georeferentsi

Georeferentsi (georeferencing) is the process of assigning real-world geographic coordinates to the geometry of a dataset, so that it can be integrated with other spatial information. It is commonly applied to raster data such as scanned maps, aerial photographs, or historical imagery to align them with a known coordinate reference system and with vector layers.

Georeferencing relies on ground control points (GCPs), points on the image whose true coordinates are known from an existing reference layer. A transformation model is then selected to map image coordinates to geographic coordinates. Common models include affine (six parameters), projective, and higher-order polynomial transformations; the chosen model reflects the distortion in the source and the required accuracy. The process yields a georeferenced raster and metadata describing the coordinate system, transformation parameters, and an error metric such as RMSE (root-mean-square error).

Output and accuracy considerations are important. The georeferenced image is assigned a coordinate reference system (CRS) and can be resampled during processing. Accuracy depends on the quality and spatial distribution of control points, image resolution, terrain distortion, and the transformation model. Users must balance computational complexity with the desired precision. Acceptable residual errors should be monitored to ensure useful alignment with other spatial data.

Applications of georeferencing include restoration and integration of historical maps, urban planning, environmental monitoring, and cartographic production. Software tools commonly used for georeferencing encompass QGIS Georeferencer, ArcGIS Georeferencing, GRASS GIS, ERDAS Imagine, and similar GIS suites.