MATLAB Answers

How do I get readImage (ROS) to work?

조회 수: 66(최근 30일)
I have a file recorded with a RealSense-camera and it is saved as a rosbag file .bag.
I want to access the individual frames as images through Matlab and I have found information how to do from different forums. One example is from Matlab answers:
The problem is that that the function readImage doesn't work.
Depending on how I use it I get different error messages.
Array indices must be positive integers or logical values.
The error is generated with this code:
bag = rosbag('20190402_093734.bag');
bagInfo = rosbag('info', '20190402_093734.bag')
bSel = select(bag, 'Topic', '/device_0/sensor_1/Color_0/image/data');
msgs = readMessages(bSel,"DataFormat","struct");
img = readImage(msgs{1});
Undefined function or variable 'readImage'.
The error is generated with this code:
bag = rosbag('20190402_093734.bag');
bagselect1 = select(bag, 'Topic', '/device_0/sensor_0/Depth_0/image/data')
bagselect2 = select(bag, 'Time', [1 5], 'Topic', '/device_0/sensor_0/Depth_0/image/data')
bagselect3 = select(bagselect2, 'Time', [1 5])
msgs = readMessages(bagselect3,"DataFormat","struct");
img = readImage(msgs{1});
I thought there was a problem with my installation of ROS so I tried using the online version of MATLAB but I got the same error message there.
I am assuming that there is a very simple, logical solution to this but I have no idea of what it might be. Could it be a problem with the .ros-file?

  댓글 수: 0

Sign in to comment.

채택된 답변

Cam Salzberger
Cam Salzberger 11 Apr 2019
Hello Ulrik,
It's good that you are experimenting with the 'DataFormat','struct' option for extracting messages from rosbags, since it is a big performance improvement. Unfortunately, the convenience functions (readImage, readPointCloud, etc.) don't yet support accepting structs as input, and are expecting ROS message objects. If you want to use readImage, I would suggest leaving off the 'DataFormat','struct' option, and passing the output to readImage. Otherwise, you can manually extract the image from the ROS message structure.

  댓글 수: 5

표시 이전 댓글 수: 2
Ulrik Söderström
Ulrik Söderström 16 Apr 2019
Hi Cam.
Thanks a lot :).
When I create an empty message and copy all the content (except Header) I can use readImage perfectly.
Mohamed Atia
Mohamed Atia 27 Dec 2019
Could you please post the code that you used to "create an empty message and copy all the content (except Header) " so you can use readImage ? Thanks
Cam Salzberger
Cam Salzberger 2 Jan 2020
Something like this should work, though I haven't tested it:
msgStructs = readMessages(bagSel, 'DataFormat', 'struct');
msg = copyImage(msgStructs{1});
I = readImage(msg);
function msg = copyImage(msgStruct)
msg = rosmessage(msgStruct.MessageType);
fNames = fieldnames(msg);
for k = 1:numel(fNames)
if ~any(strcmp(fNames{k}, {'MessageType', 'Header'}))
msg.(fNames{k}) = msgStruct.(fNames{k});

Sign in to comment.

추가 답변(0개)





Translated by