Tip 35: Setting the Dominant Coordinate Axis in PhotoModeler

Posted on Monday, April 15th, 2013

Tip 35 VideoWithout any external input, photogrammetry projects don’t know which way is ‘up’.  For example, if you’ve modeled a hard-cover book with photogrammetry, it doesn’t know if the book is lying on a table where the cover would be considered ‘up’, or if it’s on a bookshelf where the cover is facing to the side.

This is a similar issue to how scale is unknown until defined by external information; as described at the bottom of the How it Works page. Another blog post that talked about coordinate systems is Tip 22.

To set up a precise orientation one defines two of the X, Y or Z axes. You pick two 3D points or a 3D line in the project and tell PhotoModeler, “this line is the X axis”, or similar.

PhotoModeler Screen Shot

One interesting question of this axes definition process is: “What happens if the lines used to define the axes in the project are not perpendicular?”  If you want to define the X and Y axes (which mathematically are perpendicular), what happens if the X line is not perpendicular to the Y line? Which does PhotoModeler choose as being correct?

This is controlled by the Dominant Axis feature.

Watch the video to see how to pick the dominant axis and see what it means. On Youtube you can also watch at a larger size and in high def.


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