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StageFive

Cartesian Coordinates Confusion

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Hi Everyone,

Possibly I have a setting that is changing this, but I'm confused by the coordinates in C4d. I always thought that moving something to the right on the X-Axis would be a positive number, and to the left would be a negative number. That's not what I'm seeing though in the coordinates. Is there a setting somewhere for this, or is this just how it works in C4d?

Thanks,

C4d Cartesian Coordinates.png

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Moving to the right of World Center is positive values, but your current camera is aiming from behind, so moving to the right from there is actually to the left (from the front) into negative space.

 

CBR

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  • Thanks!, I wasn't sure which way is pointing forward and which is back. So the converse of that question then, is why is my Z-Axis showing a positive number when I push the mesh farther back and a negative number when I bring it forward?

    Reversed Z Axis.png

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    6 minutes ago, StageFive said:

    So the converse of that question then, is why is my Z-Axis showing a positive number when I push the mesh farther back and a negative number when I bring it forward?

     

    Nope, that's the same question and same answer, only now you've moved the camera round the front haven't you ?! So what you are thinking should be negative space actually isn't...

     

     CBR 

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    You will need to learn the difference between local and global coordinates as well as that all coordinates are either relative to the world axis or an object axis, but generally not relative to your view on the scene. Always keep in mind that your choice of view on the scene has no influence on the other objects positions.

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  • I'm in perspective. But not sure why the camera (or perspective view) has any bearing on the object location? Shouldn't it be agnostic of whatever view I'm in?

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    6 minutes ago, StageFive said:

    I'm in perspective. But not sure why the camera (or perspective view) has any bearing on the object location? Shouldn't it be agnostic of whatever view I'm in?

     I can see you're in perspective, and which way your camera is facing from the position of the world axis ! Look at the difference between your first and second screenies in that respect...

    The space itself (ie where an object is in relation to World Centre) is agnostic of which view you are in, but to move 'right' on an axis is obviously not, and that is what is causing the confusion here. Those values are absolutely what I would expect to be seeing.

     

    CBR

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  • Thanks for the feedback. I guess I'm just confused compared to most other 3d apps I've used in the last 11 years then (other than Blender). I've never had this issue in any of them. Also the transform handles don't point in the direction that I'm accustomed to (as far as I can tell). The red arrow has typically faced to the right whilst looking down Z-Negative direction (and most apps I've ever used start out with the view facing that direction and have all the Transform Handles pointing towards positive axis movement, X+=red, Y+=green, Z+=blue). 

     

    This was a new C4d scene with a new cube placed in it. I only reduced one side in scale so I could compare which way the object was facing. And if I change the coordinates from Local to World there is no change in how it displays the mesh location in the coordinates panel. 

     

    This screen recording of Modo shows how I'm expecting it to work (which is how it works in many other apps). Usually the X-Axis handle points towards X-Positive. It seems that C4d's X-Axis handle points in the opposite direction. Is this correct?

     

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    Cinema 4D is what I believe is known as a Y-Up Left-Handed coordinate system. The 'left-handed' part means that the Z axis points the opposite to most other apps like maya for example, which is Y-Up, right-handed.

    Blender & Unreal engine for their part, are Z-Up, as are most CAD apps.

    It's just differences in the default coordinates.

    Another thing to note, is in maya, the x-axis is kind of dominant, in that IK & Constraints like to assume by default that the x points down to the next joint in the chain. And possibly (I haven't used it for a while), that rotation around the x axis is dominant ie it will never cause gimbal-lock. In Cinema the z-axis serves this function & you'll notice amost of the default rigging tools assume or want to align the z-axis pointing down the chain.

    This in itself derives from the default rotation orders in the programs. Cinema's default HPB is equivalent to 1 of the 6 alternatives ie 'xyz', 'zxy' etc, I can't remember which off the top of my head. But anyway, Maya's default rotation order is a different one, hence the different dominant axis.

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    1 hour ago, StageFive said:

    It seems that C4d's X-Axis handle points in the opposite direction. Is this correct?

    No. The opposite of that should be true. The World Axis handle points toward positive space.

     

    image.thumb.png.c5a209d2846cae27a202150e6a77cf51.png

     

    Here this cube is in positive Z (and Y) space but negative X space, which is exactly what the co-ords manager confirms...

     

    CBR

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  • 16 hours ago, Decade said:

    Cinema 4D is what I believe is known as a Y-Up Left-Handed coordinate system. The 'left-handed' part means that the Z axis points the opposite to most other apps like maya for example, which is Y-Up, right-handed.

    Blender & Unreal engine for their part, are Z-Up, as are most CAD apps.

    It's just differences in the default coordinates.

    Another thing to note, is in maya, the x-axis is kind of dominant, in that IK & Constraints like to assume by default that the x points down to the next joint in the chain. And possibly (I haven't used it for a while), that rotation around the x axis is dominant ie it will never cause gimbal-lock. In Cinema the z-axis serves this function & you'll notice amost of the default rigging tools assume or want to align the z-axis pointing down the chain.

    This in itself derives from the default rotation orders in the programs. Cinema's default HPB is equivalent to 1 of the 6 alternatives ie 'xyz', 'zxy' etc, I can't remember which off the top of my head. But anyway, Maya's default rotation order is a different one, hence the different dominant axis.

     

    Perfect! Thanks for the explanation. Now it makes sense. I had studied Gimbal Lock and Euler Rotations years ago, but haven't thought much about them since. I guess I just got mostly lucky having the majority of 3d apps that are based on right handedness and took that for granted.

     

    I've known that most CAD based apps and Blender have Z Up orientation, but I've never seen much on different implementations of handedness. I'll just have to adjust for the differences, now that I know.

     

    Cheers everyone. Solved. 

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