I found the equation to calculate the surface density is N/piR^2. What confused me is why it is not N/4*piR^2?
What does this "surface density" represent? Is it the density in part of a sphere?
The algorithm of surface density
Re: The algorithm of surface density
Why 4?
For each point, CloudCompare will extract the neighbors that fall inside a sphere of radius R. But then, you can assume your cloud is mostly (locally) flat, and choose to compute the surface as the number of points relative to the area of a disc (= pi.R^2). Or you can choose to compute the volume density, in which case the number of points will be divided by the volume of the sphere (= 4/3.pi.R^3).
For each point, CloudCompare will extract the neighbors that fall inside a sphere of radius R. But then, you can assume your cloud is mostly (locally) flat, and choose to compute the surface as the number of points relative to the area of a disc (= pi.R^2). Or you can choose to compute the volume density, in which case the number of points will be divided by the volume of the sphere (= 4/3.pi.R^3).
Daniel, CloudCompare admin
Re: The algorithm of surface density
Thank you for your reply.
So it is not the surface density of the sphere surface, but a cross-section of the sphere？
So it is not the surface density of the sphere surface, but a cross-section of the sphere？
Re: The algorithm of surface density
Ah, I see where the 4 comes from now ;)
No, it's indeed the cross section (at the equator) of the sphere, assuming the points are more or less on a plane locally (especially for airborne data for instance).
No, it's indeed the cross section (at the equator) of the sphere, assuming the points are more or less on a plane locally (especially for airborne data for instance).
Daniel, CloudCompare admin