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Digital Terrain Model producing and processing procedure |
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procedures of producing DTM has been divided into 3 categories: |
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| Producing methods |
Data source |
Extent |
Advantages and disadvantages |
| digitizing existing maps |
digitizing the contour lines in large scale maps. |
extensive area with few terrain changes. |
High accuracy and less equipment, but the data might be changed due to time factor. |
| Ground surveying |
Field surveying |
small region |
Highest accuracy, but time-consuming |
| Photogrammetry and Remote Sensing |
Stereo measuring in stereo pairs on an analytical plotter
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large area |
High accuracy, and high timeliness data |
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Procedure of producing DTM |
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A. |
Use two appropriate aerial photos with 60% overlaps
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B. |
Input interior orientation parameters in two images including focal distance and principal points.(determined by measuring frame mark) |
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C. |
Measuring exterior parameters: After measuring the control points and the positions of the junction points in two adjacent images, we use Space Resection method to calculate the position and orientation parameters while snapping. |
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D. |
From automatic matching conjugate points in two images, we calculate the x parallax with position and orientation parameters in Collinear Condition Equation to solve the 3D position pixel by pixel. |
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E. |
Interpolating these points to regular grid data. |
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