GetVelocityAtPosition returns incorrect values for non-rootpart rotating assemblies

Bug Reports Engine Bugs
#1

Reproduction Steps
Using the GetVelocityAtPosition() method on a base part will produce nonsense results if it is not the root part of its assembly and that assembly is rotating.


This video visualises the problem: The blue arrows are the correct velocity at the point it originates from, the red arrows are what GetVelocityAtPosition() returns at that same point, and purple means the two are identical. The blue parts have root priority.

It can be seen that GetVelocityAtPosition() returns correct values for the root parts and parts with only linear velocity, but incorrect results for non-root parts. Repro file attached.
VelocityBugRepro.rbxl (37.3 KB)

Issue Area: Engine
Issue Type: Other
Impact: Low
Frequency: Constantly

3 Likes
#2

I see the simple math mistake that caused this. Thanks for the clear repro, fixing it.

TL;DR: The code accidentally applies the position you pass relative to the part you called the function on rather than the root around which the angular velocity is hence the root dependent behavior.

4 Likes
#3