# Expert's Desk

by Andrew Scarella on July 28, 2016 From Ask The Experts

As a valued customer, we always want you to know the latest updates of what we are working on to continue to help you measure. Here are some updates on your favorite products right from the expert's desk.

Tech Corner

A Circle Technique that is too Clever by Half.
How do I construct a circle from 2 halves of a circle, that were measured as AUTOCIRCLES, with two different tips?

Typically, a constructed best fit circle needs at least 3 inputs to be calculated. This article shows steps to use 2 Autocircles to construct 1 best fit circle.

In the example below, the shaft mounted onto the machine has a front OD (outside diameter) which is being measured from 2 tip angles.  Each angle will scan half the circle of the OD.

Steps:

1. Create the first AUTOCIRCLE with desired parameters. This example uses an adaptive circle scan measurement strategy.

2. Create the other half of the circle using AUTOCIRCLE with the desired parameters. This example uses an adaptive circle scan measurement strategy.

3. Construct a CAST circle by selecting one of the two halves.

4. The created constructed circle will not be the desired result. Edits must be made.

5. Hover the cursor over CAST and change the construction type to BEST FIT (BF).

6. Edit the CIR32 inputs to include the individual hits from the two semi-circles, CIR32_1 and CIR32_2.

CIR32_1.HITS[1..CIR32_1.NUMHITS],CIR32_2.HITS[1..CIR32_2.NUMHITS],,

7. This is the desired circle. Review the resulting constructed feature coordinate axes and diameter values to ensure that they are within expectations (an error typing inputs can produce a solution which may be mathematically correct, but not intended).

Now you have a constructed circle from 2 halves of a circle. To get more PC-DMIS tips and tricks, check out our knowledgebase section located here

#### Andrew Scarella

Andrew Scarella is the Digital Marketing Manager for Hexagon Manufacturing Intelligence North America. He contributes to this blog as well as updates the North American website and provides content for the company social media channels including Facebook, Twitter and LinkedIn.