Preparing the raster map
The first step consists of acquiring a good quality scan of the paper map or using an already available raster image.
It is important that the map is readable, not distorted and preferably includes a kilometer grid or visible geographic coordinates.
Selecting calibration points
Control points must be easily identifiable on the map and have known coordinates.
Grid intersections, geodetic markers, road intersections or other precise cartographic references are generally used.
Assigning coordinates
After selecting the calibration points, it is necessary to enter the correct coordinates according to the map coordinate system.
The software will automatically calculate the geometric transformation required to align the image with real-world coordinates.
Checking calibration accuracy
Once georeferencing has been completed, it is important to check the map accuracy by comparing known points or real GPS data.
Any errors may depend on imprecise control points, an incorrect datum or distortions in the original scan.
Using georeferenced raster maps
Calibrated maps can be used to display GPX tracks, waypoints and outdoor routes with geographic accuracy.
This allows historical cartography, scanned hiking maps and custom images to be integrated into GPS software.
Georeferencing maps with OkMap
OkMap includes dedicated tools for raster map calibration and coordinate system management.
The software makes it easy to associate control points, check calibration errors and immediately use georeferenced maps with GPS tracks and data.