M3C2 Plugin - change detection

[sbracey]

Hi,
Im wondering if I am understanding this correctly. I am looking to determine what change has occurred between two datasets. I aligned them and registered so that they matched, then used the M3C2 plugin to show the distance between points on each dataset. The screenshot shows red, green and blue dots with the scale. Am I correct in thinking the red dots show positive change (i.e an increase in elevation around the item), the green show no change and the blue show a negative change?

Also can anybody help me to understand the scale of change? For example is 0.019415 in mm, cm etc?

Screenshot attached

Thanks in advance!

[daniel]

Yes, according to the color scale, red corresponds to positive distances and blue to negative ones. And you should hopefully be able to compare this visually by looking at the 2 clouds more closely.

Else, CloudCompare doesn't know the units in which the coordinates of your points are expressed in. This is not included in most of the file formats. Therefore it simply loads the coordinates as is and display distances and other metrics in the same implicit units.

[sbracey]

Thanks very much

I’m still not sure what the scale is trying to show. I understand that we have the positive and negative change but not sure what the units are. Is there a way of finding this out?

[daniel]

The only way is to guess the units based on the scale of the things you are looking at (and the scale bar at the bottom right of the screen, or you can measure the distance between 2 known points, etc.).