Research On Ortho-differential Correction Of Low-altitude UAV Images In Areas With Large Terrain Undulation

With the advancement of digital remote sensing technology,in addition to more advanced remote sensing satellites can provide high-definition satellite images,the low-altitude UAV also can provide high-resolution remote sensing image easier and faster.the high-resolution remote sensing image can be processed into high-resolution orthophotos,which has advantage in the amount of information intuitiveness,Current potential and position information.Therefore,the orthophotos is more and more used depending on different needs,high-resolution orthophotos were used in Land Bureau,Planning department,Surving and Mapping,Emergency Relief and other departments to provide different information.Some departments care high positioning accuracy,but other departments are more concerned on other information.Surving and Mapping industries focus on the position accuracy of high resolution orthophotos most,high-resolution orthophotos can be used to update the previous mapping Products and review the integrity of mapping products come from other measure ways.according to different requirements,Different types of thematic maps with relatively high position accuracy can be extracted from othrophotos.In rugged area,Practice has proved that in flat areas orthophotos form UAV has a better position accuracy than rugged area.That’s mean the position accuracy of high-resolution orthophotos is relatively low in undulating terrain area,which limits the further use of orthophotos in Surving and Mapping.After a comprehensive considering of the entire production process of UAV orthophotos,This article introduced factors which will affect the accuracy of orthophoto maps,such as lens distortion,feature extraction and matching,relative orientation,absolute orientation,and the impact of DEM in detail.The feature point matching,absolute orientation adjustment accuracy and DEM were highlighted and carried experimental analysis.A deep study was carried on how DEM affects UAV orthophoto map accuracy and how to reduce the error in undulating area.when filtering the noise point in DEM point cloud,a reverse engineering software Geomagic Studio 12 is used to process entire measurement area.