GIS - Digital Elevation Models

A DEM (Digital Elevation Model) is a collection of discrete elevation points at regularly spaced intervals, while a DTM (Digital Terrain Model) defines topographic shapes by elevation points at significant topographic features which reflect abrupt changes in relief such as incised streams, ridge lines, and slope breaks.

In either case, these data points provide a regular (DEM) or irregular (DTM) pattern of elevation information that can be used for many purposes, such as the generation of a triangular irregular network (TIN), where groupings of three elevation points create adjoining triangular surfaces which mathematically approximate the ground surface.

Orthorectification

An orthophoto map is produced by removing scale variations from the original aerial photography. The original aerial photograph is not a true map because as the elevation of the ground changes, the scale of the image also changes. By using an accurate representation of ground elevations, we are able to fully rectify the ortho image so that all features are correctly located.

We do orthorectification of aerial photographs & spatial imagery to produce map-quality ortho images. In preparation for orthorectification of air photos or satellite imagery, we obtain the source material to extract digital elevation models. Masspoints, breaklines, and contour interpolation features (CIP) are collected and processed in specialized software to generate digital terrain models. Cross sections of corridors are generated from 3D data for the design of highways, pipelines, and powerline rights-of-way.

Our Remote Sensing & Digital Photogrammetry Practice is powered with full feature PCI, Intergraph, ERDAS & ER Mapper workstations with dual monitors.