This table summarizes how different combinations of primary, secondary, and tertiary datums are used to create GD&T datums in True Position and Profile items. Note that:
- Adjusting a vector means that the vector is reversed if the approximate direction of the vector in the Workplane item is one of X-, Y-, or Z-.
- If an axis is parallel to a plane, the axis lies on the plane.
- If an axis is perpendicular to a plane, the axis intersects the plane.
|
Primary Datum (A) |
Secondary Datum (B) |
Tertiary Datum (C) |
How the Datum is Built |
Fully Determined? |
|
Plane |
Plane |
Plane |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector of the intersection of A and B. The origin is the intersection of the X axis with C. All three planes must intersect. |
Yes |
|
Plane |
Plane |
Axis |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector of the intersection of A and B. The origin is at the intersection of C with A if C is perpendicular to A; it is at the intersection of C with B, projected onto A, if C is parallel to A. Planes A and B must intersect. |
Yes |
|
Plane |
Plane |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector of intersection of A and B. The origin of the datum is the origin of the Workplane. B must intersect A. |
No |
|
Plane |
Axis |
Plane |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector of intersection of A and C. The origin is at the intersection of B with A. B must intersect A; C must intersect A. |
Yes |
|
Plane |
Axis perpendicular to A |
Axis perpendicular to A |
The Z axis of the datum is the normal of the A plane. The X axis is taken from the workplane (made perpendicular to the Z axis of the datum). The origin is at the intersection of B with A. Axis C is used to orient the circle or point features relative to the Z plane of the datum. It is not used to calculate the datum. |
No |
|
Plane |
Axis perpendicular to A |
Axis parallel to A |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector from projecting C onto A. The origin is at the intersection of B with A. |
Yes |
|
Plane |
Axis parallel to A |
Axis perpendicular to A |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector from projecting B onto A. The origin is at the intersection of C with A. |
Yes |
|
Plane |
Axis parallel to A |
Axis parallel to A |
Not supported |
|
|
Plane |
Axis perpendicular to A |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is perpendicular to the Z axis of the Workplane. The origin is at the intersection of B with A. |
No |
|
Plane |
Axis parallel to A |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector from projecting B onto A. The origin is at the origin of the Workplane. |
No |
|
Plane |
Unspecified |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum and origin are taken from the Workplane. |
No |
|
Axis |
Plane perpendicular to A |
Plane |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector from the intersection of C with the A plane. The origin is at the intersection of B with A. C must intersect the A plane. |
Yes |
|
Axis |
Plane parallel to A |
Plane |
Not supported |
|
|
Axis |
Plane |
Axis |
Not supported |
|
|
Axis |
Plane perpendicular to A |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is perpendicular to the Z axis of the Workplane. The origin is set to the intersection of B with A. |
No |
|
Axis |
Plane parallel to A |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum is the adjusted vector from the intersection of B with the A plane. The origin is not set correctly. |
No |
|
Axis |
Plane other orientation |
Unspecified |
Not supported |
|
|
Axis |
Axis |
Any |
Not supported |
|
|
Axis |
Unspecified |
Unspecified |
The Z axis of the datum is the normal of the A plane. The X axis of the datum and origin are taken from the Workplane. |
No |
|
Unspecified |
Unspecified |
Unspecified |
The datum is the Workplane datum, but with the freedom to rotate and translate in all axes. |
No |