Terrain Modeling is the generation of a surface using a dense network of points collected during the analytical aerotriangulation and photogrammetric map data collection processes. Nearly 100% of all topographic projects are compiled using surface modeling techniques.

At Bradstreet Consultants, our team uses first order analytical stereoplotters, calibrated to within 0.001 millimeter, to take measurements, and Autometric's Softplotter NT softcopy photogrammetry system. In addition, we rely on software by Visual GIANT, Spectra-Precision and Kork Digital Mapping System, all are leaders in the mapping software and data capture industry.

Aerotriangulation may be utilized to generate a dense and systemmatic network of point data by computing X, Y and Z ground coordinates throughout a stereomodel or project area. Typically, the point data used to create DTMs is captured during the Fully Analytical Aerial Triangulation (FAAT) process.

From the topographic data collected during the photogrammetric mapping process, 3D coordinate data is extracted for the creation of a terrain model. All photogrammetric data captured in 3D is used. This includes the collection of hard and soft breakline features with supplemental random mass points to maintain mapping accuracies. Breaklines are a special class of lines used to form the surface where there are instantaneous slope changes in the terrain. Breaklines may represent drainage structures, road edges and center lines, retaining walls, ridge lines and escarpments. Since some of these items are collected as planimetric data, they can simultaneously be used as breaklines which eliminates duplication and the risk of errors.

Mass points are spot elevation data randomly collected in varying density to effectively and accurately define the surface. Masspoints and breaklines are used to create a Triangulated Irregular Network (TIN) surface. It is this surface which is the Digital Terrain Model (DTM), and used to create contours for your project area. Digital Terrain Modeling projects are processed through Spectra-Precision Terramodel software which has a direct interface with the photogrammetric KDMS data files. Terramodel has proven to be an extremely accurate and fast modeling package for all applications.

Terrain Modeling may also be represented as a gridded elevation data set that is oriented north up, Digital Elevation Models. Typically government agency data or smaller scales of map information (less than 1:25,000)are displayed in this manner. Visualization of DEM data can be in either raster form (shades of gray), relief shading, or log files. DEM data can be superimposed over stereo models for editing, accuracy verification, and visualization.