GISdevelopment.net ---> AARS ---> ACRS 1990 ---> Mapping From Space Analytical method for GIS basic data acquisition Li Deren, Ge Renyan, Wang Shugen Wuhan Technical University of Surveying and Mapping, Wuhan, China Abstract The good base height ratio and high space resolution of SPOT imagery make it possible to be handled on analytical photogrammetric instruments. After a brief analysis of the geometry of SPOT imagery and a series investigation of software system of PLANICOMP analytical plotter, an analytical plotting software package of POST imagery at c-130 and a software for the production of orthophotoes from SPOT imagery on Orthoprojector OR-1 have been developed. Using the panchromatic SPOT stereo pair over the area of Marseille in the south of France, some experiments have been carried out. A topographic map of 1:50,000 scale has been on c-130 analytical. According to the residuals in 32 check points the means square errors in X, Y an Z coordinates are dx +5.4m, dy +7.1m, dz +5.5m which can meet the accuracy demands of 1:50,000 map in mountain areas. A 1:50,000 orthophoto of SPOT imagery has been also produced by using OR-1. The mean square error of position in orthophoto is +0.29mm which fairly meets the requirement of 1:50,000 map. Because of two time duplication the object resolution of SPOT imagery was not so good. The whole investigation shows that mapping from space would be available and effective. Introduction One of the important basic data for Geographic Information System (GIS) from 1:50,000 & 1:100000 scale topographic maps. Therefore, the mapping of these scale maps from SPOT imagery, which gives us a very high geometric accuracy, is becoming a world widely concerned problem at present. Some European countries' research works show that mapping and map revision can be accelerated using the SPOT satellite images. The map revision cycle can be reduced to 2-3 years for 1:50,000 map and only 1 year for 1:10000 map. To the area where no maps have been made, the stereo observation ability and high resolution of SPOT imagery can supply with the about 10 meters demand of middle elevation accuracy, and with the plane accuracy of 10-20 meter which can meet demand of middle scale mapping productions. Besides these, SPOT images can also be used for producing orthophotoes and other thematic maps. The work cab be done by using modern analytical photogrammetric instruments, so long as the corresponding software are developed. Method for calculation of exterior orientation elements According to the geometry of SPOT imagery, the calculation of exterior elements had some different methods. For example, the bundle adjustment, the processing method of frame central projection, and the processing method of line central projection. All above methods have obtained some satisfied results, but if these processing methods are used for the calculation of orientation elements on analytical plotter PLANICOMP c-130 some problem will rise. For instance, the required amount of internal storage is too large, the calculation speed is slow and the obtained exterior orientation elements are not corresponding with the orientation parameters of analytical plotter etc. in this paper, a space resection method which is suitable for the calculation of exterior orientation elements from SPOT imagery on analytical plotter is submitted . According to the ground control points read out fro, old maps, and the related image coordinates measured on analytical plotter, the exterior orientation elements can be obtained using the phogrammetric method of space resection. In order to overcome the strong correlation among exterion orientation elements of SPOT images, the repeated iteration method is adopted to calculate the linear elements and angular elements separately. The formula for solving exterior orientation elements come from collinearity equation of SPOT image. The first step is to solve linear elements by the use of following error equations. Vxi = a14DXs0 + a15DYs0 + a16DZs0 + a14yiDk4 + a15yiDk5 + a16yiDk6 - Ixi Vyi = a24DXs0 + a25DYs0 + a26DZs0 + a24yiDk4 + a25yiDk5 + a26yiDk6 - Iyi Then, the second steps is to solve angular elements according to the following error equations : Vxi = a11Dj0 + a12Dw0 + a13Dk0 + a11yiDk1 + a12yiDk2 + a13yiDk3 - Ixi Vxi = a21Dj0 + a22Dw0 + a23Dk0 + a21yiDk1 + a22yiDk2 + a23yiDk3 - Iyi Where a11 = -(x2cosk/f + f* cosk)cosw a12 = -(f + x2f-1)sinkcosf0 a13 = 0 a14 = (a1f + a3x)/Z a15 = (b1f + b3x)/Z a16 = (c1f + c3x)/Z a21 = -x sinw + f sinkcosw a22 = -f cosk a23 = -x a24=a2f/Z a25=b2f/Z a26=c2f/Z in which Z=a3(x1-Xs1) + b3 (y1-Ys1) c3(Z1-Zs1) Above procedures are iteratire After the exterior orientation elements are obtained, we transform them and their change rates into the model coordinate system of analytical plotter. The transformed values can be used directly as the orientation parameters for the plotting of SPOT image on analytical plotter. The plotting software system of spot imagery The system program and the service program of analytical plotter are developed based on the photgrammetric frame central projection. In the real time circulation program, (Loop program) of the system, the image point and the object point are corresponded each other according to the well known collineraity equation. Because the SPOT image is composed of 6000 lines linear central projection image instead of place central projection, the normal Loop program, cannot be directly used. To solve this problem, the line-sean geometry of SPOT imagery must be considered and the exterior orientation elements of SPOT image should be line by line changed in real time in order to meet the need of corresponding relation of image point with object point I original Loop program, but actually, this not possible or it is very difficult to realize such change. To solve this problem, a modified method using stereo correction grid is suggested Konecny. According to his thought, the original Loop program is interpolated with a real time grid correction program, which is executed co-ornately with original Loop program. When the measuring mark is moving according to the principle of central projection, an additional movement is taken in order to satisfy the projection principle of central projection principle of SPOT imagery. According to this principle, it will not be too difficult to realise above purpose on the series o available analytical plotter PLANICOMP. The detailed procedures will be demonstrated through fig.1 and fig. 2. According to this procedure it is very easy to introduce the corrections of image stage coordination into the Loop program in real time. The rigorous relationship between object and image point of SPOT imagery can be ensured. 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. Then the image profile data can be calculated according to collinearity equation, this is also a repeated iteration process. The generated image coordinate date can be stored on tape with the standard format demand by OR-1. for this purpose a special software has been developed. The left image of Marseilles stereo pair was chosen for test. DEM is red out from topographic map with the scale of 1:25000. The image exterior orientation elements are taken from the adjustment results in chapter 2. In order to check the program, twenty ground control points were chosen in the experiment area, with the comparison of the measured and calculated image coordinates, the mean square errors of coordinate differences are obtained as : mDx = ± 10.9mm mDy = ± 12.2mm This accuracy is good enough for the production of 1:50,000 orthophoto from 1:400000 SPOT imagery with the magnifying factory of 8. Using the above obtained image profile data, a orthphoto with the scale of 1:50000 in test window (produced from transparent positive) is produced with the slit length of 5mm (see fig.4). After the comparison with existing map the position accuracy on orthophoto is about 9+10.29mm in map scale, which meets the demand of orthophotos. Summary The analytical plotting software system of SPOT imagery on PLANICOMP C-130 has been developed, a test of the plotting of a 1:50,000 topographic map shows that this system has a good stability. This program has now been installed on PLANICOMP C-120 and C-130 at research institution and production units. He software for production of SPOT orthophotos from DEM at OR-1 has been also developed. Now we will continue the further research work in order to make contribution for the data acquisition of GIs from space by the use of available analytical plotter and orthoporjector. References Wang Zhizhou principle of photogrammetry (the sequel) press of surveying and Mapping 1986. Li Deren : Bundle Adjustment of SPOT imagery Acta Geodetica et Cartographic Sinica, 1988, No. 3 Xiu Miaozhong : Developing of Analytical plotter function and satellite Mapping software system, Master thesis at WTUSM, 1988 Konecuy, G.et.al : Evaluation of SPOT imagery in Analytical photogrammetric Engineering and remote Sensing, Vol 53, Sept. 1987 Li Deren et al: Analytical photgrammetric evaluation of SPOT imagery, Journal of WTUSM 1988, No. 4 Ge Renyan: Space Resection method for the calculation of Exterior Orientation elements on Analytical plotter C-130, Bulletin of Survey and Mapping, May 1988. Chang Benyi: Test for the stereo plotting of SPOT imagery, 1988, Xian G. Picht: The processing of SPOT imagery on analytical PLANICOMP, Seminar on SPOT image evaluation, Hannover 1987 Xiao anbo; simple introduction for the plotting application of SPOT satellite. Science and technology of surveying and Mapping 1998, No.2 Wang shugen: The production of orthophoto from SPOT imagery at OR-1 Bulleting of suveying and mapping, 1990 No. Fig.3 Topographic map based on spot image. Fig.4 Orthophoto of spot image.