Why Do PC-DMIS and Geomagic Control X Give Different Positional GD&T Results?

Hey everyone,

I recently ran a positional GD&T callout in PC-DMIS, referencing three datums, and then ran the same callout in Geomagic Control X using the same data and the same three datums. The issue? I got different answers.

Shouldn’t they be the same? Both software packages are supposed to follow the same GD&T standards (ASME Y14.5 or ISO), and I’m using the exact same dataset for both.

I understand that different metrology software might have variations in how they interpret and compute positional tolerance, but I’d like to get a better grasp on why this happens.

Some possible reasons I’ve considered:

• Datum Feature Extraction & Registration – Maybe the way each software establishes the datum reference frame is slightly different?
• Tolerance Zone Calculation – Could there be differences in the math behind positional tolerance evaluation?
• Software Interpretation of Standards – Are there minor differences in how PC-DMIS vs. Geomagic applies ASME Y14.5?
• Data Processing & Filtering – Does one software handle measurement data differently (e.g., filtering, outlier removal, fitting methods)?

Has anyone else experienced this? Do you know if Hexagon (PC-DMIS) and 3D Systems (Geomagic Control X) handle positional GD&T differently in a way that would explain the discrepancy?

Would love to hear your insights! Thanks in advance.