Trying to display sensor_msgs/Image in rqt_bag

asked 2018-04-30 13:25:18 -0600

alejandro
3 ●2 ●2 ●5

updated 2018-04-30 13:33:22 -0600

I´m trying to display a custom message in rqt_bag. For that, I´ve tried the following:

msg = Image() //This is the initialization of my message
msg.image = self.msg
self.bag.write(topic, msg, self.msg.header.stamp)
self.bag2.write(topic, self.msg, self.msg.header.stamp)

My message content (msg) is just: sensor_msgs/Image image.
rqt_bag message (self.msg) contents:
std_msgs/Header header
uint32 height
uint32 width
string encoding
uint8 is_bigendian
uint32 step
uint8[] data
self.msg is tyoe sensor_msgs/Image, that´s why I can save the whole self.msg into msg.image

If I try to open the bag2 file which the one that uses the msg that rqt_bag creates, all works. However, If i try to open my custom message, rqt_bag doesn´t allow me to display the images.

I´ve also tried to save each field from self.msg to msg making first my custom message (msg) have the same structure as the rqt_bag message (self.msg):

msg.header = self.msg.header
msg.height = self.msg.height...
(in bag)-----------(in bag2)

Doing this what I have realized is that bag weights 306kB and bag2 308kB. It is like if there is some extra date somewhere which I don´t know.

Neither ways work for me. What can I do so that rqt_bag displays the images save on my custom message?? Thank you.

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Comments

This may be slightly off point, but why are you trying to use a custom message to do exactly the same job as sensor_msgs/Image?

PeteBlackerThe3rd ( 2018-04-30 17:38:32 -0600 )edit

@PeteBlackerThe3rd cause I need to add extra parameters but I prefer to go little by little.

alejandro ( 2018-04-30 17:45:02 -0600 )edit

There is a much easier way of doing this, you can nest message types. Create your custom message type which includes a sensor_msgs/Image message along with the extra parameters you want to add. No need to re-invent the wheel.

PeteBlackerThe3rd ( 2018-04-30 17:48:45 -0600 )edit

@PeteBlackerThe3rd I dont know exactly what u mean. What I want is a message with sensor_msgs/Image image, string name, int8 number. Then, I have to store that msg in a bag, and finally display that bag in rqt_bag but i cant. Any idea? What u were saying is valid for this? If it is, can u explain?

alejandro ( 2018-05-01 09:37:07 -0600 )edit

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answered 2018-05-01 12:55:30 -0600

PeteBlackerThe3rd

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Replying to your question and subsequent comments: A custom message type which includes a sensor_msgs/image field will do everything you ask for apart from being visible in rqt_bag. An example .msg file for this would be

# my custom message type
# embedded image message
sensor_msgs/image myImage
# the extra fields needed
string name
int8 number

rqt_bag will only display sensor_msgs/image messages as images, it will not show any custom message types unless you make a plugin to extend its functionality. This is also true if you make a custom message type that has the same structure as sensor_msgs/image ROS still considers that a different type of message.

If you really need to view these images in rqt_bag then you could publish a normal sensor_msgs/image message at the same time as your custom message. This way you could view them in rqt_bag and use the custom message in the other nodes that use that information.

Comments

You are talking about publish messages but I don´t pretend to publish messages like in some examples of Publisher-Subscriber. I only want to save that msg in a bag file and then display that bag with rqt_bag. Reading what you say, it seems to be impossible unless I change rqt_bag code?

alejandro ( 2018-05-01 13:06:42 -0600 )edit

What is the actual problem you are Trying to solve? Saving messages in bag files and viewing images in rqt_bag is an unusual use of the ROS system.

PeteBlackerThe3rd ( 2018-05-01 13:28:05 -0600 )edit

The problem is not saving the message but displaying that custom message which contains as I said before a sensor_msgs/Image and other parameters like strings. Rqt_bag doesn´t allow me to view (by type or topic) those images.

alejandro ( 2018-05-01 17:28:14 -0600 )edit

Rqt_bag doesn't have this feature unless you add it with a custom plugin. My comment about publishing two messages is just as valid for saving two messages to a bag file, the concept is the same.

PeteBlackerThe3rd ( 2018-05-02 02:37:10 -0600 )edit

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Trying to display sensor_msgs/Image in rqt_bag

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