Orthophotography

An Orthophoto is an aerial photograph geometrically corrected (orthorectified) such that the scale is uniform, and distortion free. Unlike an uncorrected aerial photograph, an orthophoto can be used to measure true distances, having been adjusted for topographic relief, camera position, altitude, camera lens distortion and image scale variations. Viewed simply as an image or as background to a vector based map the orthophoto allows the user to actually view features on the landscape and better interpret those features.

Orthophoto are created by importing raster image files or scanning aerial photographs and converting them to a raster image file format. Control points are identified on the aerial photos, stereo models developed and geometric distortions are estimated. A digital terrain is either imported or collected and used to provide changes in elevation. Differential rectification applies the correction to the photography based on small equal sized pixels. The digital photograph is registered when each pixel is placed in its precise geographic position. Final digital orthophotography is then delivered in any tile scheme, required by the client, to match existing mapping, or to serve as a base for digital plan/topo, cadastral, utility or any mapping layer. Data can be delivered in compressed and / or compressed image tile formats on media of the clients choice.