TypeError: float() argument must be a string or a number

asked 2019-05-24 22:17:45 -0600

A_YIng gravatar image

Hello, I follow this repo and want to combine it to my robot.

But when I try to get the rotation and convert it to Quaternion. I encounter the error below:

 cyc@cyc-X550JX:~$ rosrun gpd test_grasp.py 
[INFO] [1558753204.760210]: Start to get grasp data...
[INFO] [1558753209.430311]: Received 1 grasps.
[x: 0.527165424825
y: 0.842580358548
z: 0.110249509106
 x: 0.849633644563
y: -0.524891291709
z: -0.0511057914036
 x: 0.0148082712001
y: 0.120612898469
z: -0.992589161651]
Traceback (most recent call last):
  File "/home/cyc/catkin_ws/src/gpd/src/test_grasp.py", line 74, in <module>
    qua_R = tf.transformations.quaternion_from_matrix(R)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/tf/transformations.py", line 1206, in quaternion_from_matrix
    M = numpy.array(matrix, dtype=numpy.float64, copy=False)[:4, :4]
**TypeError: float() argument must be a string or a number**

Here is my code and the GraspConfig information:

#!/usr/bin/env python
import rospy
import sys
import tf
import numpy as np
from gpd.msg import GraspConfigList
from tf.transformations import quaternion_from_matrix
from geometry_msgs.msg import Pose
from geometry_msgs.msg import PoseStamped 

grasps = []

def callback(msg):
    global grasps
    grasps = msg.grasps

# Create a ROS node.
rospy.loginfo('Start to get grasp data...')

# Subscribe to the ROS topic that contains the grasps.
sub = rospy.Subscriber('/detect_grasps/clustered_grasps', GraspConfigList, callback)

# Wait for grasps to arrive.

while not rospy.is_shutdown():    
    if len(grasps) > 0:
        top_grasp = grasps[0] # grasps are sorted in descending order by score.
        rospy.loginfo('Received %d grasps.', len(grasps))

        R = (top_grasp.approach, top_grasp.binormal, top_grasp.axis)
        R = np.asarray(R)

        qua_R = tf.transformations.quaternion_from_matrix(R)
        print qua_R



Hope you guys can help me, thanks a lot!

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The quaternion_from_matrix method is expecting a 3x3 rotation matrix, you appear to be passing it something very different here.

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-05-25 09:43:55 -0600 )edit

I copy the partial information from GraspConfig.msg :

# Orientation represented as three axis (R = [approach binormal axis])
geometry_msgs/Vector3 approach # The grasp approach direction
geometry_msgs/Vector3 binormal # The binormal
geometry_msgs/Vector3 axis # The hand axis

So, I think the R = (top_grasp.approach, top_grasp.binormal, top_grasp.axis) should be a 3x3 roatation matrix. Does it have any mistakes in this ? Thanks for your reply !

A_YIng gravatar image A_YIng  ( 2019-05-25 11:45:19 -0600 )edit

Okay I think I can see the problem. quaternion_from_matrix is expecting a 3x3 numpy array. But looking at the value printed out you're passing it something else. I think the three values approach, binormal, and axis are dictionaries not lists so you'll have to extract each element individually.

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-05-27 06:01:09 -0600 )edit

Actually, I created a 3x3 Numpy matrix to storage the vector of three data today. But quaternion_from_matrix occur the error about matrix index is out of bound, although I used matrix.shape to check before, it still not working. I tried convert to Euler first, then convert the output to Quaternion. Finally, it works. Thanks for your patience.

A_YIng gravatar image A_YIng  ( 2019-05-27 10:19:46 -0600 )edit