Anchor Position and Pivot/Ceneter Position of import assets

ChSh

Hi,

There is a problem that has troubled me for long time. I am working on a project which requires placing large machine model. After placement, my Model jumped occasionally. Since I add an anchor to the model for all the elements, I found somehow the pivot of my model is really far away from the real center of model. So, I doubt that my anchor is attached to the pivot. Then it occurs the unstable placement. The question is where the anchor exactly is attached. Pivot?

Another issue is about the pivot of the import 3D .FBX model. I edit pivot with some other software. However, it doesnt't really change the pivot when I examine it after import. That is werid. Does someone has similar experience when working with a large model?

stepan_stulov

Hello, @ChSh

The question is where the anchor exactly is attached. Pivot?

Pivot is a backwards human-friendly concept that causes many misunderstandings. What's more technically straight-forward is to say where an object is and where its visual content is within it. Just think of top-down nested coordinate systems, not pivots.

World anchors neither know nor care about the visual content of your objects. Literally the only thing they do is make sure position and rotation of an object is stable to its nearest spatial surrounding. The rest is up to you. If you place the visual content within that object far away from the origin you will see all kinds of unfortunate problems like leverage effect (slight angular errors become visually bigger with distance from the origin). Your eye notices the stability issues not between the object's origin and the background environment but between what it sees and the background environment behind it. Your eye sees what it's shown and know not of coordinate systems. It's stable "here" but jitters "there".

The solution to the problem would be to place the visual content of the object so that that content's "visual centre of masses" is near/at the object's origin. This will decrease the errors but won't solve the problem for farther parts of bigger objects. For bigger objects you may need to be smarter and perhaps use multiple world anchors in the corners of the model and then do a smoothened calculation of your object's position and rotation derived from all the anchors simultaneously.

stepan_stulov

Hello, @ChSh

The question is where the anchor exactly is attached. Pivot?

Pivot is a backwards human-friendly concept that causes many misunderstandings. What's more technically straight-forward is to say where an object is and where its visual content is within it. Just think of top-down nested coordinate systems, not pivots.

World anchors neither know nor care about the visual content of your objects. Literally the only thing they do is make sure position and rotation of an object is stable to its nearest spatial surrounding. The rest is up to you. If you place the visual content within that object far away from the origin you will see all kinds of unfortunate problems like leverage effect (slight angular errors become visually bigger with distance from the origin). Your eye notices the stability issues not between the object's origin and the background environment but between what it sees and the background environment behind it. Your eye sees what it's shown and know not of coordinate systems. It's stable "here" but jitters "there".

The solution to the problem would be to place the visual content of the object so that that content's "visual centre of masses" is near/at the object's origin. This will decrease the errors but won't solve the problem for farther parts of bigger objects. For bigger objects you may need to be smarter and perhaps use multiple world anchors in the corners of the model and then do a smoothened calculation of your object's position and rotation derived from all the anchors simultaneously.