topic Re: Intelligent Decimation? in ReCap Forum

Intelligent Decimation?

Pointdump — Thu, 22 May 2025 16:53:20 GMT

"Intelligent decimation provides a method to extract key points from a source classification and move them to a target classification."

So all the points that are "decimated" are "moved"? They are no longer Ground (2) points? I'm struggling to understand why this would be useful.
Dave

Re: Intelligent Decimation?

zhaoyang_ma — Fri, 23 May 2025 07:44:03 GMT

Hi Dave,

You need to specify a target classification which is different from the source classification.

Best regards!

Re: Intelligent Decimation?

Pointdump — Fri, 23 May 2025 05:33:18 GMT

Hi Zhaoyang,
Thank you. I understand that from the Help. My question is why anyone would want to do that.
Dave

Re: Intelligent Decimation?

zhaoyang_ma — Fri, 23 May 2025 08:00:23 GMT

Hi Dave,

To explain the case in a clearer and simpler way, let's assume we have a project without regions or hidden scans.

In this project, there is only one classification "2 Ground" which contains 1 million points. Now you can use intelligent decimation to move ~1% of points in the "2 Ground" classification to the "8 Model key-point (mass point)" classification.

Then you can hide the "2 Ground" classification. Now there are only around 1000000 * 1% = 10000 points visible at most.

You can then export the project to a unified project. The resultant project contains less than ~10000 points. Comparing with the original project, the new exported project is light-weight. The light-weight version of project is faster to be used in further down-streaming operations. For scenarios when there are no requirements to accuracy or geometry fidelity of the point cloud, the light-weight version of project can be used to save time.

Best regards!

Re: Intelligent Decimation?

Pointdump — Fri, 23 May 2025 10:29:21 GMT

Zhaoyang,
Thank you. I understand all that, and I clearly see a need to decimate points before using them in Civil 3D. Keeps the total number of surface points to less than 2 million to avoid the dreaded kiss-of-death MMS file. I normally thin points in CloudCompare, but I wanted to investigate thinning points in ReCap.
However, Intelligent Decimation is not intelligent. It is klunky and un-intuitive. I have no reason to save points as "8 Model key-point (mass point)". I should be able to just save a thinned cloud as Ground(2).
"...export the project to a unified project."
What is the distinction between a project and a unified project? What makes a project "unified"?
Dave

Re: Intelligent Decimation?

Pointdump — Mon, 26 May 2025 19:58:27 GMT

Zhaoyang,
Decimate Points works very well to thin points to a manageable level to create a surface in Civil 3D. Works much better than the entirely inadequate upfront Decimation Grid maxed out to 100mm.
BUT...
It could stand a little improving. I'll probably post this in ReCap Ideas.
1. Decimate literally means "remove one in ten". Thin Points would be a better name.
2. Once you decimate Ground(2)points to the insanely named "8 Model key-point (mass point)" classification, all the other classifications disappear, even though hovering the cursor over Scan Locations still shows the original large amount of points. I started with Ground(2) points, and that's what I'd like my points to remain.
Dave

Re: Intelligent Decimation?

zhaoyang_ma — Tue, 27 May 2025 04:54:46 GMT

Hi Dave,

The second case you mentioned is unexpected. Do the other classifications come back if the "Refresh classification list from point cloud data" button is clicked?

Best regards!

Re: Intelligent Decimation?

Pointdump — Tue, 27 May 2025 06:26:03 GMT

Zhaoyang,
No, "Refresh classification list from point cloud data" does not bring them back. I'm probably missing some crucial step.
My point cloud, attached, has:
histogram of classification of points:
909527 unclassified (1)
2144872 ground (2)
3228 noise (7)
Total: 3,057,627 Pts
Here's my workflow:
1. Create ReCap Project with point cloud
2. Decimate by approximately 10,000 points
3. Delete all classifications except "8 Model key-point (mass point)"
4. Exit and Save/Optimize
5. Re-Open project. 3+ million points still there, only "8 Model key-point (mass point)" classification remains.
6. Importing RCP into Civil 3D shows 3,048,831 points.
Dave

Re: Intelligent Decimation?

zhaoyang_ma — Wed, 28 May 2025 01:52:36 GMT

Hi Dave,

Thank you so much!

In the above steps, could you change step 4 from "Exit and Save/Optimize" to:

Create a new folder and save the current project as a new project in a new folder by using the "Save As" button (A new folder is just to ensure the new project does not overwrite any existing files)

In the pop-up "remove deleted points" dialog, choose "remove 3D point cloud only"

For step 5, you can open the new project and check.

For step 6, you can also use the new project.

But if you want to bring back the classification list in the project mentioned by you, you can recover the deleted points by clicking the button as illustrated:

NOTE: when checking/learning features involving deleting things (e.g., points, classifications), please create backup projects to avoid data loss.

Best regards!

Re: Intelligent Decimation?

Pointdump — Thu, 29 May 2025 15:57:57 GMT

Zhaoyang,
Thank you for those Key Distinctions!
I'll keep this thread bookmarked.
Dave

Re: Intelligent Decimation?

zhaoyang_ma — Thu, 29 May 2025 05:37:22 GMT

Hi Dave,

Thanks again!

While the suggested "Save As and Remove Deleted Points" workflow works for you, the export workflow could work better in many cases. For my previous answer, for the usage scenario, it is better to say that it is to use the "Save As and Remove Deleted Points" workflow instead of the "Save and Optimize Project" workflow which you have tried earlier.

Best regards!