CN105823469A - GNSS high precision assisted unmanned plane aerotriangulation method - Google Patents

Abstract

The invention discloses a GNSS high precision assisted unmanned plane aerotriangulation method. An airborne GNSS receiver, a GNSS base station receiver, and a camera are used together to carry out simultaneous observation. The aerotriangulation method comprises the following steps: accurately recording the exposure time of a camera by an airborne GNSS receiver, utilizing carrier phase to carry out differential calculation so as to obtain the information (centimeter level) of the position of an antenna; performing an interpolation method to obtain the external orientation line element of the exposure time of the camera; taking the external orientation line element as the primary data, in combination with a few of ground control points, carrying out an automatic treatment by aerotriangulation software to obtain the exterior orientation elements of each image, and further producing the required 4D images. A differential positioning method is adopted, after eccentric distance correction, the GNSS differential position information is used to replace the position information of exposure points, thus the line elements, which are needed in aerial photogrammetry, of external orientation element, can be obtained; the efficiency of unmanned plane low altitude photogrammetry is greatly improved, and the field surveying amount is reduced.

Description

A kind of GNSS high accuracy empty three measuring methods of auxiliary unmanned plane

Technical field

The present invention relates to the photogrammetric field in low latitude, specifically a kind of GNSS high accuracy empty three measuring methods of auxiliary unmanned plane.

Background technology

Traditional aerophotogrammetry is used to solve the one-tenth figure of the small scale in big region more; figure problem is become for the zonule large scale occurred in fields of measurement in recent years; if still using conventional aeroplane photography often to there will be, cost is high, maneuverability is poor, affected the problems such as big by weather, so low latitude based on low-altitude unmanned vehicle and conventional digital camera triangulation technique is the hot issue in the most photogrammetric field.Generally its data acquisition unit used is usually low latitude photographic platform (unmanned plane, unmanned airship etc.) and the integrated small-sized digital camera (Canon 5D_Mark II) of common many camera lenses, the former is because of features such as its quality are little, flight flying height is low, thus its easily affected by air-flow, course line keeps difficulty and flexibility is big, photo rotation drift angle is little compared with degree of overlapping regularity big, image relative to conventional aerophotogrammetry；The latter's its breadth when obtaining image is less, corresponding ground coverage is limited, this results in the number of its photo under identical survey area can be more than photo number during conventional aerial triangulation, the number of photo junction point during encryption also can be more than conventional aerial triangulation, if now still lay ground photo control point according to the requirement of traditional aerial angular measurement, field operation, the workload of interior industry will be increased greatly.

Since eighties of last century the mid-80, rise and GPS location technology is applied in field of aerial photography measurement reach to reduce the research of even completely eliminated ground control point, thus shortened duty cycle to a great extent, reduce working strength, improve work efficiency, reduce production cost etc..This technology is widely used in traditional aerophotogrammetry, such as western mapping and traditional 4D production etc..But in low altitude photogrammetry, still continue to use is traditional aerophotogrammetric encryption points distributing method, can lay according to GB " GBT13977-19921:5000,1:10000 topography aerophotogrammetry field operation specification ".When unmanned plane is taken photo by plane, after its image, quantity, often more than 48 width figures (containing 48 width), uses periphery multipoint method to lay flat high point.On course, the span of adjacent control points is estimated according to airline network accuracy estimation formulas:

$M_s=\±0.28\·m_q\sqrt{n^3+2n+46}$

In formula, M_S, error (mm) in the plane of pass point；m_q, error (mm) in the weight unit that parallax measures；Other to control point on level land, hilly ground less than 3 course lines, mountain region, high mountain region are less than 4 course lines.

At present, the method and system (can be found in Chinese patent CN201410483196) of a kind of GNSS/IMU integration unmanned plane mapping that Huang Jianhui of Jia Hong Science and Technology Ltd. of BeiJing ZhongKe et al. proposes, the program is integrated with GPS and Inertial Measurement Unit, it is provided that a kind of unmanned plane carries out aerophotogrammetric method and system.But the program has the disadvantage that 1) the clearest for the composition description of whole system；2) effect that GNSS and IMU both sensors are undertaken in this scenario is unclear.

Summary of the invention

It is an object of the invention to provide a kind of GNSS high accuracy empty three measuring methods of auxiliary unmanned plane, the method using Differential positioning, the positional information of exposure point is replaced with the differentiated positional information of GNSS, thus obtain the line element in elements of exterior orientation required in aerophotogrammetry, it is greatly enhanced the efficiency of unmanned plane low altitude photogrammetry, reduces field process amount.

For achieving the above object, the present invention provides following technical scheme:

A kind of GNSS high accuracy empty three measuring methods of auxiliary unmanned plane, utilize airborne GNSS receiver, GNSS base station receiver, camera simultaneous observation, described method includes: the camera exposure time under airborne GNSS receiver accurate recording, carrier phase Difference Solution is utilized after calculating, to obtain the Centimeter Level positional information of antenna, interpolation obtains the exterior orientation line element in camera exposure moment again, as known date, empty three softwares are used to carry out full automatic treatment in conjunction with a small amount of ground control point, obtain the elements of exterior orientation of each photo, and then produce required 4D image, it is greatly enhanced the efficiency of unmanned plane low altitude photogrammetry, reduce field process amount.

As the further scheme of the present invention: be reserved with signal input interface in usual airborne GNSS receiver, in unmanned plane is taken photo by plane, signal source mainly has two types: one is pulse active signal, and another kind is relay switch passive signal；In order to ensure that airborne GNSS receiver energy synchronism stability records signal time, one is to increase light even isolation circuit on signal input circuit, prevents signal mutual interference in equipment room signals transmission；Two is that input signal is drawn high airborne GNSS receiver signal operating high voltage, prevents signal attenuation in equipment room signals transmission；Three is to concatenate anti-ESD chip on signal input circuit, and anti-stop signal is by static interference；Four is concatenation magnetic bead on signal input circuit, and anti-stop signal is by RF noise jamming；Above 4 measure basic goals are to increase the stability of signal, to guarantee that airborne GNSS receiver is precisely recorded camera and taken pictures the T/A of moment.

As the further scheme of the present invention:

Described GNSS high accuracy empty three processing methods of auxiliary unmanned plane, comprise the following steps:

1) according to conditions such as the area in region to be surveyed and drawn, shape, positions, in ground control system (abbreviation flight control system) software of unmanned plane, draw the parameter such as flight path figure, exposure point position, in surveying district, select suitable GNSS base station location；

2) high-precision GNSS differential receivers antenna is arranged on as far as possible the surface of camera, to reduce the distance between GNSS resolving position and the position of actually required principal point；GNSS receiver part then selects suitable position to fix inside unmanned cabin, carries out glissando simultaneously；Connect signal socket, flight control system and the camera interface reserved in airborne GNSS receiver；

3) after before unmanned plane takes off, every inspection work completes, start shooting in GNSS base station, and airborne GNSS receiver is started shooting, and waits and searches after star completes, records data, allows unmanned plane take off；

4) unmanned plane is according to airline operation planned in advance, and camera is assigned appointment of taking pictures in the place specified, and the most airborne GNSS receiver also can record temporal information corresponding when taking pictures, and the number of the two is consistent, and time error is within 10us；

5) take photo by plane after end, collect the data of GNSS base station receiver, the data of airborne GNSS receiver, utilize the double difference carrier phase observation data of the two, carry out GNSS difference post processing and resolve, obtain the positional information of Centimeter Level；

6) utilize the relation between the camera exposure time of record and GNSS sampling epoch time to carry out interpolation, obtain the antenna coordinate in camera exposure moment；Recycle existing coordinate transformation parameter, by the coordinate reduction of above-mentioned coordinate and ground photo control point under same absolute reference coordinate system；Because relative position when antenna is installed in unmanned plane with camera is fixing, therefore after eccentricity correction, just need to can obtain the coordinate of camera；

7) antenna coordinate under above-mentioned same reference frame and a small amount of ground control point (4, periphery or 6 points) are carried out bundle adjustment, image measurer is utilized to carry out the automatic turning point of photo junction point, ground control point according to the artificial interpretation on image of aerophotogrammetry code requirement, its image plane coordinate of stereopsis.

Aerial triangulation is a link important in aerophotogrammetry, and the basic object of aerial triangulation is to ask for camera to expose position and the attitude information of moment, 6 elements of exterior orientation namely often said:X in formula_S, Y_S, Z_SIt is the phase center of the camera coordinate under rectangular coordinate system in space, i.e. three axis elements,ω, κ are the angle of pitch of photo, roll angle, course angle, i.e. angle element.Aerial triangulation based on bundle adjustment, adjusts the elements of exterior orientation of boat sheet by iterative method, it is achieved the same place of the boat sheet of overlapping region spatially intersects at light beam, and to obtain the elements of exterior orientation of boat sheet, reduction boat sheet is in the shape of exposure moment.Projection centre at the object point coordinate of object space, camera lens and this object point imaging point three point on a straight line on boat sheet meets Fundamentals of Mathematics conllinear formula:

$x=x_0-f\frac{a_1(X-X_S)+b_1(Y-Y_S)+c_1(Z-Z_S)}{a_3(X-Z_S)+b_3(Y-Y_S)+c_3(Z-Z_S)}---\left(1\right)$

$y=y_0-f\frac{a_2(X-X_S)+b_2(Y-Y_S)+c_2(Z-Z_S)}{a_3(X-Z_S)+b_3(Y-Y_S)+c_3(Z-Z_S)}---\left(2\right)$

In formula: { x₀, y₀, f} is the elements of interior orientation of boat sheet, the i.e. principal point coordinate in image plane coordinate and aerial surveying camera lens focus；{ x, y} are picture point coordinates in photo coordinate system；{ X, Y, Z} are ground some coordinates in object coordinates system；{X_s, Y_s, Z_sIt it is projection centre coordinate in object coordinates system；Being the spin matrix being transformed into ground object coordinates system by image space coordinate system, the most each element is boat sheet attitude angleFunction.Needed for the parameter that determines be 6 elements of exterior orientation of every boat sheetWith each object point coordinate { X, Y, Z}.The exact position that can obtain antenna is resolved by the difference of carrier phase, the eccentric throw that the phase center of antenna phase center and camera is constituted can use the measurement of other means to obtain, and then reach to obtain the purpose of the location fix element of each boat sheet, but can there is system deviation in the measurement of constant value eccentric throw, therefore still need to some ground control points and carry out calibration compensation.

As the further scheme of the present invention: the pulse time that described airborne GNSS receiver synchronous recording flight control system sends to camera, and the precision of time synchronized both the moment of airborne GNSS receiver record and camera exposure moment is at 10 μ s.

As the further scheme of the present invention: obtain coordinate after described airborne GNSS receiver and GNSS base station receiver difference, need to be transformed into consistent with mapping coordinate system, then after eccentricity correction, empty three softwares could be imported and process.

Compared with prior art, the invention has the beneficial effects as follows:

In order to farthest reduce ground control point, the present invention uses the method for the mode of operation Differential positioning that current GNSS positioning precision is the highest, replace the positional information of exposure point with the differentiated positional information of GNSS, thus obtain the line element in elements of exterior orientation required in aerophotogrammetry.The present invention is greatly enhanced the efficiency of unmanned plane low altitude photogrammetry, reduces field process amount.

Accompanying drawing explanation

Fig. 1 is that GNSS assists low altitude photogrammetry flow chart；

Fig. 2 is that tradition aerophotogrammetry sky Acanthopanan trifoliatus (L.) Merr. is densely covered to set up an office；

Fig. 3 is Ping Gao control point+2, corner row's vertical control point；

Fig. 4 is vertical frames course line ,+2, Ping Gao control point, corner；

Fig. 5 is test block, Zibo partial image figure；

Fig. 6 is that GNSS difference resolves the aft antenna location drawing.

Detailed description of the invention

Below in conjunction with the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, it is clear that described embodiment is only a part of embodiment of the present invention rather than whole embodiments.Based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art are obtained under not making creative work premise, broadly fall into the scope of protection of the invention.

Embodiment 1

In the embodiment of the present invention, utilize GNSS to obtain final steps that high-precision positional information is the photogrammetric middle minimizing ground control point of unmanned plane.

Refer to Fig. 1～6, a kind of GNSS high accuracy empty three measuring methods of auxiliary unmanned plane, specifically comprise the following steps that

1) according to conditions such as the area in region to be surveyed and drawn, shape, positions, the parameter such as flight path figure, exposure point position is drawn in the ground control system software of unmanned plane, in order to improve the minimizing ratio of ground control point, two framework courses are laid at two ends in air strips as far as possible, its flying height is typically high than the height in course line by 15%, selects suitable GNSS base station location in surveying district；

2) high-precision GNSS differential receivers antenna is arranged on as far as possible the surface of camera, resolve the distance between position and the position of actually required principal point reducing GNSS, use ruler etc. measure three eccentric shafts of antenna and camera phase center away from；GNSS receiver part then selects suitable position to fix inside unmanned cabin, carries out glissando simultaneously；Connect signal socket, flight control system and the camera interface reserved in airborne GNSS receiver；

3) after before unmanned plane takes off, every inspection work completes, start shooting in GNSS base station, and airborne GNSS receiver is started shooting, and waits and searches after star completes, records data, allows unmanned plane take off；

4) unmanned plane is according to airline operation planned in advance, and camera is assigned appointment of taking pictures in the place specified, and the most airborne GNSS receiver also can record temporal information corresponding when taking pictures, and number photo clapped with the camera number of record is identical；

5) taking photo by plane after end, the collection data of base station receiver, the data of airborne GNSS receiver carry out GNSS difference post processing and resolve, and wherein GNSS difference resolving principle is as follows: double frequency pseudorange observation formula is:

P₁=ρ+I (3)

$P_2=\mathrm{\ρ}+\frac{{\mathrm{\λ}}_2^2}{{\mathrm{\λ}}_1^2}*I---\left(4\right)$

Wherein, P₁And P₂Representing the Pseudo-range Observations of 2 channel B1 and B2 of the Big Dipper, ρ is receiver to the on-dispersive error such as the space length of satellite and troposphere, and I is the ionospheric error on B1, λ₁And λ₂Refer to the carrier wavelength of B1 and B2 respectively；

In like manner, dual-frequency carrier observation formula is:

(L₁+N₁)*λ₁=ρ-I (5)

$(L_2+N_2)*{\mathrm{\λ}}_2=\mathrm{\ρ}-\frac{{\mathrm{\λ}}_2^2}{{\mathrm{\λ}}_1^2}*I---\left(6\right)$

Wherein, L₁For the carrier phase observation data on B1；N₁For the fuzziness on B1；L₂For the carrier phase observation data on B2；N₂For the fuzziness on B2；

Formula (5) and formula (6) are merged, i.e. obtain wide lane side:

$(L1-L2+N1-N2)\frac{{\mathrm{\λ}}_1{\mathrm{\λ}}_2}{{\mathrm{\λ}}_1-{\mathrm{\λ}}_2}=\mathrm{\ρ}+\frac{{\mathrm{\λ}}_2}{{\mathrm{\λ}}_1}I---\left(7\right)$

Can be to be designated as following form:

$(L_W+N_W){\mathrm{\λ}}_W=\mathrm{\ρ}+\frac{{\mathrm{\λ}}_2}{{\mathrm{\λ}}_1}I---\left(8\right)$

Wherein, L_w=L₁-L₂；N_w=N₁-N₂It is referred to as wide lane ambiguity；λ_WFor wide lane wavelength；

Combination (3) and (4), express ρ and I for use pseudorange and ionosphere:

$\mathrm{\ρ}=\frac{{{\mathrm{\λ}}_1}^2{P}_2-{{\mathrm{\λ}}_2}^2{P}_1}{{{\mathrm{\λ}}_1}^2-{{\mathrm{\λ}}_2}^2}---\left(9\right)$

$I=\frac{{{\mathrm{\λ}}_1}^2{P}_1-{{\mathrm{\λ}}_1}^2{P}_2}{{{\mathrm{\λ}}_1}^2-{{\mathrm{\λ}}_2}^2}---\left(10\right)$

(9) and (10) are updated to formula (7), obtain:

$(L_W+N_W){\mathrm{\λ}}_W=\frac{{\mathrm{\λ}}_2{P}_1+{\mathrm{\λ}}_1{P}_2}{{\mathrm{\λ}}_1+{\mathrm{\λ}}_2}---\left(11\right)$

In formula (11), ionosphere and orbit error (including troposphere) are completely eliminated, N_WOnly by P₁, P₂, L₁, L₂The impact of noise, this has great advantage when resolving wide lane ambiguity, smooths the N of error within just obtaining a week the most tens of epoch_W；

Round and i.e. can get the N that accuracy is high_W, recycle N_WCarry out fuzziness N₁Search procedure；

When fuzziness N₁After Gu Ding, by detection and the reparation of cycle slip, i.e. may utilize equation below (12) carry out before and after the final position of all epoch resolve:

$\left[\begin{array}{c}(L_{1g}+N_{1g})*{\mathrm{\λ}}_{1g}\\ (L_{1g}+N_{1c})*{\mathrm{\λ}}_{1c}\end{array}\right]=\left[\begin{array}{c}{B}_g\\ B_c\end{array}\right]d_x---\left(12\right)$

If fuzziness N₁Do not fix, then utilize wide lane ambiguity N_WFinally position, but ratio of precision N₁Positioning slightly lower, formula is as follows:

$\left[\begin{array}{c}({\mathrm{Lw}}_g+{\mathrm{Nw}}_g)*{\mathrm{\λw}}_g\\ ({\mathrm{Lw}}_c+{\mathrm{Nw}}_c)*{\mathrm{\λw}}_c\end{array}\right]=\left[\begin{array}{c}{B}_g\\ B_c\end{array}\right]d_x---\left(13\right)$

6) formula (3) to (13) set forth in detail the ultimate principle using GNSS differential data to carry out hi-Fix, can obtain the position of each epoch in airborne GNSS receiver observation data；In view of the epoch of observation of above airborne GNSS receiver is timing acquiring, therefore interpolation need to be carried out by the camera exposure time data of record in airborne GNSS receiver and obtain the object coordinates of camera exposure moment, recycle existing coordinate transformation parameter so that the coordinate of antenna and the coordinate rule of ground photo control point are calculated under same absolute reference coordinate system；

null7) the antenna coordinate under above-mentioned same reference frame、Receiver antenna and the eccentric throw of camera phase center and a small amount of ground control point (4, periphery or 6 points)，SIFT feature coupling is used to mate, with pyramid image, the turning point strategy combined，Automatically extract the image connecting points between mapping course line，Use POS assisted image matching strategy，Complete the automatic turning point between control strip and mapping course line，The observation data difference using airborne receiver and ground static state receiver record obtains Centimeter Level positional information，The systematic error of station coordinates is taken the photograph for the image connecting points obtained and GNSS，Corresponding systematic error compensation model is used to utilize image measurer to carry out the automatic turning point of photo junction point in GNSS auxiliary beam method block adjustment，Ground control point is according to the artificial interpretation on image of aerophotogrammetry code requirement，Its image plane coordinate of stereopsis.

Utilizing the inventive method, carry out the low altitude photogrammetry experiment of unmanned plane in In Zibo, Shandong, wherein pilot region contains the multiple landform such as city, rural area, farmland, and area is about 40km², 1054 boat sheet compositions amount to 11 course lines, have laid 340 ground control points according to empty three encryption methods of tradition.Because being limited by flying condition, experiment does not flies control strip at two ends.The data processing method that the low altitude photogrammetry experiment of this unmanned plane relates to is as shown in table 1.

Table 1 data processing method is classified

Experimental analysis:

1, under the same terms of control point

Height accuracy: GPS auxiliary sky three is higher than the simple adjustment of control network；

Plane precision: GPS auxiliary sky three is higher than the simple adjustment of control network or close.

When 2, obtaining same precision on checkpoint

GPS auxiliary sky three is fewer than control point needed for the simple adjustment of control network.

Conclusion: be used for regional network simultaneous adjustment using taking the photograph station location determined by GPS as assistance data, the ground control point needed for conventional air triangulation can be reduced, a large amount of saving photo field measurement workloads.For mapping, this finally becomes control point in 1:1000 figure to arrange 340 altogether, uses wherein 40 additional GPS of point to assist empty 3 points, i.e. can reach equal accuracy, reduce by the control point of 80%.But owing to unmanned plane image sidelapping is uneven, unmanned plane GPS assists empty three effects photogrammetric not as conventional big aircraft.

In order to farthest reduce ground control point, the present invention uses the method for the mode of operation Differential positioning that current GNSS positioning precision is the highest, replace the positional information of exposure point with the differentiated positional information of GNSS, thus obtain the line element in elements of exterior orientation required in aerophotogrammetry.The present invention is greatly enhanced the efficiency of unmanned plane low altitude photogrammetry, reduces field process amount.

It is obvious to a person skilled in the art that the invention is not restricted to the details of above-mentioned one exemplary embodiment, and without departing from the spirit or essential characteristics of the present invention, it is possible to realize the present invention in other specific forms.Therefore, no matter from the point of view of which point, embodiment all should be regarded as exemplary, and be nonrestrictive, the scope of the present invention is limited by claims rather than described above, it is intended that all changes fallen in the implication of equivalency and scope of claim included in the present invention.

In addition, it is to be understood that, although this specification is been described by according to embodiment, but the most each embodiment only comprises an independent technical scheme, this narrating mode of description is only for clarity sake, description should can also be formed, through appropriately combined, other embodiments that it will be appreciated by those skilled in the art that as an entirety, the technical scheme in each embodiment by those skilled in the art.

Claims (8)

1. GNSS high accuracy empty three measuring methods of auxiliary unmanned plane, utilize airborne GNSS receiver, GNSS base station receiver, camera simultaneous observation, it is characterized in that, described method includes: the camera exposure time under airborne GNSS receiver accurate recording, carrier phase Difference Solution is utilized after calculating, to obtain the Centimeter Level positional information of antenna, interpolation obtains the exterior orientation line element in camera exposure moment again, as known date, empty three softwares are used to carry out full automatic treatment in conjunction with a small amount of ground control point, obtain the elements of exterior orientation of each photo, and then produce required 4D image.

GNSS the most according to claim 1 high accuracy empty three measuring methods of auxiliary unmanned plane, it is characterised in that have additional light even isolation circuit on the signal input circuit of described airborne GNSS receiver.

GNSS the most according to claim 1 high accuracy empty three measuring methods of auxiliary unmanned plane, it is characterised in that the input signal of described airborne GNSS receiver draws high GNSS receiver signal operating high voltage.

GNSS the most according to claim 1 high accuracy empty three measuring methods of auxiliary unmanned plane, it is characterised in that concatenate anti-ESD chip on the signal input circuit of described airborne GNSS receiver.

GNSS the most according to claim 1 high accuracy empty three measuring methods of auxiliary unmanned plane, it is characterised in that concatenate magnetic bead on the signal input circuit of described airborne GNSS receiver.

6. according to arbitrary described GNSS high accuracy empty three measuring methods of auxiliary unmanned plane of claim 1-5, it is characterised in that the pulse number of described airborne GNSS receiver record number of taking pictures with camera is consistent.

GNSS the most according to claim 6 high accuracy empty three measuring methods of auxiliary unmanned plane, it is characterized in that, the pulse time that described airborne GNSS receiver synchronous recording flight control system sends to camera, and the precision of time synchronized both the moment of airborne GNSS receiver record and camera exposure moment is at 10 μ s.

GNSS the most according to claim 1 high accuracy empty three measuring methods of auxiliary unmanned plane, it is characterized in that, coordinate is obtained after described airborne GNSS receiver and GNSS base station receiver difference, need to be transformed into consistent with mapping coordinate system after, correct through eccentric throw again, import empty three softwares and process.