Orthophoto
An orthophoto is an aerial photograph or image geometrically corrected "orthorectified" such that the scale is uniform: the photo has the same lack of distortion as a map. Unlike an uncorrected aerial photograph, an orthophotograph can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for topographic relief lens distortion, and camera tilt.
Orthophotographs are commonly used in Geographic Information Systems (GIS) as a "map accurate" background image. An orthorectified image differs from "rubber sheeted" rectifications as the latter may accurately locate a number of points on each image but "stretch" the area between so scale may not be uniform across the image. A digital elevation model (DEM) is required to create an accurate orthophoto as distortions in the image due to the varying distance between the camera/sensor and different points on the ground need to be corrected. An orthoimage and a "rubber sheeted" image can both be said to have been "georeferenced" however the overall accuracy of the rectification varies. Many GIS software can display the orthophoto and allow an operator to digitize or place linework, text annotations or geographic symbols (such as hospitals, schools, and fire stations). Some software can process the orthophoto and produce the linework automatically.
Satellite Orthophoto
Satellite imagery and aerial photographs play an important role in general mapping, as well as GIS data acquisition and visualization. First, they help provide a solid visual effect. Many people are more able to put spatial concepts into perspective when they see photos. In addition, the secondary and perhaps more vital role is to provide a basis for gathering spatial information.
Examples of this are features such as roads, vegetation and water. Before this information can be gathered in a manner that is useful for a mapping or GIS system, the image data must be prepared in a way that removes distortion. This process is called orthorectification. Without this process, you wouldn't be able to make direct and accurate measurements of distances, angles, positions and areas.
Case Study
Uav Orphophoto
Aerial photogrammetry was once the sole purview of full-size manned aircraft with expensive aerial photogrammetric cameras. Now relatively inexpensive and intelligent UAVs that can carry consumer and presumer cameras have changed the access to aerial mapping systems, instead of limiting their use only to large budget projects. Examples of UAV photogrammetry are golf course mapping, large accident scene diagramming, mining documentation and stockpile volume measurement.
Advances in photogrammetry software have made using the images from UAV cameras much easier as well. There are a number of interesting outputs from UAV photogrammetry such as maps and diagrams, contour maps, DTMs, volume measurements, ortho-photos and photo-mosaics.
