Strange transform.translate issue

Unity Engine
1

I’ve run into a very strange issue that suggests that I don’t yet fully understand how unity works internally, and would welcome any insight on what I got wrong.

Here’s what I’m trying to do: I have an object that I want to move in the direction that it is facing (i.e. in the direction of the transform’s ‘forward’ vector).

Here is what does NOT work but, which I thought should work (see below for what happens):

transform.Translate(transform.forward * Time.deltaTime); // translate in Forward direction

This, on the other hand, works:

transform.position = transform.position + transform.forward * Time.deltaTime;

To my uneducated mind, above two lines should have the same effect: move the object’s origin by deltaTime’s fraction of the object’s forward vector in the direction of said vector.

Using an object (no parents) with a rotation of 0,0,0 the two above code lines are exactly equivalent. So far, so good.

HOWEVER, when I cange the object’s y rotation with Editor’s Inspector, the line that uses “Translate()” results in a movement direction that is EXACTLY TWICE the amount of Y rotation, i.e. the object moves

  • ‘backwards’ (180 degrees) when it should move right (90 degrees),
  • ‘forward’ (0 = 360 degrees) when it should move back (180 degrees), and
  • right (90 degrees) when it should move ‘ahead and right’ (45 degrees).

I only use Editor to change the object’s heading, no code at all to set any rotation in C#.

So it looks as if the ‘forward’ vector is interpreted different from how I do in Translate().

So obviously, I’m not fully understanding how transform.Translate() is supposed to work. Can someone please point out what I got wrong? This is driving me nuts. The only explanation that I can think of is that Translate() takes a directional vector (in this case ‘forward’), and applies it’s internal roation to the vector before performing the translation, i.e. making the translation direction local-relative. This would account for the double rotation - but clashes with how I expect a translation to work.

Thanks,
-ch

2

Ha. Re-Re-Re-Re-reading the Docs, I realizes that I mis-interpreted the optional relativeTo Parameter. Silly me. Translate() defaults to the object’s relative axes (Space.Self), not global (which requires Space.World as additional parameter).

So it looks as if I should be more careful when reading the docs.