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+--- Thread: Python API Pose gives odd behavior (/Thread-Python-API-Pose-gives-odd-behavior)
Python API Pose gives odd behavior-chris_UW-04-29-2020
I Have the following test code block
Code:
from robodk import Pose
def test(abc):
a,b,c = abc
p = Pose(0,0,0,a,b,c)
print (p)
test((30,89,0))
test((30,90,0))
Code:
Pose(0.000, 0.000, 0.000, 30.000, 89.000, 0.000):
[[ 0.017, -0.000, 1.000, 0 ],
[ 0.500, 0.866, -0.009, 0 ],
[ -0.866, 0.500, 0.015, 0 ],
[ 0, 0, 0, 1 ]]
Pose(0.000, 0.000, 0.000, 0.000, 90.000, 30.000):
[[ 0.000, -0.000, 1.000, 0 ],
[ 0.500, 0.866, -0.000, 0 ],
[ -0.866, 0.500, 0.000, 0 ],
[ 0, 0, 0, 1 ]]
Note the angles of the two outputs. In the second Rx and Rz appear to be swapped.
Perhaps I don't understand the coordinates but the second output seems wrong to me.
Can anyone confirm that this is bad behavior or explain why its not?
RE: python API Pose() gives odd behavior-Albert-04-29-2020
This is not a bug or a bad behavior. The Pose command uses an Euler angle representation (Rx->Ry'->Rz''). Using this representation, when the Ry value is 90 deg (your b value), Rx and Rz are redundant.
These 2 transformations are very similar:
Code:
from robodk import *
pose1 = Pose(0.000, 0.000, 0.000, 30.000, 89.000, 0.000)
pose2 = Pose(0.000, 0.000, 0.000, 0.000, 90.000, 30.000)
# Calculate error:
pose1to2 = pose1.inv() * pose2
print(pose1to2)
# Outputs: Pose(0.000, 0.000, 0.000, -0.000, 1.000, -0.000)
The 4x4 matrix you see is a pose and it represents the 6D transformation. You can see a very small change between the 2 poses.
More information here:
//m.sinclairbody.com/doc/en/PythonAPI/robodk.html#robodk.Pose
//m.sinclairbody.com/doc/en/Basic-Guide.html#RefFrames
//m.sinclairbody.com/blog/robot-euler-angles/
Albert