I’ve played with Aravis for some time, and I had some questions about Feature nodes and their Access Mode.
When I start the acquisition of a camera, some features are still marked as writable when I check their actual Access Mode while it’s supposed to be read only.
For example, I expect the feature “Width” to be read only after I start the acquisition, but it’s writable. And when I write on it, the camera is in a weird state, where all my buffers status are ARV_BUFFER_STATUS_SIZE_MISMATCH.
I’ve tested this on a Basler camera (acA2500-14gc) and with a Fake camera.
I also tested this with a Daheng camera (MER-503-20GC-P) but I got a different result: Access Mode is still marked as writable, but when I try to write on it, it raises an exception.
Is this intended ? Is there another way to check the access mode of a feature node I’m not aware of ?
I’ve tried these scenarios with python bindings of aravis 0.8.13 and 0.8.21 and got the same results.
AccessMode is available in Aravis API, but is not enforced on read/write operations. Which means some cameras may be put in an incorrect state if a feature is written while it is read only. On other devices with a better implementation, an error message is returned, which generate an exception in Aravis (I guess you are using Python).
The reason AccessMode is not enforced in Aravis is it is still not considered completely reliable. It is better to always allow read/write feature access than forbid a legitimate access due to an incorrect AccessMode value.
Yes, I forgot to mention that I was using Python bindings, but I also tried the case with C code directly to make sure this wasn’t a problem from the bindings or python itself.
I understand the reasons now. What would be the reason of the lack of reliabiliy of this feature ? It isn’t supposed to follow the genicam standard ?
The main reason is nobody stepped up to improve its reliability. And also because testing the reliability means to be able to test Aravis on a lots of devices.
Hi,
Is this issue still unresolved?
I used the recent aravis for testing and found that some feature nodes that should be read-only are still writable in the acquisition state.
Or is there something wrong with the way I use it?
Yes,
When I call arv_camera_set_access_check_policy after creating the camera object using arv_camera_new to set the access check policy to enable.
Then start acquisition, and then use arv_gc_feature_node_get_actual_access_mode to return the result still RW.
Please open an issue on github, and attach there the genicam data, as well as the console output when you are running your code with ARV_DEBUG set to genicam:3