Analytical method for GIS basic data acquisition
To c-130 the execution of Loop program, which has be cycle of 20milli second, takes about 1-9 ms, so if the new added real time grid correction program can be completed within 10 milli-seconds, there is no problem to realize above method. Some test has shown that it actually take 6 milli-second, for the running of real time grid correction program(B154) on the A600 Computer of HP1000 series. Obviously, the system can work well in a cycle of so time/second. Since the real time plotting program B154 belongs to
Class-B program, and the plotting table on orientation program (TABLE ORIENTATION) in the original service program also belongs to class-B the program B154 will be broken when the original plotting table orientation program is executed, which makes the orientation uncompleted. In order to solve this problem, starting from the original program, we use the relationship between model coordinate and plotting table coordinate as well as the relationship between model point and the point draws on plotting table, to calculate each parameter in T matrix, and then put them into common parameter block. In this way the plotting table orientation will be completed.
This software system has been developed successfully on analytical plotter PLANICOMP c-130, and it can be also be run on A600, A700 and A900 computer equipped with C-120, C-100, analytical plotter.
Fig.1 Plotting software system for SPOT images
Fig.2 Relationship between Loop and B154 Program
Test results for the plotting of 1:50,000 topographic map
For the test, a panchromatic spot stereo pair over the area of Marseilles in South of France is used. A part of the plotted 1:50,000 topographic map is shown in Fig. 3 which corresponds to a small window of SPOT stereo pair.
According to the residual, in 32 check points, the mean suare errors of x-, y- and z- coordinates re :
dx = ± 5.4m,
dy = ± 7.1m,
dz = ± 5.5m respectively the planimetric error of object point reading on map is ± 10.25mm, which meet the accuracy demand of 1:50,000 topographic map in mountain area.
Since the scale of spot imagery is too small and the magnifying ration for the plotting of 1:50,000 topographic map is too large, the stereo view of SPOT imagery is not so comfortable as that of areophotograph. An experienced operator is required in this case.
The SPOT images used in this test is obtained through to times duplication, so the identifiability of many ground objects except linear objects is poor, even though the geometric accuracy is still good. Therefore, we can't conclude whether SPOT imagery is suitable for the map revision of 1:50,000 scale or not. Moreover, the left and right image of SPOT stereo pair are obtained from two different obits, there may be a long time difference between them, which will make stereo view difficult.
Therefore a further comparison of SPOT images and line CCD-linear array images is meaningful.
Orthophoto production of spot image by OR-1
The orthoproject OR-1 is and projection transformer controlled by a computer and it takes a small line element (slit) as the unit of differential rectification. The principle of differential rectification at OR-1 is to fulfill the relationship of projection transformation in two end points of each slit. Ti can be used not only for the transformation frame central projection to orthoprojection, but also from the line central projection to orthoprojection. The key for producting SPOT orthophoto is to develop a software to produce POST image profile data from DEM and exterior orientation elements of SPOT image.
The moment exterior orientation of SPOT image can be obtained from a bundle adjustment or a space resection of SPOT imagery. The digital elevation model (DEM) of the corresponding area can be obtained by the manual or automatic measurement with SPOT stereo pair at analytical plotter or directly read out from the existing contour map.
