What is the difference between an orthophoto and an ordinary aerial photograph

The film diapositives are later scanned with a precision image scanner to create a raster image file.

Digital Terrain Model The digital terrain model DTM can either come from an existing source or it can be developed from the aerial photography. The aerial photos are taken using a stereoscopic camera, with which two pictures of a particular area are simultaneously taken, but from slightly different angles. The overlapping area of the two resulting photos is called a stereo pair. Using a computer called a stereoplotter, the stereo pair can be viewed as a single image with the appearance of depth or relief.

Ground control points are established based on ground surveys or aerial triangulation and are viewed in the stereoplotter in conjunction with the stereo pair. In this setting, the image coordinates of any x,y,z point in the stereo pair can be determined and randomly selected and digitized. These points, in conjunction with the control points, comprise the data points for the DTM.

The accuracy of the final digital orthophoto will depend in large part on the point density of the DTM. Like other maps, the end user can measure directly from the orthophoto without having to correct for distortion.

Unlike an aerial photo, a cartographer can overlay additional information on an orthophoto map. She can use the orthophoto as a source or background image in a geographic information system GIS or use it to review, revise or to collect more information on another map. Whereas an orthophoto gets used as either a map or in combination with GIS, an aerial photo gets used more when the photographer wants to show a different perspective of the Earth.

Many building owners or real estate agents use aerial photography to show their clients an unusual view of the property. Aerial photos therefore do not feature a unified scale; the height difference in the position of the object on the landscape causes the size of the object on the aerial photo to seemingly change.

Aerial photos therefore cannot be used for planimetric measurements as all essential geometric elements such as distances, angles and surfaces are distorted. It is evident that roads and facilities are tilted. Through an orthophoto procedure, the aerial photo can be converted from central to orthogonal projection, thus largely eliminating the above-referenced weaknesses of central projection. An orthophoto is therefore an aerial photo converted into orthogonal projection by taking into account data on the relief and the absolute orientation of aerial photos.

The terrain area on an orthophoto is displayed in a unified scale. But what is an orthomosaic? How are they being used? And why would you want one? Like this video?

Consider subscribing to our YouTube channel for more like it. Put simply, an orthomosaic is like Google Earth, but way sharper. It is a large, map-quality image with high detail and resolution made by combining many smaller images called orthophotos. These corrected orthophotos have no distortion whatsoever and a uniform scale across the image.

The key difference between a normal aerial photo and an orthophoto is the perspective and accuracy.