Detect identical points shared by two different clouds

[carlisle_h]

I'm looking for a way to compare two separate point clouds in order to determine if any points are common to both. I have two files, let's say a large and a small one, and I suspect the small one is simply a subset of the larger one, but I'd like to see if that is true for the entire dataset. I have found a few ways to identify duplicate points within a single cloud, but not comparing two. At first I thought I could just merge the large and small together, and then identify duplicate points, but that does not tell me which ones were common to both.

thanks,
Carlisle

[daniel]

You can simple compute the C2C distances between the two clouds (use the small one as the 'compared' cloud).

Then you'll see if all points have a 0 distance (or almost zero). And you can even segment the cloud based on the distances to know how many points have exactly a zero distance.

[carlisle_h]

Thanks Daniel, that is very useful. I had not used the min/max tool before, very cool.

One follow up question that this brings up. It seems I don't have any distances that are actually zero, but there are thousands which are very small values, like 0.00030033. At what threshold should I consider these values to effectively be zero?

[daniel]

It mostly depends on the file/source of the data. For instance If it comes from an ASCII file with a few digits (or very big coordinates) then you may be already at the numerical accuracy limit.

As a rule of thumb you can consider that the smallest value that can be properly represented in memory is about the biggest coordinate in your cloud divided by 10^7.

[lna2020]

I have (x,y,z) ,and I want to fine where is this point in CC.
Can I key in the coordinate to find the point？
What should I do？Thanks.

[daniel]

The best way to localize a point is to create a sphere (with the Primitive Factory) and then translate this sphere with 'Edit > Apply transformation' (use the second tab, and simply set the points coordinates as 'translation').

You'll have to set a small radius for the sphere if you want to properly localize the point (you can change it afterwards in the sphere properties).