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Hi!

I have noticed that you are able to define the threshold value used when determining if a white spot is sufficiently round to be considered a marker. In our application we use circular (ring shaped) markers of diameter approx. 18mm. These markers are surrounding a cylindrical solid object. My question is how this will affect the accuracy of the position measurement.

Consider the case when you look at the circle from a point in the circle plane, you will see a line. If the line is reduced to a point, this point will coincide with the circle center. If however you tilt the circular marker you would see an ellipse, since the object in the center of the marker is not transparent you will only see about half the ellipse. What will the location of this part ellipse be defined as?

Thank you in advance
Fredrik Bagge

Hi Fredrik,

Could you post a picture of the object you're tracking, with the markers attached to it, so we can get a better sense of your application? Also, you posted in the Camera SDK thread--are you using the Camera SDK, or one of our tracking packages like Tracking Tools?

Thank you for your reply.

We are trying to investigate what results to expect before we are constructing our ring shaped markers so they are unfortunately not available for photographing yet.

Right now we are using Tracking tools, we do however consider to implement our own algorithm using the CameraSDK.

Hi Fredrik,

Without seeing a picture of your marker setup, I can't say what you'll experience for sure. The 2D marker centroids are essentially the center of mass of the blob, whatever the shape. If you turn off the roundness filter, you could see a range of centroids like this:

Thank you!

Now I know what to expect.

Best regards,
Fredrik Bagge

How do I disable roundness filter? Is there a way to test it in visualtest.exe that comes with the sdk?
We need to distinctly identify markers from one another, object id doesn't really tell much. Is there a way to uniquely identify markers?

Thanks,
Ashutosh

Hey Fredrik,

The Camera SDK, and any of the apps in the SDK like the visualtest.exe don't do filtering of any kind.

With regards to the Camera SDK, some tracking modes transmit the overall shape of an object, others only report the roundness of an object so visualization and inspection of the shape can become difficult through the SDK.

If you are specifically looking to get the shape of an object through the Camera SDK, you will want to put the camera into the Segment or Precision video mode. Once in that mode, you can determine the shape on an object from a list of segments that are attached via a linked list to the object. If you look at the definition of a cObject, you'll see you can get Segments(). Additionally the headers gives you some additional insight. If you just want the roundness of the object you can call object->Roundness() to get a metric of roundness.

If you're talking about disabling the object filtering in the Tracking Tools application, you can go into the camera settings and in the bottom half under the point cloud you can disable the filtering. It's important to note that with or without filtering the objects are drawn regardless. When filtered there is a red X over the object.

If you need additional clarification let us know.