Application And Accuracy Analyse Of Layouting Control Points Based On GPS-supported Aerial Triangulation Topographic Mapping In 1:2000

In the traditional photogrammetric survey block adjustment,the transformation from the aerial triangulation network to the specified ground coordinate system and the absolute orientation of the model net,as well as the correction of the system error are realized by using a lot of ground control points.However,it's difficult to find the suitable ground control points in places like lush but steep mountainous region and hilly areas.Thus,using this method will cause the inefficient and low accuracy of aerophotogrammetric mapping.Therefore,it's important to find a method to reduce or even eliminate the number of ground control points to realize aerial triangulation.In theory,POS-assisted aerial triangulation can realize model aerial survey mapping without ground control points.But in fact,it's hard to meet the accuracy requirements of large-scale aerial photography in actual engineering.In addition,the accuracy may decrease or even unable to meet the requirements as the area of the subarea increases.This paper describes how to find a reasonable image control scheme to meet the accuracy of large-scale mapping in POS-assisted aerial triangulation practice.First,choosing an image control scheme of“4 flight and 15 baseline”and the other scheme of“four-corner elevation point and two-row elevation point”which meet the accuracy requirements to pre-test in Hengshan surveying area.By using Imagination software and Inpho software,it's able to carry out three encryption methods,then compare and analyze the result to explore the indoor work,outdoor work and the image accuracy.Taking the project of digital city of Liling as an example,using the scheme of“4corners of the layout of a flat peak×2 row height control points”and POS-assisted bundle block adjustment,it's possible to figure out the maximum reasonable size of aero-triangulation area which meets the criteria under four different aerotriangulation areas:800km~2,1000km~2,1200km~2 and 1500km~2.Meanwhile,it can be compared with the outside work of conventional bundle block adjustment.The main research achievements are as follows:1.Both internal and external accuracy meet the specific requirements under the image control scheme of“4 flight and 15baseline”by using Imagination software and Inpho software.The block connection of this method is better and universal than the image control scheme of"four-corner elevation point and two-row elevation point".2.By using POS-assisted bundle block adjustment,a flat peak(or elevation point)will be set in each encrypted partition on the four corners.Besides,the control layout scheme of laying two vertical architecture routes in the area of 800km2~1200km2is for meeting the accuracy requirements of large-scale mapping.Adding image control points in the break of route in the encrypted partition of 1500km2can help to make the result meet the accuracy requirements of aerial triangulation.Meanwhile,the supplementary flight route will have a deep impact on the elevation accuracy.It should be no more than 2 supplementary flight routes in one encrypted partition.3.For long and narrow encrypted partition with lots of baselines but less routes,the scheme of"four-corner elevation point and two-row elevation point"can reduce the number of ground image control points effectively to improve the efficiency.