Orientation Vector

A description of Viam’s orientation vector method.

Viam’s orientation vector is a method for describing the orientation of an object in 3D space. It is part of a Pose which also includes the position in 3D space.

Basics

Orientation vectors are composted of 4 attributes.

  • RX, RY, RZ - define a vector from the center of the object to another point in the reference frame. This defines the direction something is pointing in.
  • Theta - describes the angular position around that vector.

Examples

Configuring frame for a camera

  • You have a room with a camera.
  • The corner of the room is (0,0,0).
  • You want to configure the camera into the frame system, so you need to know where in the room the camera is, and where it’s pointing.
  • This requires a Pose.
  • X, Y, Z are simply the measurements from the corner of the room.
  • Now to figure out the orientation vector:
    • To figure out RX, RY, RZ first take a picture with the camera.
    • Determine the point in the very center of the image.
    • Measure the X, Y, Z of that point from the corner (call them X2, Y2, Z2, respectively).
    • RX, RY, RZ become the difference between X, Y, Z (the camera’s position) and X2, Y2, Z2 (that point’s position).
    • Theta is determined by looking at the picture and changing Theta’s value until down is correct, likely 0, 90 or 180.
      • To do this, take a picture
      • Determine if the orientation is correct
      • If not, add 90 to Theta, and try again camera example

Why we like it

  • Easy to measure in the real world
  • No protractor needed
  • Rotation is pulled out (as Theta) which is often used independently and measured independently.