Hello all,
I've got a 3D world using the right-handed coordinate system with X to the right, Y up and Z outof the screen, the horizontal direction going counter-clockwise over the Y axis, and the vertical direction also counter-clockwise over the X axis.
My question is, where are both rotations starting ? Currently I have looking over the negative Z axis as zero for both (conforming with the direction I look in when looking at the screen).
The thing is, I could easily imagine someone regarding the X axis as the
most important one (making my horizontal direction -90 degrees) and possibly having straight up as zero degrees (making my vertical direction +90 degrees).
tl;dr:
Whats the convention in regard to where both the horizontal and vertical directions start ?
Regards,
Rudy Wieser
I was a little bit surprise about how the angle is measured and[snip image]
what the zeroth axis is.
Here is the full article.[snip link]
Paul,
I was a little bit surprise about how the angle is measured and[snip image]
what the zeroth axis is.
I'm sorry, but that image tells me nothing about what I am looking for.
Just how that "x" point is oriented related to the two axis nearest to it. IOW, they might well be an arbitrary choice (if the X coordinate would be negative would phi become larger than 90 degrees, or would it be measured from the negative X axis ? If the Z coordinate would be smaller, would theta than described as over 45 degrees, or would it than be measured from the horizontal plane ?).
Yes, I know nothing about any kind of convention in that regard. Not even
if there is one and/or if its applicable to that image. :-(
Also, its shows a Z=up space not related to anything, while mine is a Y=up space related to a computers screen, andI'm not at all sure that that difference doesn't change anything ...
Here is the full article.[snip link]
I've tried to read and understand it, but not even the "Conventions" chapter is specific about it :
"where the "zenith" direction is north and positive azimuth (longitude) angles are measured eastwards *from some prime meridian*. "
(emphasis mine)
Besides that I would need to assume that a meridian (as used on a spherical thing like our earth) may be considered to be the same as an axis in a flat (computer game) world, my largest problem is that I do not see anything
about what that "prime meridian" than might be. :-|
... or at least, I do not recognise anything as such.
Regards,
Rudy Wieser
Your choices of labeling are not arbitrary, if you expect to
use someone elses library of coordinate transforms.
The first question is, can you take the Wiki diagram and rotate
it so it overlays your Y-up diagram ?
If so, then the measurement of Theta and Psi are in the diagram and that's how
you measure them.
But then I test. I see whether the results make "intuitive sense".
I swallow my sense of unreality, if the transforms test and work.
Hello all,There are likely hundreds of coord system variants all using an
I've got a 3D world using the right-handed coordinate system with X to the right, Y up and Z outof the screen, the horizontal direction going counter-clockwise over the Y axis, and the vertical direction also counter-clockwise over the X axis.
My question is, where are both rotations starting ? Currently I have looking over the negative Z axis as zero for both (conforming with the direction I look in when looking at the screen).
The thing is, I could easily imagine someone regarding the X axis as the
most important one (making my horizontal direction -90 degrees) and possibly having straight up as zero degrees (making my vertical direction +90 degrees).
tl;dr:
Whats the convention in regard to where both the horizontal and vertical directions start ?
Regards,
Rudy Wieser
It sounds like you are using some sort of 3D Cartesian system.
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