RPS ALIGNMENT WITH OF A POINT CLOUD WITH CAD ELEMENTS

[metalurgicaprogreso]

Dear All,

I have a situation I would like to discuss. In our company we have a 3d scanner and use it to measure parts.

When I import the point cloud to PowerInspect I have to create the geometric entities for my RPS alignment in the point cloud. This forces me to create these entities for each measurement.

I would like to create these entities in the cad model, so that I can exchange the point clouds and all settings would stay there. In other words, it should work as a "template".

I hope I'm making myself clear enough.

Thanks in advance for the help.

[Philip_Hewitt]

Hi @metalurgicaprogreso 

You can use the Geometry Explorer / Wireframe checker functionality to define geometric features that you want to measure.  To define geometric features that will be evaluated from your point cloud, select 'Point-Cloud-Feature- Extracted from Clouds' (for example 'Point-Cloud-Circle- Extracted from Clouds').  I've attached a short video where I created three circles.  If you examine the geometric features created, you will see that the 'Point Sources' tab is set to evaluate data from 'All point-clouds.'  

As soon as point cloud data is available *in the region around the geometric feature*, PowerInspect will try to evaluate the geometric feature from the points in the scan data. 

This (the fact that the point cloud scan data must be positioned by the feature) means that this method is not suitable for the initial alignment of unaligned scan data.  If the scan data is not aligned, you will have to create the initial alignment with a different alignment method such as 'best fit from point cloud.' 

The results will cascade though- the initial alignment can be updated by subsequent features and alignments.

I hope this is helpful.  If you're having problems with a particular step in the process please give more details.

[metalurgicaprogreso]

Thanks dor the response. I tried what you suggested, and managed to create a couple of circles. I had to lower the "Search Distance" parameter to 0.1 mm, because it would not work otherwise. Is this ok? I could not find any help content regarding this parameter.

There is one more step I need to make. I'm trying to make an RPS alignment. I have the two circles, but now I need 3 points. I normally use dynamic points, but with a point cloud I do not know how to use them.

Thanks in advance for the patience and help :).

[Philip_Hewitt · Accepted solution]

@metalurgicaprogreso 

It is possible- just about.  It's not obvious or easy, and it's a rarely used feature which isn't really documented.   I'm not surprised you do not know this!

You need to create Geometric 'Point Cloud Single Point' elements.  It's possible to create these from a laser scan point source as before.

The bit that's not obvious is how to create these from dynamic points.  If you have some dynamic points, you have to select and copy each one individually.  When you have selected a dynamic point, you can paste the values to define the nominal position of the Point Cloud Single Point.  You do have to create the surface vector yourself.

It's not obvious or especially convenient, but it's not a big problem in the common cases where the surface vectors are aligned with CAD axes like X+ or Z+.

It's more difficult if you have a more complicated angled surface.  In that case you have to select the dynamic point, copy all the values to an editor (like Notepad), and then copy and paste the I J K vectors individually as Cartesian coordinates.

I've attached a video that shows and tries to explain this.  I hope it helps.

"I had to lower the "Search Distance" parameter to 0.1 mm, because it would not work otherwise. Is this ok? I could not find any help content regarding this parameter."

The search distance is how far it looks beyond the nominal values for the feature (position and size) to include points for the point cloud.  0.1mm seems low unless the parts are very accurate and the alignment is very repeatable.  Are there other features or edges (breaks in the point cloud) nearby?  It's probably detecting sharp edges which are dominating the feature evaluation.  It may be worth copying and trimming the point cloud to remove edges or features.

[metalurgicaprogreso]

I'm sorry I did not follow this up. Your information was very helpful.

Thank you very much for the help!!! @Philip_Hewitt