Same pore size, different distance to the surface
Two cavities can have the same volume and very different positions within a part. This teaching example separates pore size from distance to the outer surface.
Input and calibration
A 40 × 40 × 40 voxel volume contains a solid cube at indices [8:32, 8:32, 8:32]. Its intensity is 1000; air is 0. Two 3 × 3 × 3 cavities occupy [14:17, 14:17, 10:13] and [18:21, 18:21, 15:18], in Z,Y,X order. Voxel spacing is 1 µm in every direction.
Method
Threshold the solid at 500 with the actual pores_core.analyse function, keeping the largest solid component and the default 26-connected background. Measure both surface-to-surface and voxel-centre-to-exterior-centre distances.
Computed results
| Cavity | Volume (µm³) | Surface distance (µm) | Centre distance (µm) |
|---|---|---|---|
| 1 | 27 | 2 | 3 |
| 2 | 27 | 7 | 8 |
Both pores occupy 27 voxels, hence 27 µm³ at this calibration. The surface distances are 2 and 7 µm; the corresponding centre distances are 3 and 8 µm. The one-voxel difference is expected for these parallel surfaces. Size alone does not express proximity to the surface.
What this demonstrates
The clean, axis-aligned geometry supplies an analytical check. Real scans add noise, segmentation uncertainty and oblique surfaces. These numbers do not establish accuracy on customer data or a mechanical acceptance threshold.
Reproduce the geometry
Construct the two-level volume from the array indices above, use the stated voxel spacing and threshold, and apply the same boundary setting in Pores to Surface Analysis. See the linked guide and manual for the application workflow.