#### Start and End Angles

For a circular feature, the different Start Angle and End Angle boxes define where PC-DMIS probes the feature. For many situations the default values are sufficient, but there may be times when you need to measure a circular feature that is partially obstructed by another feature or otherwise only partially available for probing. In version 4.2 and later you should enter the start and end angles in a counter-clockwise manner.

Start and End Angle Examples

For example, if you measure a hole with six hits and a Start Angle of 0 and an End Angle of 360, it will look something like this:

Notice that the Start Angle and the End Angle are the same: 0 and 360. Also, the six points making up the circle feature are equally distributed between the two angles. In this case each point is taken at 60 degree intervals with the last point taken at 300 degrees.

However, changing the Start Angle to 45 (red arrow) and the End Angle to 270 (orange arrow) limits the hits to a certain portion of the circular feature:

Start and End Angle Boxes

Angle Type | Description | Notes
Start Angle and End Angle boxes | These boxes let you change the default starting and ending angles on the feature. This is a user supplied angle in decimal degrees. The starting and ending angles are relative to the values in the IJK Angle Vector boxes. If you rotate the view of the feature so that you look down its center, PC-DMIS will space the desired number of hits beginning at the Start Angle in a counterclockwise direction around the centerline until it reaches the End Angle as shown in this example:

Suppose you have a sphere feature with a Start Angle of 0, an end angle of 90, and an IJK Angle Vector of 1,0,0 (along the X+ axis). The starting and ending angles are relative to the angle vector. Measurement will proceed in a counterclockwise manner, equally spaced between 0 and 90 degrees:

Screen capture of an Auto Sphere showing path lines and hit locations from Start Angle of 0 (at A) and End Angle of 90 (at B).

These boxes are only available for Circle, Cylinder, Ellipse, Cone, and Sphere auto features.

Start Angle 2 and End Angle 2 boxes | The Start Angle 2 and End Angle 2 boxes let you determine the secondary starting and ending angle on a sphere feature. This angle is in decimal degrees. The secondary angle, if looking at a side view of a sphere, starts at the sphere's equator and then moves towards the top pole as the angle increases to 90 degrees and then back down to the equator on the opposite side of the sphere at 180 degrees.

These angles allow you to place the hits in an area where the probe can reach them without obstruction.

Consider this example:

Suppose you have an external sphere that's halfway visible above the surrounding surface. If you use a Start Angle 2 value of 0 degrees, the probe would collide with the surrounding surface when it attempted to take the hits around the sphere's equator. A slight adjustment in the Start Angle 2 value will resolve this problem.

If you create the sphere with 20 hits, and give it a Start Angle of 45, an End Angle of 270, a Start Angle 2 of 20, and an End Angle 2 to 90, PC-DMIS would space 19 hits around the sphere 20 degrees up from the equator of the sphere like this:

A Top View of the Sphere | A Side View of the Sphere

This provides the probe with plenty of room to measure the sphere. The sphere's second level would only consist of one hit on top of the sphere.

If you adjusted End Angle 2 to something like 110 degrees, the second level of hits would have 5 hits adjusted 20 degrees down from the top of the sphere:

This box is only available for Sphere auto features.

2 Degree Buffer Offset: When generating an arc using one of the circular auto features (Circle, Cylinder, Cone, Sphere, or Round Slot), PC-DMIS will offset the start and end angles each by two degrees. This way arcs retrieved from the CAD aren't probed on their starting and ending angles, possibly catching a corner. This shouldn't be an issue for the most part unless you are attempting to generate a small arc of only a few degrees. For example, if you want to generate a four degree arc of an Auto Circle you will need to type in an eight degree arc parameter in the Start Angle and End Angle boxes, knowing that PC-DMIS will shorten the arc by two degrees on each angle.