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What is Photogrammetry?

Photogrammetry is the science of using photos to make measurements and maps. By taking overlapping aerial images from planes or drones and viewing them in 3D, we can measure distances, create accurate maps, and build models of the world.

In transportation and GIS, photogrammetry helps us understand what’s on the ground, and how the land is shaped, so engineers can design safe, reliable infrastructure.

What is Plan and DTM?

Before any Planimetric mapping begins, we first collect aerial data using drones or airplanes equipped with high resolution specialized cameras and LiDAR sensors. 

This imagery and LiDAR data are then processed through the Aerial Triangulation (AT) workflow, where we “tie” the overlapping images together and align them using ground control points and flight data. This step ensures all photos are accurately positioned in 3D space. Once the AT meets required accuracy standards, the imagery is ready for precise planimetric/topographic feature extraction.

As a Photogrammetric Technician, I focus on two primary mapping products:

Planimetric (PLAN) – 2D feature layers such as road edges, sidewalks, buildings, utilities, hydrology, and vegetation. These are extracted through 3D photogrammetry and become GIS-ready layers used for asset mapping, planning, and basemap updates.

Digital Terrain Models (DTM) – A detailed representation of the ground surface built from breaklines, spot elevations, and void areas. DTMs support roadway design, drainage analysis, 3D visualization, and GIS elevation products like contours and hillshades.