外文翻译 - 图文(4)

1）For test 1，densified points’horizontal accuracy and vertical accuracy are better than 0.15 meter, totally meeting the accuracy requirement: 0.25 meter in planimetry and 0.30 meter in height

[11] of 1:500 Topographic Maps Specifications for

Aerophotogrammetric Office Operation for flat land.

2) For test 2, densified points’horizontal accuracy is better than 0.15 meter and vertical accuracy better than 0.20 meter, totally meeting the accuracy requirement: 0.35 meter in planimetry and 0.40 meter in height

[11] of 1:500 Topographic Maps

Specifications for Aerophotogrammetric Office Operation for mountain land. 3) For test 3, densified points’horizontal accuracy is better than 1 ．1 meters and vertical accuracy better than 1.0 meter, totally meeting the accuracy requirement: 2.5 meters in planimetry and 2.0 meters in height

[12] of 1:5 000 Topographic Maps

Specifications for Aerophotogrammetric Office Operation for mountain land. 4) For test 4, densified points’horizontal accuracy is better than 3.0 meters and vertical accuracy better than 1.5 meters, totally meeting the accuracy requirement: 17.5 meters in planimetry and 3.0 meters in height

[13] of 1:50000 Topographic Maps

Specifications for Aerophotogrammetric Office Operation for high mountain land. It can be seen from Table 2 that for the images of different land types at different scales, the densified points obtained from standard AT and GPS-support AT both satisfied the requirement of 4D product, and that the accuracy of exterior orientation elements obtained by these two methods are generally similar.The larger the photo

scale is, the higher the accuracy of the photo's linear elements we can get; but the accuracy of the photo's angular elements has nothing to do with the photo scale but is related to the focal length of the camera, so the shorter the focal length is,the higher the photo's angular elements accuracy is.Additionally, by comparing the data in Table 2, it can be found that the exterior orientation elements provided by POS system perform are worse than that of analytic aerotriangulation, and also obviously worse than the POS nominal accuracy

mx?my?mz?0.1m，

m??m??18??，

mk?36??.

3.3 Accuracy of direct georeferencing

Currently, 4D product commonly uses the densified points acquired by aerotriangulation as the model orientation points instead of reconstructing the stereo model directly from the image exterior orientation elements．So the accuracy requirement of exterior orientation elements is not defined in the current norm. Generally speaking, so long as enough densification points meet the error threshold limit for each model can we get; by performing absolute orientation,a measurable model which can be reconstructed.Then we can acquire satisfying spatial information. We analyzed the accuracy of direct georeferencing by using different exterior orientation elements, which is calculated by the approach that firstly employ forward intersection

[14], by using the six exterior orientation elements with different accuracy

obtained in the above section, to compute the ground coordinates, and calculate the RMS of ground coordinates of object points (seeing Table 3 for detail) by comparing the ground coordinates with those of most GCPs.

From Table 3，such conclusions can be summed up as follows：

1）For test 1，the horizontal accuracy of direct georeferencing is better than 0.25 meter and vertical accuracy better than 0.15 meter, which well meet the requirement specified in 1:500 flat land terrain mapping standards：0.3 meter in plane and 0.2 meter in elevation

[11].

2) For test 2, the horizontal accuracy of direct georeferencing is better than 0.3 meter and vertical accuracy better than 0.2 meter, which well meet the requirement specified in 1:500 mountain terrain mapping standards：0.4 meter in plane and 0.5 meter in elevation

[11].

3) For test 3，the horizontal and vertical accuracy of direct georeferencing are both better than 1.5 meters, which well meet the requirement specified in 1:5000 terrain mapping standards：3.75 meters in plane and 2.5 meters in elevation

[12].

4) For test 4, the horizontal accuracy of direct georeferencing is better than 3.15 meters and vertical accuracy better than 3.75 meters, which well meet the requirement specified in 1:50 000 downland terrain mapping standards：25.0 meters in plane and 4.0 meters in elevation

[13].

It can be learned from Table 3 that the aerotriangulation approach performs better than POS in obtaining exterior orientation elements when direct georeferencing is applied to images with different land types and scales.This result indicates that using the exterior orientation elements acquired by the aerotriangulation method to perform direct georeferencing can satisfy the accuracy standards of topographic surveying. So it can be deduced that so long as aerotriangulation meets the accuracy standards, the exterior orientation elements derived from that can be used absolutely for producing 4D product.

3.4 Y-Parallaxes in reconstituted stereo models

In the work of photogrammetry, another issue we should pay attention to is the feasibility of directly reconstructing the stereo model for terrain mapping with exterior orientation elements used, that is Y-parallax of model point is not beyond 20 m

[11?13]. So three stereo pairs depicting different terrain types are chosen from four

tests respectively to reconstruct stereo model using the obtained exterior orientation elements

[15], and Table 4 is the Y -parallax on stereo model's corresponding points.

From Table 4, it can be seen that when using the exterior orientation elements obtained by the method of aerotriangulation to reconstruct stereo model, no matter

what type of terrain is applied and how much the scale is, the model points’maximum Y-parallax lies in one pixel and the RMS of that is below half a pixel, which satisfies the accuracy requirement of terrain mapping that vertical parallax's RMS of each model should not be beyond 20 m. But when we use the exterior orientation elements provided by POS, the vertical parallaxes of each model point are all slightly larger, and the smaller the photo scale, the larger the vertical parallax, completely not meeting the requirement.

4 Conclusion

It can be shown from the experiment that, if the elements of the exterior orientation obtained from aerotriangulation meet the accuracy standards, they can be used directly for image orientation and stereo model reconstitution. However, because of systematic errors in POS exterior orientation elements, it is currently difficult to meet the standards of photogrammetry, especially when extracting 3D spatial information. It was found that, in the time of digital photogrammetry, much work can be done automatically by computers, with the reliance on GCPs lessened gradually, thus simplifying operational photogrammetry. On the whole，standard AT, which is the most established and widely-used approach to obtain image orientation parameters, is still the main body of photogrammetry; GPS-supported AT is the easy-to- operate and low- cost method and corresponding standards have been drafted for it; POS direct georeferencing is one of the important cutting-edge techniques in photogrammetry. The basic spatial information acquisition should take advantage of this, and design good plans to gain maximum financial benefits. We propose that, for large-scale mapping of flat areas with good transportation, standard AT should be employed

primarily; for difficult areas, non-charted areas or areas that are not accessible, GPS-support AT without GCPs can be adopted to acquire the basic spatial information for producing national base maps; POS photogrammetry can be used for the production of orthophotos and update of 4D products in small regions．However, POS has a promising prospect in the field of large-scale urban mapping, LIDAR, and digital aerial photogrammetry. We should promote the integration technology of POS system and other sensors by undertaking large- scale experiments, thus providing technical support for economical and rapid gathering of geospatial information. Acknowledgement

The experiment data acquisition are supported by Institute of Remote Sensing Applications Chinese Academy of Sciences, Zhong Fei General Aviation Company, Liaoning Jingwei Surveying & Mapping Technology INC, Dalian Urban Surveying Design Institute, Siwei Aviation Remote Sensing Co. Ltd., Xi'an National surveying＆Mapping Aviation Remote Sensing Co. Ltd and so on. These supports are gratefully acknowledged. The author would like to express his hearty gratitude to Fu Jianhong, Xie Chou, Ji Shunping and Yang Ming for participating in partial experiments. The author would like to thank Yang Ming and professor Zhang jingxiong for their polishing in English. References

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