# "How to accurately measure OD and ID of a circular part using VMeasurement in B&R mapp Vision?" **URL:** \ **Category:** Controls & Vision\ **Tags:** mapp-vision\ **Created:** [June 1, 2026, 6:34am UTC](https://community.br-automation.com/t/how-to-accurately-measure-od-and-id-of-a-circular-part-using-vmeasurement-in-b-r-mapp-vision/11407 "2026-06-01T06:34:57Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Black\_Cho](https://avatars.discourse-cdn.com/v4/letter/b/FF8800/32.png) [@Black\_Cho](https://community.br-automation.com/u/Black_Cho)\ **Post date:** [June 1, 2026, 6:34am UTC](https://community.br-automation.com/t/how-to-accurately-measure-od-and-id-of-a-circular-part-using-vmeasurement-in-b-r-mapp-vision/11407/1 "2026-06-01T06:34:57Z")
Hello, I am currently using the **VMeasurement Function Block** in B&R mapp Vision to measure the outer diameter (OD) and inner diameter (ID) of a circular part (washer). My current approach is to use **Edge Model Mode** to detect edge points on the outer and inner contours, and then calculate the diameter using the `distance_cog` operation. However, as shown in the attached image, the detected edge points are not always located at the positions I expect. As a result, the measured OD and ID values contain errors and are not consistent. ### Current Configuration - Function: VMeasurement - Model Type: Edge Model Mode - Measurement Method: Edge point detection followed by `distance_cog` - Target: Outer diameter (OD), inner diameter (ID), and thickness of a washer ### Issue - The detected edge points are not located exactly opposite each other with respect to the circle center. - Measurement results vary depending on the detected edge locations. - It is difficult to obtain stable and accurate diameter measurements. ### Questions 1. Is there a recommended way to accurately measure the OD and ID of a circular part using only VMeasurement? 2. What Function Blocks or measurement methods are commonly used for OD/ID measurement of circular parts in mapp Vision? 3. Is there a better approach than Edge Model Mode, such as circle fitting or blob-based measurement? 4. What is the recommended method for achieving subpixel-level accuracy when measuring OD and ID? I have attached screenshots of my current configuration and measurement results for reference. Any advice or best practices would be greatly appreciated. Thank you. [-2109032814.bmp](https://community.br-automation.com/uploads/short-url/s0xaVLyrFvbDLwlqzojEZH3wgeg.bmp) (5.1 MB) [-1848255911.bmp](https://community.br-automation.com/uploads/short-url/3yStG7eG9lzJD2SB07XtD808V7m.bmp) (5.1 MB) ![20260601_153101](https://europe1.discourse-cdn.com/brcommunity/original/2X/f/ff7d40c33906904097427dd3fb1a47e56a45f48d.jpeg) ---
**Author:** ![bryan.olson](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/bryan.olson/32/2155_2.png) [@bryan.olson](https://community.br-automation.com/u/bryan.olson)\ **Post date:** [June 2, 2026, 4:54pm UTC](https://community.br-automation.com/t/how-to-accurately-measure-od-and-id-of-a-circular-part-using-vmeasurement-in-b-r-mapp-vision/11407/2 "2026-06-02T16:54:01Z")
Hi, I would think the Circle model in the Measurement VF would work, have you tried that? I have also used Matching on things like this, with a model of one of the edges (A ring, not a donut model). Matching has a lot of parameters to choose how picky it is with the bumpy edges and what contrast it requires, and if you open up the MinScale and MaxScale you can get a Scale output which can be converted to a measurement if you know how large Scale=1.00 is. ---
**Author:** ![kovarj](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/kovarj/32/537_2.png) [@kovarj](https://community.br-automation.com/u/kovarj)\ **Post date:** [June 22, 2026, 5:51am UTC](https://community.br-automation.com/t/how-to-accurately-measure-od-and-id-of-a-circular-part-using-vmeasurement-in-b-r-mapp-vision/11407/3 "2026-06-22T05:51:56Z")
Hi @Black_Cho , what is status of your topic, can you update us? ---
**Author:** ![Black\_Cho](https://avatars.discourse-cdn.com/v4/letter/b/FF8800/32.png) [@Black\_Cho](https://community.br-automation.com/u/Black_Cho)\ **Post date:** [June 24, 2026, 6:26am UTC](https://community.br-automation.com/t/how-to-accurately-measure-od-and-id-of-a-circular-part-using-vmeasurement-in-b-r-mapp-vision/11407/4 "2026-06-24T06:26:04Z")
Hi @**[Jaroslav Kovar](https://community.br-automation.com/u/kovarj),** I will conduct some tests based on your recommendations above and will contact you again if I have any further questions. Thank you for your support.