Modern spatial data acquisition and update workflows widely use orthophotos and three‑dimensional digital terrain models as source data. These products can be obtained quickly and efficiently and enable a wide range of tasks where the location of objects in space must be known.
Orthophotos
Despite the high visual clarity of modern aerial and satellite imagery, measurements on raw images are not sufficiently accurate until orthorectification is performed. Orthorectification is a digital transformation that compensates terrain relief and projective distortions introduced during imaging. The resulting orthophoto retains the visual properties of the source image and the metric properties of a map.
Orthophotos can be generated by processing satellite images, aerial photos, and images captured by UAVs (drones). Typical steps include flight with overlap (e.g., 60% along track and 30% across), ground control points, building a digital elevation model, orthorectification, and producing a mosaic orthophoto.
Effective applications of orthophotos include:
— cadastre and land management;
— map updating;
— municipal governance;
— territory monitoring;
— architecture and construction;
— geological works;
— master planning;
— base mapping for diverse applications.
3D digital models of territories
Many applications require a full three‑dimensional representation rather than a flat orthophoto. The most in‑demand are the Digital Surface Model (DSM) and the Digital Elevation Model (DEM). DEM models only the bare earth, while DSM includes 3D models of all objects on the surface (buildings, vegetation, etc.).
Modern geomatics allows DSM generation in several ways:
— photogrammetric processing of stereo imagery from aerial/space or terrestrial photography;
— airborne laser scanning with LiDAR;
— terrestrial laser scanning;
— processing of radar remote sensing data.
Various filtering methods are used to derive DEM from DSM. DEMs are commonly used to generate orthophotos, while DSMs are applied in municipal management, design and construction, radio planning, volume calculations, computer visualization, and more.