#### Description of Target for T Value

The T Value is always the magnitude (or length) of the vector from the probe tip to a target point. The target point is determined by the Centroid, Surface/Edge, or Vector option buttons located in the Target area of the Probe Readout Setup dialog box.

- If you selected Centroid or Vector, PC-DMIS uses the distance from the probe's center point.

- If you selected Surface Edge, PC-DMIS uses the probe-compensated distance.

During Execution with "Closest Feature" and "Centroid" Selected:

The Centroid is the feature's center. While this makes more sense for some features than others, all features have a center. For the nine basic feature types, the center for each is defined below with illustrations where necessary.

- Point

  The T value is the distance to the point itself.

- Line

  The T value is the distance to the midpoint between the two outermost hits on the line segment.

- Plane

  The T value is the distance to the center of the plane. The center is the midpoint of the polygon defined by the bounding hit points defining the plane.

- Circle

  The T value is the distance to the circle's centroid.

- Round and Square Slots

  The T value is the distance to the midpoint of the slot’s plane.

- Sphere

  The T value is the distance to the center of the sphere.

- Cylinder

  The T value is the distance to the center of the top of the cylinder:

- Cone

  The T value is the distance to the cone's vertex.

During Execution with "Closest Feature" and "Surface/Edge" Selected:

When locating the surface/edge, the target for the T value is the point on the feature that is closest to the probe. For 3D features, the closest point will be on the surface of the feature; for 2D features, it will be on the edge. For the nine basic feature types, the center for each is defined below with illustrations where necessary.

- Point

  The T value is the distance to the point itself.

- Line

  The T value is the distance to the closest point on the line defined by two or more hits. This is not a line segment but a true geometric line. The example below shows two different cases.

- Plane

  The T value is the distance to the closest point on the geometric plane defined by the three or more hits.

- Circle

  The T value is the distance to the closest point on the circle's edge.

- Round and Square Slots

  The T value is the distance to the closest point on the slot's edge.

- Sphere

  The T value is the distance to the closest point on the sphere's surface. The illustration below shows the point on the surface of an outer feature, but an inner feature works the same and uses an inner surface.

- Cylinder

  The T value is the distance to the closest point on the surface of the cylinder. The illustration below shows the point on the surface of an outer feature, but an inner feature works the same and uses an inner surface.

- Cone

  The T value is the distance to the closest point on the surface of the cone (not the geometric cone). The illustration below shows the point on the surface of an outer feature, but an inner feature works the same and uses an inner surface.

During Execution with "Closest Feature" and "Vector" Selected:

When locating the vector, the target for the T value is the point on the feature vector closest to the probe. For the nine basic feature types, the center for each is defined below with illustrations where necessary.

- Point

  The T value is the distance to the closest point on the point's hit vector.

- Line

  The T value is the distance to the closest point along the line's vector.

- Plane

  The T value is the distance to the closest point on the plane's normal vector that is anchored to the plane's center (see the Plane Centroid example above for a description of the plane's center).

- Circle

  The T value is the distance to the closest point on circle's normal vector that is anchored to the circle's center point.

- Round and Square Slots

  The T value is the distance to the closest point on the normal vector of the slot's plane. The plane is defined by the slot's hit points. See the Plane Vector example above. As with that example, the normal vector is anchored to the center point of the slot's plane.

- Sphere

  The T value is the distance to the closest point on the sphere's normal vector. The vector is the same as the defined work plane or reference plane.

- Cylinder

  The T value is the distance to the closest point on the cylinder's central axis vector:

- Cone

  The T value is the distance to the closest point on the cone's central axis vector:

No Execution with "Closest CAD" Selected:

This is the only time that T, DX, DY, and DZ will show meaningful values while not executing. These show the distance to the closest point on the closest CAD surface. There must be surface CAD data, and you must set your view to Surface Mode for this to work.

During Execution with "Executing Feature" and "Surface/Edge" Selected:

This mode is for backwards compatibility, and is the original functionality. In this state, the target point is the distance to the next hit on the feature.

During Execution with "Executing Feature" and "Surface/Edge" Selected:

If you selected Centroid or Vector, these options behave as the "Closest Feature" examples above, but they show distances to the next executing feature.