The Transform between length in 3D model and the truth

[pro.young]

Hi, everybody.
I am trying to calculate the roughness of the soil using the 3D model by PhotoScan Standard. So I want to know the correspondence between the length in 3D model and the truth length on the ground.
Here I have some questions:
(1) In Photoscan Standard, if there are no control points, what is the unit of the length in the 3D model built by Agisoft Photoscan Standard version? or how to respond the length in the model to the truth?
(2) If I use Photoscan Pro, is it possible to scale a model with only known distances between control points? Also, is it possible to create a cross-section of the model?

(I am a new man in this software, it's highly appreciate for your answers, thank you~)

[RHenriques]

Yes, you can scale the model using known distances or use markers with real world coordinates (Ground Control Points) in PS Pro. To do profiles or cross sections, you can export the DEM and use it in any Geographical Information System package to do so. Some are free. See qgis.org, for instance, install the application and download a plug-in called "profile tool". 

[pro.young]

I am trying this method, thank you very much!

[David Cockey]

Geometry created in the standard edition of PhotoScan has arbitrary units and the scale will be different in each project. The scale of the PhotoScan geometry can be determined if the actual distance between two points of the geometry is known. Measure the distance between those two points in PhotoScan, and the scale will be the ratio of the distance in PhotoScan to the actual distance. This scale will work for all distances in that particular geometry.

[pro.young]

Thank you for your advice.