Measuring in Cloudcompare

[agb123]

I am measuring two different types of shells in Cloudcompare. I used the point picking tool to get a distance. However, the numbers CloudCompare are giving me seem arbitrary. Shell 1 is clearly smaller in person than Shell 2, but the program basically gives me numbers too similar to be true. How would I actually get a legitimate measurement in Cloudcompare?

[daniel]

CloudCompare displays all measurements in the same units as the coordinates of the 3D entities. Units are not explicitly saved in most 3D files... therefore only the user can determine what the real units are.

Pay attention also that SfM/photogrammetric clouds or meshes have often an arbitrary scale unless you have use Ground Control points or other equivalent scaling mean during the data generation process.

[agb123]

Okay, I used Agisoft Photoscan to build the models, so they definitely have an arbitrary scale. I want to assign a scale in CloudCompare. My model is a shell on top of a grid with 1 cm squares to use to assign a scale. Is it possible to assign a scale by just dropping points onto the grid I already have? I don't want to import anything else.

[daniel]

Do you mean that you you see the grid in the cloud (and this part of the cloud is flat)?

If yes, then you can either use the picking tool measure the distance between intersections of this grid to deduce a rough scaling (that you'll be able to apply with 'Edit > Multiply / scale').

Or you can even use the 'Align' tool (see http://www.cloudcompare.org/doc/wiki/in ... itle=Align) and pick several intersections for which you can assign arbitrary coordinates (e.g. (0, 0, 0), (1, 1, 0), etc.) to scale the cloud in a more robust way. Make sure the 'adjust scale' option is checked of course.

And I bet Photoscan has also some integrated solution for this?