orthorektifointi

Orthorektifointi is a Finnish term that translates to "orthorectification" in English. It refers to the process of correcting geometric distortions in a digital image, particularly aerial or satellite imagery, to create a planimetrically accurate representation of the Earth's surface. This process involves removing distortions caused by factors such as the sensor's viewing angle, the Earth's curvature, terrain relief, and lens aberrations.

The core of orthorectification is the application of a digital elevation model (DEM). The DEM provides information about the elevation of the terrain, allowing software to adjust the image pixels to their true ground positions. By resampling the original image data based on the DEM and geometric sensor information, an orthophoto is produced. An orthophoto is a geometrically corrected aerial or satellite image where displacement caused by terrain and tilt have been removed.

The output of orthorektifointi is an orthophoto or orthophotograph, which has a uniform scale throughout and can be used for precise measurements, mapping, and analysis. Unlike a simple aerial photograph, an orthophoto can be directly used in Geographic Information Systems (GIS) and other spatial applications without further geometric correction. This accuracy makes orthorectified imagery invaluable for tasks such as land use planning, environmental monitoring, urban development, and disaster response. The process requires accurate sensor orientation data and a high-quality DEM to achieve the desired level of geometric precision.