 # When measuring 3D objects, 3D ROI Manager outputs SurfCorr(pix), what is this parameter?

The Measure 3D function in the 3D ROI manager outputs a number of parameters. One parameter that is outputted is SurfCorr(pix).

Can someone explain the significance of this parameter or how it is calculated. I am thinking the CompCorr(pix) and SpherCorr(pix) are calculated using this value for surface area, but want to be sure.

my voxel dimensions are 0.1415 x 0.1415 x 0.9994µm

Also if someone can give an intuitive explanation for the difference between sphericity and compactness (other than one is the cube root of the other) that would be really helpful.

Cheers!

Ian

Hi @Whelan_Ian,

There are many ways to compute 2D surface for a 3D binary object, the method used for SurfCorr is based on the paper Surface area estimation of digitized 3D objects using weighted local configurations (link), that will smooth a bit the raw surface computed from voxels faces.
Yes, the two other parameters CompCorr and SpherCorr are computed using the value of SurfCorr.
Finally, there is no difference between sphericity and compactness except one is cube root of the other, I guess some people are used to use one or the other.

Hope this helps,

Best,

Thomas

Thomas,

This was great, thanks for the reference!

Is there a mathematical rational for cubing sphericity to get compactness?

Cheers

Ian

Hi @Whelan_Ian,

Since the Compactness is the ratio between the square of the volume to the cube of the surface (with some coefficient to make it 1.0 for a sphere). I guess having the surface (not its cube) in the ratio may makes more sense, eventually.

Hi,

I have the same issue trying to understand how the surface area is calculated in the 3D ROI manager and how the conversion is calculated from pixels to unit (e.g. microns).
For instance for the volume conversion you just multiple the volume in pixels x the calibrated volume of a voxel. But how do you convert the surface area?

And what is the difference between Surf and SurfCorr? Which one is more accurate?

Thanks!

Talia