# Revision history [back]

It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

from std_msgs.msg import String, Header, Float32MultiArray, MultiArrayDimension

#initialization, etc.

self.scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes)
for i in range(0,len(dims)):
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].stride = 1
scoresmsg.layout.dim[i].label = 'dim_%d'%i
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32')
self.scores_pub.publish(scoresmsg)


I haven't written a subscriber for this to see if the indexing works as intended.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]


It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

import rospy
import numpy as np

from std_msgs.msg import String, Header, Float32MultiArray, MultiArrayDimension

#initialization, etc.

self.scores_pub scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes)
#for loop should be rather fast. it just gets the number of dimensions of your nparray to construct the message
for i in range(0,len(dims)):
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].stride = 1
scoresmsg.layout.dim[i].label = 'dim_%d'%i
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32')
self.scores_pub.publish(scoresmsg)
np.frombuffer(scores.tobytes(),'float32') ## serializes
scores_pub.publish(scoresmsg)


I haven't written a subscriber for this to see if the indexing works as intended.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]


It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

import rospy
import numpy as np

from std_msgs.msg import Float32MultiArray, MultiArrayDimension

#initialization, etc.

scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes)
#for loop should be rather fast. it just gets the number of dimensions of your nparray to construct the message
for i in range(0,len(dims)):
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i]
scoresmsg.layout.dim[i].stride = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].stride = 1
scoresmsg.layout.dim[i].label = 'dim_%d'%i
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32') ## serializes
scores_pub.publish(scoresmsg)


Attention: I haven't written a subscriber for this to see if the indexing works as intended. intended. The data is preserved which is the most important part, but the stride sizes are still an issue. I will write an example listener and double check this soon.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]


It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

import rospy
import numpy as np

from std_msgs.msg import Float32MultiArray, MultiArrayDimension

#initialization, etc.
def talker():

scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
#if the dimensions vary, then the the layout will need to be updated as well
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes)
#for loop should be rather fast. it just gets the number of dimensions of your nparray to construct the message
for i in range(0,len(dims)):
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i]
scoresmsg.layout.dim[i].stride = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].label = 'dim_%d'%i

while not rospy.is_shutdown():
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32') ## serializes
scores_pub.publish(scoresmsg)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


Attention: I haven't written a subscriber for this to see if the indexing works as intended. The data is preserved which is the most important part, but the stride sizes are still an issue. I will write an example listener and double check this soon.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]


It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

import rospy
import numpy as np

from std_msgs.msg import Float32MultiArray, MultiArrayDimension

def talker():
rospy.init_node('talker', anonymous=True)
scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
#if the dimensions vary, then the the layout will need to be updated as well
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes)
#for loop should be rather fast. it just gets the number of dimensions of your nparray to construct the message

for i in range(0,len(dims)):
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i]
scoresmsg.layout.dim[i].stride = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].label = 'dim_%d'%i

while not rospy.is_shutdown():
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32') ## serializes
scores_pub.publish(scoresmsg)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


Attention: I haven't written a subscriber for this to see if the indexing works as intended. The data is preserved which is the most important part, but the stride sizes are still an issue. I will write an example listener and double check this soon.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]


It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistake

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

import rospy
import numpy as np

from std_msgs.msg import Float32MultiArray, MultiArrayDimension

def talker():
rospy.init_node('talker', anonymous=True)
scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
#if the dimensions vary, then the the layout will need to be updated as well
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes)
#for loop should dims.prod()/float(scores.nbytes) # this is my attempt to normalize the strides size depending on .nbytes. not sure this is correct

for i in range(0,len(dims)): #should be rather fast. it just
# gets the number num. of dimensions dims of your nparray to construct the message

for i in range(0,len(dims)):
message
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i]
scoresmsg.layout.dim[i].stride = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].label = 'dim_%d'%i

while not rospy.is_shutdown():
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32') ## serializes
scores_pub.publish(scoresmsg)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


Attention: I haven't written a subscriber for this to see if the indexing works as intended. The data is preserved which is the most important part, but the stride sizes are still an issue. I will write an example listener and double check this soon.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]


It is kind of hacky, but the way I solved this problem was by using sensor_msgs.msg.Image and cvbridge instead of the numpy message. OpenCV Mats in python are just numpy matrices and I am not even sure they need to be the same size every time you publish them, so that gives you a lot of flexibility. Here is a sample code for this idea:

import rospy
import numpy as np
from cv_bridge import CvBridge, CvBridgeError
from sensor_msgs.msg import Image

def talker():
rospy.init_node('talker', anonymous=True)
mat_pub = rospy.Publisher("matrix", Image, queue_size=1)
mybridge = CvBridge()
rate = rospy.Rate(1)

mymat = np.ones([1,4],dtype=np.int16

while not rospy.is_shutdown():
try:
mat_pub.publish(mybridge.cv2_to_imgmsg(mymat))
rate.sleep()
except CvBridgeError as e:
rospy.logerr(e)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


I suppose to publish more messages you can publish them separately and then read them in synch using message_filters and read them both at the same time (see http://wiki.ros.org/message_filters). I know this is not ideal, but how this is one way I managed to get around this. If anyone knows a better solution, please post as well!

Ps: I didn't test the code I just wrote, so there might be a silly mistakethis.

@gvdhoorn pointed out that this seemed like a misuse of a sensor_msgs/Image type, and I guess I have to agree. Another solution - the one I took in the end - is to use the MultiArray definitions. I haven't found an example in python, so here is mine:

import rospy
import numpy as np

from std_msgs.msg import Float32MultiArray, MultiArrayDimension

def talker():
rospy.init_node('talker', anonymous=True)
scores_pub = rospy.Publisher("scores",Float32MultiArray, queue_size=1)

scores = np.array([[[1.,2.],[3.,4.],[5.,6.]],[[11.,12.],[13.,14.],[15.,16.]]],dtype='float32')
#if the dimensions vary, then the the layout will need to be updated as well
scoresmsg = Float32MultiArray()
scoresmsg.layout.dim = []
dims = np.array(scores.shape)
scoresize = dims.prod()/float(scores.nbytes) # this is my attempt to normalize the strides size depending on .nbytes. not sure this is correct

for i in range(0,len(dims)): #should be rather fast.
# gets the num. of dims of nparray to construct the message
scoresmsg.layout.dim.append(MultiArrayDimension())
scoresmsg.layout.dim[i].size = dims[i]
scoresmsg.layout.dim[i].stride = dims[i:].prod()/scoresize
scoresmsg.layout.dim[i].label = 'dim_%d'%i

while not rospy.is_shutdown():
scoresmsg.data = np.frombuffer(scores.tobytes(),'float32') ## serializes
scores_pub.publish(scoresmsg)

if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass


Attention: I haven't written a subscriber for this to see if the indexing works as intended. The data is preserved which is the most important part, but the stride sizes are still an issue. I will write an example listener and double check this soon.

The output is:

layout:
dim:
-
label: "dim_0"
size: 2
stride: 48
-
label: "dim_1"
size: 3
stride: 24
-
label: "dim_2"
size: 2
stride: 8
data_offset: 0
data: [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0]