compare two point clouds

[lparisi]

How can I extract the values of all height differences of two point clouds from CloudCompare? (the las files are from the same location but the data was collected at different times, so it's mostly a difference in the z-axis).

I would then like to import the elevation from the height differences into ArcGis PRO to visualize the elevation on a 3D map.

Does somebody have an idea?

[daniel]

The 2.5D Volume Calculation allows you to compute the height difference between 2 rasterized (gridded) versions of your clouds. You can then export the raster grid as a point cloud with the height difference as a scalar field.

[lparisi]

Thank you !

Howerver, I am still concerned about something...

I want to get the volume between two point clouds. The two point clouds are the same but one is just a couple of meters higher than the ground/before las file (there is only a difference in the Z axis). My goal is to understand the mechanism of calculating the volume of the space between two rasters.

I know the tool "compute 2.5D volume" can compare two las files but I am still trying to understand the whole process behind the tool.

Here are the steps I followed :

1. I rasterized the two las files using the parameters as shown bellow :
- In projection, I ticked "interpolate SF(s)" but I am not sure what it really means
- In Empty cells, I used "interpolate mode" which I think is more accurate than the other mode

2. Then I used the tool compute 2.5D volume thinking it can calculate the volume of the space between the two rasters :
- In red the volume of the space I want to calculate
- I used the interpolate mode for empty cells
- In the Grid, I used the average height in the cell height box (again thinking it's more accurate)

3. In the results :
- I have no removed volume (is this normal ?)
- The added volume is the same as volume
Here are the results :

Volume: 2,006,561.950
Surface: 1,002,001.000
----------------------
Added volume: (+)2,006,561.950
Removed volume: (-)0.000
----------------------
Matching cells: 100.0%
Non-matching cells:
ground = 0.0%
ceil = 0.0%
Average neighbors per cell: 8.0 / 8.0

Why is ground and ceil at 0% ?
Is 2,006,561.950 m3 the volume of the space between the two rasters that I want to calculate ?

[daniel]

1.
The first option has no impact on the positions of the points (it's just for the scalar values associated to the points)
And the other option (interpolate) is useful if there are holes in your cloud/raster.

2.
Looks good

3.
- Yes, if one cloud is above the other, then you'll have either only 'removed' or only 'added' volume (depending on the order in which the clouds are compared)
- The total volume = added + remove (so everything is logical)
- There are 0% of 'non matching cells' in both rasters, which is good (and quite logical regarding your workflow)

And yes, the total volume should be an estimate of the volume you are looking for. Considering that the surface is around 1e6 square units, I guess the vertical shift is around 2 units? It would makes sense considering the volume (~= delta_height * surface)