Hey, I'm working on a object recognition framework that uses deep learning methods. Given the locations of the objects in the image (bounding box), I use the PointCloud publised by a Kinect 2, to locate those.

Currently, I'm working with ROS Kinetic and I'm developing in python.

Sometimes, trying to obtain the xyz points of the bounding box, using the read_points method I receive the following error:

File "/home/some1/catkinws/src/semmapperisr/semmappermarkers/nodes/objectmapper.py", line 205, in getobject3Dpoints points = np.array(list(pc2.readpoints(self.currpc,fieldnames = ("x", "y", "z"), skipnans=True, uvs=bbpts))) File "/opt/ros/kinetic/lib/python2.7/dist-packages/sensormsgs/pointcloud2.py", line 83, in readpoints p = unpackfrom(data, (rowstep * v) + (pointstep * u)) error: unpack_from requires a buffer of at least 12 bytes

This error doesn't happen everytime I try to obtain the xyz points. Sometimes, there is no problem. The code is extensive, I will try to show their important parts for this case.

Imports:

import rospy
from sensormsgs.msg import PointCloud2, PointField
import sensormsgs.point_cloud2 as pc2

PointCloud Callback definition:

self.pcxyzsub = rospy.Subscriber(subpointcloudtopic, PointCloud2, self.pointcloudcallback, queuesize=2)

PointCloud Callback:

def pointcloudcallback(self, pointcloudmsg):
    self.pcmessagelocker.acquire()
    self.currpc = pointcloudmsg
    self.pcmessagelocker.release()

Where I try to obtain the xyz points:

def getobject3Dpoints(self,widthmin,widthmax,heightmin,heightmax,viewpath):
    bbpts=((i,j) for i in xrange(widthmin,widthmax+1) for j in xrange(heightmin, heightmax+1))#pixels of the image to verify in the pointcloud
    self.pcmessagelocker.acquire() #lock the pc message -> dont change/access current pc message at same time
    points = np.array(list(pc2.readpoints(self.currpc,fieldnames = ("x", "y", "z"), skipnans=True, uvs=bbpts)))
    self.pcmessagelocker.release()

I'm subscribing to the camera/depth_registered/points published by openni using Kinect.

I searched for that problem with the unpack and found nothing until now, do you have any idea what can be happening? Thanks for your patience, SancheZ