THE ASSESSMENT OF ORTHOPHOTO QUALITY WITH RESPECT TO THE STRUCTURE OF DIGITAL ELEVATION MODEL |
Paper ID : 1098-SMPR-FULL |
Authors: |
مژده ابراهیمی کیا *1, مهدی مدیری2, حمید عنایتی2 1تهران خیابان سی متری نیروی هوایی میدان لوزی خیابان 9.31 پلاک3 2جغرافیایی |
Abstract: |
Orthophoto is an image which is being corrected geometrically and each object has to be situated on the corrected place consequently. Having geographical and radiometrical data together made the high number of Orthophoto usages in prior stages of most engineering plans which have caused to have more attention to both of the geometric and quality aspects. In this paper after passing a review of generation of orthophotos and its necessary steps and factors like as georefrencing procedure and digital elevation model (DEM), we have focused on DEM structure influences on the quality and precision of orthophotos. For showing the effects of applying a suitable DEM structure on removing of the most height differences of captured images, we have tried to apply some unreasonable resolution of digital elevation model (DEM) in orthophoto producing and results of them have shown respectively. Choosing the best DEM structure with respect to the area topographic is the most challenge which has more important role when dealing with rough surfaces displacements in duration of orthophoto procedures. The Lower DEM resolution makes points density lower and makes the procedure faster but cause to decreasing the product precision in compare to choosing the other one. However if a fine resolution DEM cause to very delicate displacement corrections aside of the other benefits but it makes to appear some undesired visualized errors like as elongation error especially in an areas which are hidden with some obstacles and there are lacks of data in an imaging. For preventing of such error in DEM structure calculation and earning the most benefits, we found and execute some solutions. In other word we answered to this question that what DEM resolution is the best for orthophoto production. In the following we have done some tests. First a dense DEM of a topographic area calculated and edited accurately then its density was reduced in some steps gradually. At each stage the root mean square error (RMSE) of interpolated heights of points which were laid in the distance between the corresponding DEMs pixels has been calculated respectively. Two interpolation methods (Nearest neighbour and Bilinear interpolation) have been used in this test. Decreasing the DEMs density or increasing the pixel size made the amounts of errors high and the rate of this changing dependent on the kind of topography directly. So we divided the area into some reasonable topographic classes then calculated our results for each class separately. The result of each strategy presented in both numerical tables and some illustrated images and compare with each other. Because of the relation between horizontal precision of orthophotos which are defined from the existing standard producing instruction and the accuracy of the DEM which are mostly related to its density, the suitable resolution for producing different scale orthophotos at each kind of topographic class have been calculated from mentioned methods consequences and shown as a final result. |
Keywords: |
orthophoto, height displacement, orthophoto elongation, Orthophoto precision, Orthophoto quality, DEM structure |
Status : Paper Accepted (Oral Presentation) |