of aircraft NAV
CEP, cross track deviation, and aircraft 16 wingspan This restricts fine adjustments l o of the terrain profile obtained to the xegion of database 12 from which most terrain following steering commands are most likely generated, i.e., the horizon,to clear is typicahy within 2 nautical males of the aircraft 16.
A first m.id-terra. profile subregion 18b, beginning at approximately 2 nautical miles in front of aircraft i6 along flight path 10 and terminating at approximately 5 nautical miles from aircraft 16, is relatively wider than that of short-term subregion I Sa. The width of mid-term subregion 18b may be a coBStant width, bat defined as a function of potential forces or conditions acting to drive the aircraft 16 off the selected or predicted flight path 10, Thus, to the extent that aircraft i6 may deviate from path 10, region 18b should be suitably wide enough to anticipate flight within this range of 2 Q potential deviation. The type of forces considered in establishing a width for mid-term subregion 18b can be generally characterized as unpredicted conditions.
Fur example, a sudden, unexpected sidewind may drive the aircraft off the flight path I0, or an unforeseen event may distrac~ the pilot and the aircraft might deviate to some r extent relative to flight path 10. Thus, in establishing the width of niid-term subregion 18b, a variety of potential path deviating conditions may be considered. Also;
the width calculation should tale into account specific information such as pilot resQonse dme to ungredicted events and the specific aircraft used, i.e., aircraft response to pilot commands, For example, a fast aircraft having relatively slow ground track response may require a relatively wider subregion 18b due to the relatively greater distance the aircraft could potentially deviate from flight path 10 due to its speed and relatively _?_ slow ground track respansc. Ia contrast, a slow, large aircraft may have fast ground track response and permit a relatively more narrow subregion 18b.
A second mid-term subrcgion 18c, beginning at approximately 5 nautical miles along flight path from aircraft 16 and terminating at approximately T nautical miles along flight path 10 relative to aircraft l6, is relatively more narrow than that of subregion 18b. It is assumed that the pilot will steer back onto path 10 is response to any path deviating forces detected in region 20 and thereby have the advantage of early consideration of the subregion 18c. A length and width of subregion 18c are determined from data required in returning the flight path from one of the potential flight path deviating conditions.
A long-term profile subregion 18d, beginning approximately 7 nautical miles along flight path 10 relative to aircraft 16 to approximately 20 nautical miles along flight path 10 relative to aircraft 16, is the most narrow portion of region 18. The width of subregion 18d may be a single data post 14 such that major terrain variation directly along path 10 may be considered well in advance.
FIG. 2 illustrates a terrain profile 40 generated from region 18. Profile section 40a corresponds to flight path 10 within subregioa 18a, section 40b within subregioa 186, section 40c within subrcgion 18c, and section 40d within subregioa 18d.
The method of transforming sample region 18 into terrain profile 40 may take a variety of Z D forms. Under any such method of conver'ang sample region 18 into terrain profile 40, however, it is assumed that the computational time and resources required are a function of the number of data posts considered. Thus, because the method of analysis under the present invention allows generation of as acceptable , i.e., safe or coaqervative, terrain profile based on a relatively smaller volume of DTED
data, the method of the present invention o$'ers an advantage in lesser computational time and resource requirem~ts while maintaining strict safety criteria.
Under the present invention, tile volume of DTED database 12 data gathered and analyzed is minimized according to its use. The subregion 18a accounts for that portion of database I2 necessary for executing most terrain following eomcr~aads.
3 0 Processing of database 12 is thereby minimized by e~ctracting data relevant to most terrain following flight commands. The subregion 18b is larger in volume, but must be considered in generating terrain profile 40 in the event of unexpected flight path 10 $_ deviation. A relatively smaller voluuze of database 12, i.e.. subregions 18c and 13d, is availahie to anticipate conditions more distant from aircraft 16.
as aircraft l 6 moves along flight path 10 the sample region 18 defines which portions of database 12 are reviewed or sauipled for analysis. The subregions 1Sa-18d thereby change dynamically with respect to database 12 as aircraft 16 moves forNard along flight path 10. Thus, at any given time aircraft 16 has available the sample region 18 for analysis is generating terrain profile 40 and executing flight terrain.
Following maneuvers.
A, Variety of methods of extracting DTE'D data conforming to sample region 18 may be ernpioyed undex the present invention. It is eontetnplated that the extraction of sample region 18 relative to flight path 10 and aircraft 16 be by software.
implementation. Qnce the overall dimension criteria far sample region ? 8 is ~tabLished, it is considered within tire ordinary skill of one in relevant art to extract the sample region 18 an;d ge~aerate a terrain profile 40 according to a sriven terrain profile transformation algorittun, i.e. convert sample region 18 into terrain profile 40.
By limiting the volume of information extracted from and analyzed under texrain following flight algorithms, the presemt invention makes terrain foiiewiag flight more efficient and accurate by considering only those terrain fearsrss relevant to the curxent flight path and potential deviations therefrom. extraneous portions of DT~D database 12 are not extracted and not analyzed. Ac:.ordiztgly, overall computational throughput and memory requirements for the terrain following f~.i~t algorithm are suostantiall,~ reduced in accordance with the present invention without compromising the integrity of the terrain following flight al?orithm.
'phe method of the present invention caz~templates generation of a terrain profile which may be used alone, or integrated with short range active sensor data.
When used in caz~junction with active sensor data, the active sensors need only be operated at low power settings. As a result, aircraft is visible to hostile forces only within several nautical miles of aircraft position. In this coordinated use, the terrain profile 40 simulates a long range sensor capability for anticipating terrain conditions 3 0 , and dictet'tng long range terrain following flight maneuvers.
..:.
a he active sensors contribute real terrain condition data serving as a short range sensor in the inzmesli.ate vicinity of the aircraft. Thus, as additional short range terrain profile representing the immediate proximity of the aircraft can be based on active sensor data.. The mere distant portions of the terrain as represented by terrain profile 44 are based on sample region 18.
The aircraft remains relatively hidden 'vy using low power active sensors, but possesses the tactical advantage of considering tez~rain candirions at a substantial distance from the aircraft position. i~iormally, to have the benefit of such long distance terrain profile information, the pilot would have to operate the active sensors at high power and undesirably make the aircrafrt visible to hostile forces from tong distances. Alternatively, a tc:rain profile could be generated from a D"1">rD
database, but such terrain profile generation has, heretofore, bern cocnnutationally burdensome and not well adapted for dynamic operation, i.e., during flight, due to the volume of data normally extracted :or such terrain profle generation. Generation of a terrain profile under the present ~aveation, however, is acxomplished at greater speed and, therefore, be more easily :ategx3ted into a dynamic in-flight terrain larofile generating algorithm.
The method of DTED database analysis of the present invention maximizes safety while allowing !owcr :errain following flight. In utili~,ng a.
prepianned flight route, the present invenucn capitalizes on a complete knowledge of the mission.
When analyzing a predic:ed rouu based on aircraft atti*a~de and velocity vectors, the present in~~ention need not be limited by use of active sensor data.
Accordingly, the rrsethod of the present invention is not liumited by a sensor field of view and can consider "hiddr,.n terrain", i. e.. :errain normally hidden from sensor view.
Because the method of the present inwsltion relies prir~tarily on the DTED database 12, all terrain :~s visible and availa't~le ;or analysis. 3n contrast, in terrain following systems relying an active sensor data ce.~tain terrain is masked by terrain profile, especially when f)ying at low above ground elevations, and therefore unavailable for aaticigating flight ~o.aneuvers. Thus, tine merhod of the present znventian allows lower average elevation 3 0 because the aircraft need not travel at relatively higher altitudes to generate a terrain profile by use of active sensor data. The "real" terrain conditions are represented by _, short range sensor equipment presenting limited risk of visibilir~ to hostile forc$s.
Long range terrain profile information is obtained efficiently, under the gresent invention, from the DTED daxa base 12 and is available for complete analysis of upcoming terrain in anticipating terrain following flight maneuvers.
The method of generating a terrain profile under the present invention may take into account a variety of factors including typical pilot response times and particular aircraft iunfotmativa such as response tinge aid flight maneuvezing capabilities. The specific mission may be characterized by taking all such parameters into account in selecting the width and length of the various subregions of sample region 18.
The specific dimensions, including length and width for the subregions 18a-18d are generahy mission aid aircraft specific. It is notconsidered possible to set Earth specific dimensions ar formula to calculate dimensions for these subregiorss. tLs noted above, each subregion is dimensioned according to expected use of the data. In L5 implementation of the present invention, actual flight data is considered the best method to generate dimensional values for the subregions 18a-I 8d. Such flight darn was obtained by logging aircraft position relative to an expected fligat Bath and anaiyaing this data to establish criteria for dimensioning the subregians 18a-i8d.
For example, by analyzing an actual flight path relative to an expected flight 2o path a statistical deviation from expected flight path may be derived. This statistical deviation could, for example, correlate generally to the subregiva 18c and to the subregioa 18b. The subregioa l8b could then be made larger or smaller relative to this statistical deviation as a funciion of the magnitude of safety one wishes to incorporate into the terrain profile generating aigorithfn. If a broad spectrum of 25 unexpected flight path deviating conditions are to be allowed, i.e., a conservative safety margin, the subregiotl 18b would be correspondingly larger. if, however, the algorithm is to accept a certain degree of risk by not allowing consideration of a broad range of unexpected flight deviating conditions, the subregion 18b could be riaade correspondingly smaller. The subregion 18d has bees found to be effective at the least 3 0 width magnitude, i.e., a width o~ one data post 14, as a good indicator of general terrain conditions well is advance of aircraft 16 position.
Thus, it is suggested that actual flight data be employed to generate the dimensional requirements for the subregions 18a-18d. 'fhe specific dimnensions For these sample subrcgions may be developed in conjunction with overall mission strategy and safety factors considered. For example, if the aircraft is to execute terrain ~oiiowing flight at extremely high speeds without use of long range active sensor data, the execution time requirements in generating the terrain profile may require that a very small volume of DT~D data be used in generating the terrain profile.
Conversely, if the aircraft is traveling at slower speeds or aircraft safety is a larger concern, a correspondingly larger dunensioned sample region 18 may be employed to meet these mission specific criteria.
Accordingly, no specific calculation or formula can be provided far general use, but is contemplated that the present invention allow for adjustment in the dimensioning of the sample region 18 to meet such spcci=ic criteria, i.e., the sample region 18 is dimensioned according to ita expected use and mission specif c parameters.
This invention has been described herein in considerable detail in order to comply with the Patent Statutes and to provide those skilled in the art with floe information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the 2o invention is n.ot restricted to the particular embodiment that has been described and illustrated, but can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment details and operating procedures, can be accomplished without departing from the scope o~the invention itself.
What is claimed is:
Claims (3)
1. A method of generating a terrain profile on an aircraft's flight mission computer system using a sample region of digital terrain elevation data which corresponds to an aircraft's position and predicted flight path, the method comprising the steps:
identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands, said plurality of sample regions include, said sample regions being updated as the aircraft progresses along the flight path; and transforming said plurality of sample regions into a terrain profile, wherein a first sample region is dimensioned according to short range terrain following flight command data needed, a second sample region is dimensioned according to potential flight path deviation data needed, and a third sample region is dimensioned according to long range terrain following flight data needed;
the first sample region being an intermediate volume and closest to the aircraft, the second sample region being a greatest volume and next closest to the aircraft, and the third sample region being a least volume and most distant from the aircraft; and transforming data posts of said first, second, and third sample regions into a terrain profile.
identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands, said plurality of sample regions include, said sample regions being updated as the aircraft progresses along the flight path; and transforming said plurality of sample regions into a terrain profile, wherein a first sample region is dimensioned according to short range terrain following flight command data needed, a second sample region is dimensioned according to potential flight path deviation data needed, and a third sample region is dimensioned according to long range terrain following flight data needed;
the first sample region being an intermediate volume and closest to the aircraft, the second sample region being a greatest volume and next closest to the aircraft, and the third sample region being a least volume and most distant from the aircraft; and transforming data posts of said first, second, and third sample regions into a terrain profile.
2. The method according to claim 1 wherein each of said plurality of sample regions has a width that varies with respect to other sample regions, and wherein said width among said plurality of sample regions is selected as a function of the aircraft's position along said predicted flight path.
3. A method of generating a terrain profile on an aircraft's flight mission computer system using a sample region of digital terrain elevation data which corresponds to the aircraft's position and predicted flight path, the method comprising the steps:
identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands; and transforming said plurality of sample regions into a terrain profile, wherein said plurality of sample regions include:
a first sample region having length and width dimensions chosen as a function of data required for execution of terrain following flight commands for terrain in a vicinity of the aircraft;
a second sample region located directly under and along said flight path and in advance of said first sample region relative to said aircraft position, said second sample region having length and width dimension which are directly related to potential flight path deviations caused by unexpected events;
a third sample region with a length and width determined from data required in returning to said flight path from one of said potential flight path deviating conditions; and a fourth sample region located furthest from said aircraft in relation to said first, second, and third sample regions, said fourth sample region having a minimum width dimension relative to the width dimensions of said first, second and third sample regions.
identifying a plurality of sample regions located directly under and along the predicted flight path of the aircraft, said sample regions varying in dimension according to use criteria including possible short range terrain following commands, potential flight path deviations, and long range terrain following commands; and transforming said plurality of sample regions into a terrain profile, wherein said plurality of sample regions include:
a first sample region having length and width dimensions chosen as a function of data required for execution of terrain following flight commands for terrain in a vicinity of the aircraft;
a second sample region located directly under and along said flight path and in advance of said first sample region relative to said aircraft position, said second sample region having length and width dimension which are directly related to potential flight path deviations caused by unexpected events;
a third sample region with a length and width determined from data required in returning to said flight path from one of said potential flight path deviating conditions; and a fourth sample region located furthest from said aircraft in relation to said first, second, and third sample regions, said fourth sample region having a minimum width dimension relative to the width dimensions of said first, second and third sample regions.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/183,531 US6005581A (en) | 1994-01-18 | 1994-01-18 | Terrain elevation path manager |
| US08/183,531 | 1994-01-18 | ||
| PCT/US1995/000638 WO1995019609A1 (en) | 1994-01-18 | 1995-01-17 | Terrain elevation path manager |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2181457A1 CA2181457A1 (en) | 1995-07-20 |
| CA2181457C true CA2181457C (en) | 2006-04-04 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002181457A Expired - Fee Related CA2181457C (en) | 1994-01-18 | 1995-01-17 | Terrain elevation path manager |
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| Country | Link |
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| CA (1) | CA2181457C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111750824A (en) * | 2020-06-05 | 2020-10-09 | 广州极飞科技有限公司 | Method and device for determining terrain state, electronic equipment and storage medium |
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1995
- 1995-01-17 CA CA002181457A patent/CA2181457C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111750824A (en) * | 2020-06-05 | 2020-10-09 | 广州极飞科技有限公司 | Method and device for determining terrain state, electronic equipment and storage medium |
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| CA2181457A1 (en) | 1995-07-20 |
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