CN108050995B - Oblique photography non-image control point aerial photography measurement area merging method based on DEM - Google Patents
Oblique photography non-image control point aerial photography measurement area merging method based on DEM Download PDFInfo
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- CN108050995B CN108050995B CN201711342200.5A CN201711342200A CN108050995B CN 108050995 B CN108050995 B CN 108050995B CN 201711342200 A CN201711342200 A CN 201711342200A CN 108050995 B CN108050995 B CN 108050995B
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Abstract
The invention discloses a method for merging oblique photography non-image control point measurement areas based on a DEM. The method comprises the following steps: step 1, calculating the DEM area range of each aerial photography area based on POS data of the unmanned aerial vehicle; step 2, constructing a regular grid digital elevation model of each measuring area by adopting a point-by-point interpolation method based on the DEM area range of the aerial photography measuring area; step 3, calculating the height of a DEM reference surface of the measuring area according to a flight line design standard in the low-altitude digital aerial photography standard, and determining a critical value of the altitude difference between every two adjacent measuring areas; step 4, calculating the actual altitude difference between every two adjacent measuring areas based on POS data of the unmanned aerial vehicle; and step 5, merging the measurement areas according to the fact that the actual altitude difference is smaller than the altitude difference critical value, and finally obtaining an aerial photography measurement area merging set which can carry out aerial triangulation calculation together. Compared with the traditional manual merging method, the method provided by the invention has the advantages that the matching accuracy and the dividing efficiency of the aerial photography area are greatly improved.
Description
Technical Field
The invention relates to a Digital Elevation Model (DEM) -based merging method for an oblique photography image-control-point-free aerial photography measurement area.
Background
With the development of parallel computing technology and the emergence of air triangulation technology based on Differential GPS Positioning (DGPS), rapid dense matching of massive, disordered and multi-resolution images becomes possible. The prior content Capture (original Smart3D) automatic three-dimensional reconstruction software in the industry can realize the rapid automatic production of large-scale real three-dimensional models without POS data and control points (GCP). However, in the aerial photogrammetry process of the unmanned aerial vehicle in the large-area mountainous area, the shooting area needs to be divided into a plurality of aerial photography areas when the unmanned aerial vehicle is in aerial photography due to the endurance time, the topographic relief and other reasons of the unmanned aerial vehicle. In order to avoid the problems of increasing the splicing times of live-action three-dimensional models, reducing the model precision due to splicing and the like, a plurality of aerial photography areas need to be combined as much as possible for aerial triangulation.
In recent years, many achievements have been made in the research of aerial triangulation accuracy of a single aerial photography area at home and abroad, including the influence of the arrangement method of the image control points on the aerial triangulation accuracy of the single aerial photography area, and the influence of the arrangement of the field control points on the aerial triangulation accuracy is greatly reduced; the adjustment of the beam method area network under different parameters influences the precision of aerial triangulation, and the algorithm in the aerial triangulation process is optimized. However, at present, the merging of the aerial photography areas without the image control points mainly uses the traditional manual merging method, which is relatively backward, and the merging mainly comprises the following points:
(1) merging of aerial photography measurement areas has no judgment index
The traditional manual merging method is to try to merge a plurality of aerial survey areas through personal experience to carry out aerial triangulation, judge the precision condition of the result, if so, continue to add the aerial survey areas until the aerial triangulation result added with the aerial survey areas cannot be oriented accurately. The traditional manual method completely relies on the experience of data processing personnel for merging, and the matching accuracy and the dividing efficiency are extremely low.
(2) Cannot be applied to aerial photography data processing in large-area mountainous areas
The traditional manual merging method depends on factors such as the number, the precision, the arrangement mode and the like of control points in the aerial photography data processing process of large-area mountainous areas. However, the difference in altitude between the aerial photography areas is often large due to the topographic relief in the mountainous area, and meanwhile, the collection at the control point in the mountainous area is more difficult in towns, so that the traditional manual merging method cannot be applied to large-scale mountainous area aerial photography data processing.
The defects of the traditional manual merging method used in the aerial photography area without the image control points cause great difficulties in accurate matching and rapid division of large-scale mountain aerial photography data and production of a live-action three-dimensional model. More importantly, as the accuracy of aerial triangulation by combining a plurality of aerial survey areas is limited by various factors such as the accuracy of original data, an adjustment method, an image control point arrangement method, the geometric strength of a regional network and the like, the efficiency of combining the aerial survey areas by using a traditional manual method is very low, and the waste of manpower and hardware resources is caused.
Disclosure of Invention
The invention aims to determine main factors and indexes influencing aerial triangulation precision of aerial photography area combination, and provides an automatic merging method by taking the factors as the basis of merging of aerial photography areas, so that the aerial photography areas without image control points are accurately and quickly merged to replace the traditional manual matching division method.
The technical scheme adopted by the invention is as follows:
a method for merging oblique photography non-image control point measurement areas based on DEM comprises the following specific steps:
step 1, calculating the regional range of a DEM (digital elevation model) of a measurement area by POS (point of sale) data:
obtaining POS data of unmanned aerial vehicles in each measuring area; screening out longitude and latitude coordinates of four corners of a measuring area in the POS data, and determining the longitude and latitude coordinates of the four corners of a DEM area range of the measuring area in a vertical projection mode;
step 2, establishing a regular grid digital elevation model of each measurement area:
after the regional scope of each measurement area DEM is determined, a regular grid digital elevation model of each measurement area is constructed by adopting a point-by-point interpolation method;
step 3, calculating a critical value of altitude difference:
firstly, calculating the height of a datum plane of a regular grid digital elevation model of each measuring area, wherein the formula is as follows:
wherein h isBase ofThe elevation of a datum plane of the measuring area digital elevation model is obtained; h isiThe elevation values of the grid points of the digital elevation model in the measuring area are obtained; n is the number of grid points of the digital elevation model in the measurement area;
then, determining a critical value of the altitude difference between every two adjacent measuring areas by using the altitude difference of the datum plane, wherein the formula is as follows:
wherein △ h is the critical value of altitude difference between adjacent measurement areas A and B, hRadical A、hRadical BThe height of a reference surface of a digital elevation model of a measuring area A and a measuring area B, nA、nBRespectively counting the grid points of the digital elevation models in the measurement area A and the measurement area B;
step 4, calculating the difference of the relative altitude average values between every two adjacent measuring areas based on POS data of the unmanned aerial vehicle, and taking the difference as the actual altitude difference between every two adjacent measuring areas;
and 5, generating a measuring area merging set: taking a certain measuring area as an initial measuring area, and determining measuring areas adjacent to the periphery of the initial measuring area; if the actual altitude difference between the initial measurement area and the adjacent measurement area is smaller than the altitude difference critical value, the adjacent measurement area can be merged with the initial measurement area, otherwise, the adjacent measurement area is not merged with the initial measurement area, and the adjacent measurement area is used as the initial measurement area again for cyclic judgment until each measurement area and the merged measurement area are used as the initial measurement area; finally, a merging set after merging the measuring areas is obtained, and the measuring areas in the merging set can be subjected to aerial triangulation calculation together.
In view of the fact that the main factor influencing aerial triangulation accuracy by combining aerial surveying areas under the condition of no image control point is the altitude difference between the aerial surveying areas, the method and the device realize the merging of the aerial surveying areas without the image control point on the basis of the altitude difference of the flight path datum planes between the aerial surveying areas DEM. Compared with the traditional manual merging method, the method disclosed by the invention has the advantages that the matching accuracy and the dividing efficiency of the aerial photography area are greatly improved, so that the method has stronger reference significance and higher application value for processing aerial photography data in large-area mountainous areas.
Drawings
FIG. 1 is a regional scope diagram of an aerial survey area DEM calculated by POS data according to the invention;
FIG. 2 is a diagram of a regular grid digital elevation model;
FIG. 3 is a schematic diagram of determining a critical value of the altitude difference of the reference plane of the adjacent aerial photography area;
FIG. 4 is a flow chart of a merging method;
FIG. 5 is a diagram of POS data distribution (light black points are orthographic aerial survey areas, dark black points are oblique aerial survey areas) of all aerial survey areas in an embodiment of the invention;
FIG. 6 is an enlarged view of a portion of the aerial survey area POS data of FIG. 5;
FIG. 7 is a DEM area range diagram of each aerial photography area in the embodiment of the invention;
fig. 8 is a diagram of the merging result of the aerial photography areas in the embodiment of the present invention.
Detailed Description
The technical idea of the invention is as follows: the method comprises the steps of firstly analyzing the altitude difference between the aerial photography areas as the main factor influencing the aerial photography area merging airspace three-precision under the condition of no image control point, and then automatically merging the aerial photography areas without the image control points on the basis of the DEM-based air route design specification in the low-altitude digital aerial photography specification. The method mainly comprises the following steps: firstly, calculating DEM area ranges of all aerial photography areas based on POS data of the unmanned aerial vehicle; secondly, constructing a regular grid digital elevation model of each measuring area by adopting a point-by-point interpolation method based on the DEM area range of the aerial photography measuring area; thirdly, calculating the height of a DEM reference surface of the aerial photography area according to a flight line design standard in the low altitude digital aerial photography standard and determining a critical value of the altitude difference between every two adjacent aerial photography areas; fourthly, calculating the actual altitude difference between every two adjacent aerial photography areas based on POS data of the unmanned aerial vehicle; and fifthly, merging the aerial photography areas according to the fact that the actual altitude difference is smaller than the altitude difference critical value, and finally obtaining an aerial photography area merging set capable of carrying out aerial triangulation calculation together.
The specific implementation process of the method is as follows:
(1) POS data calculation aerial photography measuring area DEM area range
Currently, two types of POS auxiliary aerial triangulation and direct sensor orientation are mainly used for directly positioning the ground target by aviation remote sensing based on a POS system. Ogawa, Dingelin, et al ("Large Angle Tilt imaging aerial Camera to ground target location" [ J ]. optical precision engineering, 2017,25(07): 1714-:
(1.a) data processing: four corner image points O in aerial photography area are selected out to unmanned aerial vehicle POS data in each aerial photography area1、O2、O3、O4Coordinates and relative altitude;
(1, b) determining four ground area ranges by vertical projection according to the POS data of the aerial photography areaAngle O1 ’、O2 ’、O3 ’、O4 ’Coordinates of where (lat)i,lngi,hi) For coordinates and relative altitudes in unmanned POS data, (lat)i,lngiAnd) the ground DEM area range vertex coordinates as shown in fig. 1.
(2) Establishing regular grid digital elevation model of each aerial photography measurement area
After the area range of each aerial photography area DEM is determined, an altitude difference critical value between every two adjacent aerial photography areas DEMs needs to be determined. Firstly, a regular grid digital elevation model is established for an aerial photography area by a point-by-point interpolation method as shown in figure 2, wherein h1,h2…hnRespectively the elevation of each grid in m.
(3) Altitude difference threshold calculation
And (3.a) calculating the elevation of the reference surface of the aerial photography area: calculating the height of the reference surface of the regular grid DEM of each aerial photography area according to an unmanned aerial vehicle altitude calculation formula (3-1) in the Low altitude digital aerial photography Specification;
wherein h isBase ofThe unit is m, and the elevation of a reference surface of the aerial photography area is taken as the elevation of the aerial photography area; h isiThe elevation value of the DEM grid point in the aerial photography area is m; and n is the number of DEM grid points in the aerial survey area.
(3, b) calculating a critical value of the altitude difference between every two adjacent aerial photography areas: when the DEM design is adopted in the low-altitude digital aerial photography specification, the height of the reference surface of the aerial photography area is calculated according to a formula (3-1), so that the height difference of the reference surfaces of the adjacent aerial photography areas is the critical value of the altitude difference, as shown in figure 3. And determining a critical value of the altitude difference between every two adjacent aerial photography areas by using the altitude difference of the reference surface, as shown in a formula (3-2).
Wherein △ h is aerial photographCritical value of altitude difference, h, between survey areas A and BRadical A、hRadical BIs the reference level height of aerial survey areas A and B, nA、nBThe grid number h of the digital elevation model of the aerial photography measurement area A and B respectivelyiAnd the elevation value of each grid of the digital elevation model of the aerial photography area A and B is obtained.
(4) Actual altitude difference between every two adjacent aerial photography regions
(4.a) data preparation: unmanned aerial vehicle POS data of each aerial photography area;
and (4, b) the difference of the relative altitude average values in the POS data of the unmanned aerial vehicles in every two adjacent aerial photography areas is the actual altitude difference.
(5) Aerial survey region collection generation
The method is implemented by merging the aerial regions according to the actual altitude difference of the POS data of the adjacent aerial regions and the altitude difference critical value obtained based on the aerial region DEM, and is mainly divided into four steps, namely ① selecting a starting aerial region, ② the regional range of the aerial region DEM, ③ calculating the altitude difference critical value between the adjacent aerial regions DEM, and ④ merging the aerial regions based on the actual altitude difference calculated by the POS data and the altitude difference critical value between the adjacent aerial regions DEM, and finally obtaining the merging result of the aerial regions.
1) And selecting a starting aerial surveying area. And selecting one aerial photography area as a starting aerial photography area a, and vertically projecting the data of the aerial photography area POS onto an aerial photography area DEM to obtain a ground range A of the starting aerial photography area.
2) And determining adjacent aerial photography areas and DEM area ranges around the aerial photography areas. Determining four-direction aerial photography areas as b, c, d and e according to the initial aerial photography area a, and obtaining the area range of the corresponding aerial photography area DEM in the step 1), wherein B, C, D, E is the area range of the adjacent aerial photography area DEM.
3) The height and the altitude difference of the reference surface of each aerial photography area. The reference surface heights h of the initial aerial photography region A and the adjacent aerial photography region B, C, D, E are obtained by the formula (3-1)Radical A、hRadical B、hRadical C、hRadical D、hRadical EAnd calculating the altitude difference △ h between A and B, C, D, EBase ofIs | hRadical A-hRadical B|、|hRadical A-hRadical C|、|hRadical A-hRadical D|、|hRadical A-hRadical E|；
4) And merging the aerial photography areas. And obtaining the actual altitude difference delta h of the adjacent aerial photography areas according to the relative altitude average value in the POS data of the areas A and B, C, D, E, merging the actual altitude difference delta h with the initial aerial photography area A for aerial triangulation encryption if the actual altitude difference delta h is smaller than the corresponding altitude difference critical value, and not merging the actual altitude difference delta h with the initial aerial photography area A for aerial triangulation encryption if the actual altitude difference delta h is not smaller than the corresponding altitude difference critical value. And (3) determining the aerial photography areas which do not meet the dividing conditions as new initial aerial photography areas, and circulating according to the steps 1), 2), 3) and 4) until each aerial photography area and the combined aerial photography area are used as the initial aerial photography areas, and ending circulation to finally obtain the new aerial photography areas or the original single aerial photography areas after the plurality of aerial photography areas are combined.
The present embodiment will be further described below by selecting the Town of Meishan county, Kinzhai county, Anhui province as a sample area.
First, summary of test area
The area of the aerial photography test area in the town of Meishan mountain, national village of Kinzhai, Anhui province is about 305 square kilometers. Because the mountainous regions of the plum mountain town of Jinzhai county have larger fluctuation degree, the aerial photography is carried out in the town region by adopting orthographic shooting and inclining, wherein the inclining adopts each route to carry out the aerial photography with different camera angles for two times so as to achieve the effect of five cameras; and in the mountainous area with few population, the data acquisition is carried out by adopting an orthographic aerial photography mode.
Second, preparation of aerial photography parameters and data
A self-developed fixed wing drone capable of automatic vertical take-off and landing is used for installing a Sony DSC-RX1RM2 camera, the focal length of the camera is 35mm, the image size is 7952 pixels 5304 pixels, the relative flight height of the flight path is 200-600m, and the heading and the side-by-side overlapping degree are both 80%. And generating a real-scene three-dimensional model for the data processing platform by using the Context Capture4.46. 30m resolution DEM digital elevation model of Town and Town of Mei, Jinzhai county. 20 to strong E5-2609v3, 16G, NVIDIA Quadro M2000 workstation. 214 aerial photography areas, 183 forward aerial photography areas and 31 inclined aerial photography areas are designed according to the cruising ability of the unmanned aerial vehicle and the terrain of the national village, 60125 images are calculated, and the POS data of the complete and partial enlarged aerial photography areas are shown in figures 5 and 6.
Thirdly, by using the data and the merging method, a new aerial photography area after merging of a plurality of aerial photography areas can be finally obtained, as shown in fig. 8.
Claims (1)
1.A method for merging oblique photography non-image control point measurement areas based on DEM is characterized by comprising the following specific steps:
step 1, calculating the regional range of a DEM (digital elevation model) of a measurement area by POS (point of sale) data:
obtaining POS data of unmanned aerial vehicles in each measuring area; screening out longitude and latitude coordinates of four corner image points of a measuring area in the POS data, and determining the longitude and latitude coordinates of the four corner image points in the DEM area range of the measuring area in a vertical projection mode;
step 2, constructing a regular grid DEM of each measurement area:
after the area range of each measurement area DEM is determined, a regular grid DEM of each measurement area is constructed by adopting a point-by-point interpolation method;
step 3, calculating a critical value of altitude difference:
firstly, calculating the height of a reference surface of each measuring area regular grid DEM, wherein the formula is as follows:
wherein h isBase ofThe elevation of a reference surface of a DEM is measured; h isiThe elevation value of the DEM grid point in the measuring area is obtained; n is the number of grid points of the DEM in the measuring area;
then, determining a critical value of the altitude difference between every two adjacent measuring areas by using the altitude difference of the datum plane, wherein the formula is as follows:
wherein △ h is the critical value of altitude difference between adjacent measurement areas A and B, hRadical A、hRadical BThe height of the reference plane of DEM for measuring area A and B, nA、nBRespectively the number of grid points of DEM in the measurement area A and the measurement area B;
step 4, calculating the difference of the relative altitude average values between every two adjacent measuring areas based on POS data of the unmanned aerial vehicle, and taking the difference as the actual altitude difference between every two adjacent measuring areas;
and 5, generating a measuring area merging set: taking a certain measuring area as an initial measuring area, and determining measuring areas adjacent to the periphery of the initial measuring area; if the actual altitude difference between the initial measurement area and the adjacent measurement area is smaller than the altitude difference critical value, the adjacent measurement area can be merged with the initial measurement area, otherwise, the adjacent measurement area is not merged with the initial measurement area, and the adjacent measurement area is used as the initial measurement area again for cyclic judgment until each measurement area and the merged measurement area are used as the initial measurement area; finally, a merging set after merging the measuring areas is obtained, and the measuring areas in the merging set can be subjected to aerial triangulation calculation together.
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