Tip 42: Multiple scales in photogrammetry

Posted on Tuesday, July 23rd, 2013

Tip 42 ScreenA photogrammetry project typically needs an external scale. With photogrammetric measurement and modeling, the scale is not known until specified. For example, the photogrammetry program does not know if you are inputing photos of a small toy car, or of a full size car. 

The two cases where one does not define a scale are:

  1. the project is done with other external constraints such as xyz control points, or
  2. only relative measurements or model shape are needed.

An external scale is defined by choosing two solved 3D points in the project and telling the program what the known distance is between them.

Two scale examplePhotoModeler provides the capability for inputing a number of different types of external data and constraints. The most common is a scale. PhotoModeler can handle one or more scales. Multiple scales help spread out the error and are great for cross-checking and verification (with one scale there is no redundancy).

This tip video demonstrates how to use the External Geometry Explorer (EGE) in PhotoModeler to set up and review multiple scales.

Watch the tip video below (or on Youtube).


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