DSM, DEM, and DTM are all different ways of visualizing three dimensional relief of the landscape. All begin with overlapping aerial photos which can be viewed in stereo as 3D images by our photogrammetrists. A regular grid of points, called spot heights, is superimposed on the images where elevations are measured and recorded. The spot elevations can then be interpolated to form a surface which can be used to overlay a wide variety of GIS and CAD data.
A digital surface model (DSM) is a topographic elevation model of the Earth’s surface including every natural and artificial feature. DSM forms the basis for creating true orthophoto production.
A digital elevation model (DEM) is similar, but includes only bare earth features without vegetation or structures.The DEM data is used to create a terrain surface, terrain orthorectification and to generate contour lines.
A digital terrain model (DTM) takes the DEM a step further, and uses break lines in addition to spot heights to refine the model. The breaks are identified from our orthophoto and delineated along terrain impacting features such as ridges, valleys, watercourses, road edges and structures. When the spot heights are interpolated to create the terrain model or contour lines, the terrain disruptions at the break lines are taken into account to produce a more true to life representation of the surface.
First Base Solutions has an inventory of DTM as spot heights and break lines from our 2002 orthophoto that has been divided into tiles and is provided in DWG format with 3D polylines. The capture of the topographic model of the surface includes elevations on a 40 m to 50 m grid spacing with an accuracy of +/- 40 cm. Break lines were added along visible terrain impacting features such as the edge of roads, drainage and center line of railways. These elevation models are available through MapWarehouse covering the greater Toronto area and Simcoe Kawartha Regions. Contour lines at 1 m intervals are available for the same coverage in DGN format for MicroStation. Custom elevation models can be created for your project based on newer or custom acquired photo at intervals up to 1/2m.