Topographical Surveys

Topographical surveying involves accurately representing the natural and built world in a digital environment. Digital Surface Models (DSMs) represent and map the Earth’s surface and everything on it. Digital Terrain Models (DTMs) map the bare ground surface (terrain). These models can be created by interpolation of a Triangulated Irregular Network (TIN) or a raster gridded DEM depending on the application.

Contour lines are generated to indicate levels across the site. A points.csv file can also be used for this purpose. A terrain model created from photogrammetry can be improved by removing obstructions from the point cloud e.g. trees, construction rubble and in the case of the latter example, elevation values interpolated around the perimeter of the obstruction.

Generated contour lines (quarry)
DSM representing the terrain and vegetation on it; DTM representing terrain only. Datasets processed from aerial LiDAR data from OpenTopography

We are primarily using photogrammetry-based methods for topographical surveying. Limitations exist when using this tool-set in terms of vegetation. For example, if it’s a grassy area, the longer the grass, the less accuracy that can be expected. Future investment in airborne LiDAR technology will solve this problem due to the ability of laser pulses to penetrate vegetation to the ground level.

Orthomosaics are a photogrammetrically orthorectified image mosaics where geometric and lens distortion has been corrected for. These products can form the basis of additional products that we can provide: as-built documentation and CAD drawings.