We create digital elevation models from Topo sheets by extracting the contours. The files are delivered in USGS ASCII format. Topographic maps of various scales are used to extract only contours. If the scans are of good quality the contours are extracted automatically using software’s such as Adobe Photoshop. The extracted contours will be vectorized automatically using proprietary software Viz., LT4X.The extracted contours are edited for achieving continuity in the contours. Once the contours are vector edited they were attributed for proper elevations taking note of the terrain and the availability of Hydro and spot elevations. The dems will be generated in LT4X software as per the projection specification provided.

DEMS were edited in a software viz., Delta3d. Proper care will be taken to include hydro features by specifying the elevations for the Lakes, ocean features etc., Rivers will be drained accordingly in the DEM. Quality check will be done for verification of ground elevation values with DEM elevation values by appropriately importing spot elevations in to the DEM and RMSE report will be prepared to check for the final accuracy.