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how_to_create_dem [2017/05/15 19:34] efox created |
how_to_create_dem [2017/05/15 20:49] (current) efox |
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| - | ====== | + | ====== |
| * **limited number of points** | * **limited number of points** | ||
| * on-ground surveys | * on-ground surveys | ||
| * total station or GPS | * total station or GPS | ||
| + | * Assuming a correct use of the instruments and the post‐processing computer tools, the MDEs generated with these data will have high accuracy | ||
| * indirect methods | * indirect methods | ||
| * photogrammetry | * photogrammetry | ||
| Line 13: | Line 14: | ||
| * indirect methods | * indirect methods | ||
| * cross-correlation photogrammetric methods | * cross-correlation photogrammetric methods | ||
| + | * comparison of digital images from stereoscopic pairs of digitized aerial photographs | ||
| + | * There is a wide variety in DEM accuracy depending on the flight' | ||
| * Structure from Motion | * Structure from Motion | ||
| + | * Photogrammetric techniques that allow, starting from conventional photographs not calibrated: | ||
| + | * obtain the position of cameras and the angles of correlations | ||
| + | * obtain maps of disparity (paralax) | ||
| + | * get a cloud of high density points | ||
| + | * generate DSM | ||
| + | * final objective is to determine a 3D model of the terrain | ||
| * RADAR interferometry | * RADAR interferometry | ||
| * digital cartography | * digital cartography | ||
| - | ==== total station or GPS ==== | ||
| - | * Assuming a correct use of the instruments and the post‐processing computer tools, the MDEs generated with these data will have high accuracy | ||
| - | ==== cross-correlation photogrammetric method | + | ====== algorithms for SfM====== |
| - | * comparison | + | * SIFT (Scale Invariant Feature Transform) |
| - | * There is a wide variety | + | * for detection |
| + | * It aims to find relevant features | ||
| + | * We extract the elements in the spatial and frequency domain that have invariance | ||
| + | * For each obtained point a descriptor is generated and is used to match the elements found in each one of the individual images | ||
| + | * By mapping points between images, the 3D position of the point is determined | ||
| + | * detection of endpoints | ||
| + | * Descriptor SURF (Speeded-up robust features) | ||
| + | * Enhanced computational performance using a Hessian matrix and an integral image descriptor. Is several times faster than SIFT and more robust against different image transformations than SIFT | ||
| + | * ASIFT (assine SIFT) | ||
| + | * Determines invariant points with SIFT when performing affine transformations | ||
| + | * PCA-SIFT | ||
| + | * Variation of SIFT against changes of illumination and that reduces | ||
| + | * GLOH (Gradient Location‐Orientation Histogram) | ||
| + | * Calculate SIFT for the regions resulting from 3 divisions in the radial direction | ||
Permalink how_to_create_dem.1494869698.txt.gz · Last modified: 2017/05/15 19:34 by efox
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