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What Is aerotriangulation?

Aerotriangulation and/or Ground Control Aerotriangulation is the process of assigning ground control values to points on a block of photographs by determining the relationship between the photographs and known ground control points.

The overlapping portions of adjacent photos are registered to one another using "pass points" on the photos. Pass points are marks (usually small holes made in the emulsion) that are strategically placed so that they are visible on each of three adjacent photographs within a strip. This method is more commonly referred as "pugging", which refers to the action of drilling a small hole in the emulsion of the film positive using a point transfer device equipped with a diamond tip drill with a diameter of 60 microns. The overlapping region of two or more photos in the strip is referred to as a "model."

An advantage of the aerotriangulation process is that it reduces the need for field-surveyed ground control. The traditional method of establishing control points is through the use of field surveys whereby surveyors measure the control point data. This method, however, can be quite costly, especially for large map production projects, and may be impossible in some instances due to difficulties in accessing the property. The aerotriangulation process can reduce the need for field-surveyed control points because much of the orientation information can be determined mathematically based on the sharing of control point information across adjacent models.

Reference: Vision International, A division of Autometric, Inc, OrthoKork Centre for Topographic Information (Ottawa), Geomatics Canada

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