Aerial photography in its simplest form is full of distortions. The two largest distortions are known as “Key Stone” and “Relief Displacement”. The Key Stone effect can be removed by “rectifying” or registering a photograph to a few known points. Relief Displacement must be corrected by reference to a digital terrain model (DTM).
The ortho image to the right shows an aerial photograph that has been geometrically controlled with airborne global positioning system (GPS) measurements and ground based survey control points. ALS, Inc.’s staff photogrammetrist has performed autotriangulation to tie all three elements together and produce a DTM. Ortho images of this type allow the user to take accurate measurements from the image and can serve as a base or control layer for graphical information systems (GIS).
ALS, Inc. provides custom orthometric correction of aerial photography to produce ortho images. These images have rectangular map features which are useful at engineering detail level. After 31 years of doing business in Texas, ALS, Inc. has in stock a complete library of ortho images of Harris County, Texas as well as all adjoining counties.