CN104156991A - Airborne digital topographic data compression method for low altitude penetration - Google Patents
Airborne digital topographic data compression method for low altitude penetration Download PDFInfo
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- CN104156991A CN104156991A CN201410376630.9A CN201410376630A CN104156991A CN 104156991 A CN104156991 A CN 104156991A CN 201410376630 A CN201410376630 A CN 201410376630A CN 104156991 A CN104156991 A CN 104156991A
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Abstract
The invention provides a method which combines the surface fitting with a JPEG lossy compression coding technology, applies the technology combining the surface fitting with the JPEG image compression to compression of topographic data in a topographic database and a topographic matching database for real-time route planning and provides an airborne digital topographic data compression method for low altitude penetration. Firstly, surface fitting is performed on small blocks of topographic data after the large-scale topographic data is divided into small blocks of data on the basis of Marquardt, topographic data before fitting is compared with the topographic data after fitting, the residual is calculated and JPEG lossy compression is performed on the residual exceeding safe flying range (-100 m to 100 m) of a plane. The method not only retains the change of the topography, but also reduces the storage space of altitude data of the topography.
Description
Technical field
The present invention relates to Terrain Data Compression technical field, be specially a kind of airborne digital terrain data compression method for low-level penetration.
Background technology
Along with the develop rapidly of modern technical aeronautics, oneself becomes present generation aircraft indispensable important component part in-flight numerical map.And along with the development of remote sensing technology, satellite technology, making to obtain high-resolution digital terrain data becomes possibility.Modern terrain data acquisition technique provides accurate terrain data to people, yet along with more and more higher to the requirement of landform degree of accuracy, the memory space of terrain data is also increasing.On the other hand owing to requiring high especially to the electronic equipment of on-board data storage, must there is high reliability, volume is little, lightweight, shock resistance, anti-vibration, high-low temperature resistant, have the very strong requirements such as environmental suitability, this has just limited the use of general data memory device.Present stage, the memory capacity that can meet the harsh data storage medium requiring of air environment is not height very.
Summary of the invention
The technical matters solving
The compress technique of existing most of terrain datas is in order to meet people's sense organ requirement, to be applied in the research of terrain visualization.Yet, airborne digital map in being applied to Plane Low Altitude Penetration, the compress technique of existing terrain data often can not meet the security requirement of aircraft flight simultaneously, and the terrain data of storing more accurately magnanimity when adapting to airborne storage capacity.
Technical scheme
The present invention combines the method for surface fitting and JPEG lossy compression method coding techniques, technology by surface fitting in conjunction with jpeg image compression is applied in the compression of real-time trajectory planning with the terrain data in topographic database and terrain match database, a kind of airborne digital terrain data compression method for low-level penetration has been proposed, first, the terrain data of the fritter after the landform piecemeal of large scale is carried out based on the matching of wheat quart normal surface, terrain data before and after contrast matching, then calculate residual error, to exceeding the residual error of Flight Safety scope (100m～100m), carry out JPEG lossy compression method.
Technical scheme of the present invention is:
Described a kind of airborne digital terrain data compression method for low-level penetration, is characterized in that: Large-scale Topography altitude figures is carried out to piecemeal, each the fritter landform altitude figures obtaining is carried out processing as lower compression:
Step 1: adopt the wheat quart method in Nonlinear least squares optimization method to carry out surface fitting to landform altitude figures, obtain corresponding elevation function z=f (x, y), (x wherein, y) represent the location point in landform altitude data, z is the Fitting height value that point (x, y) is located;
Step 2: the altitude figures residual error of each point in the elevation function that calculation procedure 1 obtains, if altitude figures residual error a little all in (100m～100m) scope, adopting this surface fitting result is data compression result, otherwise carry out step 3;
Step 3: using the altitude figures residual values of each point as to the pixel value that should put, obtain a two field picture, this two field picture is carried out to the compression of JPEG lossy compression method, obtain data compression result, wherein when carrying out the compression of JPEG lossy compression method, need to make maximum positive and negative minimum to recovering error.
Further preferred version, described a kind of airborne digital terrain data compression method for low-level penetration, is characterized in that: the number of data points in each patch graphic data is the multiple of 8 * 8 pieces.
Further preferred version, described a kind of airborne digital terrain data compression method for low-level penetration, is characterized in that: the number of data points in each patch graphic data is not more than 32 * 32 number of data points.
Beneficial effect
The present invention carries out based on the matching of wheat quart normal surface landform altitude figures, and the terrain data before and after contrast matching, then calculates residual error, to exceeding the residual error of Flight Safety scope (100m～100m), carries out JPEG lossy compression method.The method has not only retained the fluctuations of landform, has also reduced the storage space of landform altitude data.
Accompanying drawing explanation
Fig. 1: image before and after the matching of the altitude figures of subdued topography, (a) landform before matching, (b) landform after matching;
Fig. 2: image before and after the matching of the altitude figures of complex-terrain, (a) landform before matching, (b) landform after matching;
Fig. 3: JPEG lossy compression method compression step;
Fig. 4: the residual plot before and after the compression of JPEG lossy compression method quantizes, (a) raw residual figure, (b) retains the residual plot after 6 quantization of transform coefficients;
Fig. 5: the topomap that initial landform data are combined with surface fitting after JPEG compression recovery contrasts, (a) initial landform figure, (b) compression is schemed after recovering;
Fig. 6: comparison diagram before and after original complex-terrain data compression, (a) initial landform figure, (b) compression is schemed after recovering.
Embodiment
Below in conjunction with specific embodiment, the present invention is described:
What the present embodiment was used is the landform altitude data that in the SRTM3 file of east longitude 108 degree north latitude 34 degree, 32 * 32 points of the smooth and complex-terrain of intercepting form respectively, adopt the altitude figures point of 32x32, be to obtain better compression effectiveness for residual error being carried out to JPEG lossy compression method below on the one hand, it is the multiple of 8 * 8 pieces that the altitude figures of choosing is counted; Adopt on the other hand the altitude figures point of 32x32 can meet the requirement of this proof of algorithm of analysis, also can adopt according to actual needs the altitude figures piece of other 8 * 8 multiples.
First adopt the wheat quart method (Levenberg-Marquardt) in Nonlinear least squares optimization method, multiplicity is 30, and controlling number of iterations is 20.Landform altitude figures is carried out to surface fitting optimization calculating, obtain optimal parameter, the coefficient of determination, root-mean-square error etc.Altitude figures before and after contrast matching, obtains residual error.For example, establish x and represent the point of 32 on east longitude, y represents the point of 32 on north latitude, and z is the height value on these aspects.By said method, try to achieve function f, make z=f (x, y).
In Fig. 1, be mainly the matching front and back image of the altitude figures of subdued topography, although have a lot of little corner angle before matching, to whole landform tendency, there is no too much influence.Height value residual error negative value minimum after matching be-4m, and on the occasion of being 11 meters to the maximum, within the safe range (100m～100m) of aircraft and do not affect the whole landform tendency of understanding, residual error can be left in the basket.The fitting formula of Fig. 1 is:
Root-mean-square error is 3.57.
The landform that Fig. 2 is variation more complicated, fluctuation ratio is larger, height value residual error before and after matching differs too large, between-216-268, exceeded the safe flight scope (100m～100m) of aircraft in low-level penetration, so these residual errors can not be left in the basket, must do JPEG lossy compression method to them, retain these useful residual error data.As can be seen from Figure 2 after matching, the large corner angle feature in topographic relief has all polished, and has occurred distortion.The fitting formula of Fig. 2 is:
Root-mean-square error is 84.81.
Because residual error is that landform altitude data new after our curve are than former data or high or low, for the larger landform of fluctuation ratio, height value residual error before and after matching differs too large, exceeded the safe flight scope of aircraft in low-level penetration, the point that we need to obviously exceed original altitude figures these reduces coordinate, to being starkly lower than the point of original altitude figures, improve coordinate, exactly the corner angle of residual image are done to suitable scabbling, make like this embodiment initial landform altitude figures of the real result that finally obtains.Here the pixel in image using the residual error after matching, carries out the compression of JPEG lossy compression method, and compression step is as Fig. 3.
Present stage, JPEG lossy compression is widely used in compression of images field.In airborne digital map, terrain data residual error in penetration area territory is stored with partitioned mode, every terrain data residual error is the data matrix of grid configuration, so plot shape residual error data can analogize to a two field picture, and its altitude figures is corresponding with image slices vegetarian refreshments.In low-level penetration, altitude figures is recovered error can affect flight safety, so will control and make during JPEG lossy compression method maximum positive and negative minimum to recovering error.
As shown in Figure 3, JPEG lossy compression method compression is that the residual error data after curve is carried out to dct transform, be residual error data from original space field transformation closely related to one another for statistics each other comparatively separate, even reach completely independently domain of variation matrix of coefficients.In order to obtain better compression performance, the residual error data of curve is 32 * 32 points, it is divided into 8 * 8 some piece, each 8 * 8 residual error data is carried out to dct transform successively, according to the different requirements of the residual error data to after rebuilding, the conversion coefficient after dct transform is carried out to different quantifications.After orthogonal transformation, energy mainly concentrates on the minority coordinate in new coordinate system.Finally, the residual matrix after quantizing is carried out to Huffman coding.Cost fun ction data are carried out entropy decoding and idct transform to residual error exactly.
According to the data demand after airborne digital map compression recovery, obtaining the necessary security of considering aircraft flight simultaneously of good ratio of compression.Quantize to choose the residual error of the conversion coefficient that retains 6, landform altitude figures is recovered.Fig. 4 (a) is the residual plot before compression, and Fig. 4 (b) is for retaining the residual plot after 6 quantization of transform coefficients.Can find out that, under the prerequisite maintaining the original shape, higher residual error has been lowered, lower residual error has been raised.
Contrast the topomap that initial landform data are combined with surface fitting after JPEG compression recovery.As Fig. 5, the method for the present embodiment has not only retained the fluctuations of landform, has also reduced the storage space of landform altitude data.
Table 1 has contrasted the compression performance in conjunction with surface fitting and JPEG Lossy Compression Algorithm and simple JPEG Lossy Compression Algorithm.Recover the data through surface fitting and JPEG lossy compression method, maximum positive error before and after the compression of landform altitude data is 80.6 meters, maximum negative error is-58.1 meters, all within the safe range of aircraft, ratio of compression can reach 3.78, if only this landform altitude figures is carried out to JPEG lossy compression method, the prerequisite lower compression of identical quantization matrix is 2.24 than only.
The compression performance of table 1 this paper compression method and JPEG lossy compression method
Fig. 6 is the landform of complex-terrain relatively, is by the comparison diagram before and after the Terrain Data Compression being spliced of 9 32 * 32.Fig. 6 (a) is initial landform figure, and Fig. 6 (b) is for compressing the topomap after recovering.In 9 initial landform figure, there is the topomap of 2 32 * 32 meeting under the prerequisite of aircraft safety area requirement, can only to terrain data, do surface fitting, other 7 blocks of data have been applied algorithm herein, have greatly reduced data and have taken up space.The positive vertical error of maximum before and after compression is 70.68, and maximum negative vertical error is 60.27, and ratio of compression is 4.22.
Claims (3)
1. for an airborne digital terrain data compression method for low-level penetration, it is characterized in that: to Large-scale Topography
Altitude figures is carried out piecemeal, and each the fritter landform altitude figures obtaining is carried out processing as lower compression:
Step 1: adopt the wheat quart method in Nonlinear least squares optimization method to carry out surface fitting to landform altitude figures, obtain corresponding elevation function z=f (x, y), (x wherein, y) represent the location point in landform altitude data, z is the Fitting height value that point (x, y) is located;
Step 2: the altitude figures residual error of each point in the elevation function that calculation procedure 1 obtains, if altitude figures residual error a little all in (100m～100m) scope, adopting this surface fitting result is data compression result, otherwise carry out step 3;
Step 3: using the altitude figures residual values of each point as to the pixel value that should put, obtain a two field picture, this two field picture is carried out to the compression of JPEG lossy compression method, obtain data compression result, wherein when carrying out the compression of JPEG lossy compression method, need to make maximum positive and negative minimum to recovering error.
2. a kind of airborne digital terrain data compression method for low-level penetration according to claim 1, is characterized in that: the number of data points in each patch graphic data is the multiple of 8 * 8 pieces.
3. a kind of airborne digital terrain data compression method for low-level penetration according to claim 2, is characterized in that: the number of data points in each patch graphic data is not more than 32 * 32 number of data points.
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| CN105790771A (en) * | 2016-03-29 | 2016-07-20 | 黄河勘测规划设计有限公司 | 3D topographic data compression method of superhigh compression ratio |
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