CloudCompare forum

Hello,

I've been using the roughness tool lately and had assumed that the 'distance' to the least squares best fitting plane from the point in question is a vertical distance.
However, a colleague of mine has questioned this and suggests it may be the shortest distance to the best fitting plane. Please can you clarify which distance is used by the roughness tool?

Many thanks, Amy

Indeed it's the shortest distance to the plane. We have no reason to prefer the Z direction in the general (3D) case.

Thanks for the quick reply Daniel.

Would there be a possibility to introduce an option to the roughness tool, where the user can select shortest distance or vertical distance? For those of us working on relatively flat landscape scenes, using the vertical distance may be more meaningful. It'd certainly be interesting to test this out at least.

Many thanks, Amy

Hum, in this case do you also intend to compute a purely vertical 'best fitting plane'? Because otherwise I'm not sure what you would measure...

Hi Daniel,

I have some questions regarding roughness calculation by PoinCloud and I would be grateful if you could answere my questions:
1. There are different parameters for roughness such as Arithmetic average height (Ra), Root mean square roughness (Rq) and so on. I was wondering what kind of parameter is calculated by PointCloud software as a roughness.
2. What is the unit of the value of roughness generated by this software.
3. I had one original surface and then added some small dents on the surface, Is there any possibility to use pointcloud software for calculating the roughness of new surface wit respect to original one. In other words, is it possible to calculate the roughness by having the new and reference point clouds?
Thank you very much for your time and consideration in advance.

1. See the 'notes' here: http://www.cloudcompare.org/doc/wiki/in ... =Roughness. We use a very simple algorithm.

2. Therefore the units are the same units as the cloud (depends on your file)

3. It's a bit tricky but it might work: you can use the 'Tools > Volume > Compute 2.5D Volume' calculation tool to compute the difference between the two surfaces (just make sure they are oriented roughly in the XY plane first).

You then have an option (with the latest 2.9 beta version) to export the 'difference' scalar field.

Next you can convert these differences (scalar field) to the Z coordinate (with 'Edit > SF > Export to coordinates'). This way you can kind of unwrap one surface relatively to the other.

And eventually you can compute the roughness of this new surface.