#### Ignore CAD to Part

Old v3.0 Documentation: If you select the Ignore CAD to Part check box when saving an external alignment, then PC-DMIS only saves the machine to part alignment and does not save the CAD to Part. There's a relationship between the CAD coordinate system and PART coordinate system that has to do with alignments. This causes them to be ignored.

From Bill Feb 8, 07: There are many part programs where the feature nominals (stored in CAD) are not consistent with each other. In this case when we do the alignment from both the CAD to PART and the MEAS to PART, we get differing answers as far as going between MEAS and CAD. This causes the measured values to shift around with respect to the CAD. The ignore CAD to parts always forces CAD to PART to be the identity matrix. The user can then establish a machine to parts alignment and we don't care if the feature THEO's are consistent with each other. It is generally used for sheet metal where there is only one alignment in the part program to put the part in CAR body coordinate system. It is also used with parts that do not have CAD since then it does not matter if they are consistent with their feature THEO's.

Each time you create an alignment (saved or otherwise), PC-DMIS creates two transformation matrices.

1. Machine to part transformation matrix - Computed from the input features' measured values stored internally in machine coordinates.

2. CAD to part transformation matrix - Computed from the input features' theoretical values stored internally in CAD coordinates.

When you don't have available CAD data, theoretical data usually comes from the measured values of the learned features. It is difficult to get consistent results using theoretical values. This can happen when some of these values are edited, while others are not.

If you have selected the Ignore CAD to Part check box when you save an alignment, PC-DMIS ignores the CAD to part matrix and instead only saves the machine to part alignment. All theoretical values will now be in the same coordinate system.

Generally, if you are not using CAD data, select this check box.

Effects on CAD Equals Part

If you want to execute an alignment from features measured without CAD data in DCC mode and you will be using the CAD Equals Part menu option (or CAD = Part button), be sure to select the Ignore CAD to Part check box prior to setting the CAD equal to the part. For information on setting the CAD equal to the part, see the "CAD Equals Part" topic in the "Creating and Using Alignments" chapter.

Theoretical Values for Copied Features

- If you clear this check box and copy a feature to a new location in the Edit window, the theoretical values of the feature will be associated with the alignment at the feature's original location.

- If you select this check box and copy a feature to a new location in the Edit window, the theoretical values of the feature will be associated with the alignment at the feature's new location.

See "Changing Alignment Nominal Values" in the "Creating and Using Alignments" chapter.