ximea xiAPI device id can't be trusted

[carandraug]

After creating the Camera object, if the camera is opened by anything other than device id, then the device id will be incorrect. This means that all other Camera methods that use the device id will be acting on another camera.

The problem of using device id to initialize cameras is that in a muti camera setup we don't know which id each camera has. So serial numbers is used instead.

Example:

# Two cameras get initialized by serial number so both return the same
# default id of zero (which is not updated after opening the camera).
# Reading device information then always returns information for the
# camera with device ID zero.
>>> from ximea import xiapi
>>> c1 = xiapi.Camera()
>>> c2 = xiapi.Camera()
>>> print('c1 device ID = %d; c2 device ID = %d'
...       % (c1.dev_id, c2.dev_id))
c1 device ID = 0; c2 device ID = 0
>>> c1.open_device_by_SN('00982350')
xiAPI: ---- xiOpenDeviceBy API:V4.19.11.00 started ----
[....]
xiAPI: ---- Device opened. Model:MQ042MG-CM SN:00982350 FwF1: API:V4.19.11.00 ----
>>> c2.open_device_by_SN('38880050')
xiAPI: ---- xiOpenDeviceBy API:V4.19.11.00 started ----
[...]
xiAPI: ---- Device opened. Model:MQ042MG-CM SN:38880050 FwF1: API:V4.19.11.00 ----
>>> print('c1 device ID = %d; c2 device ID = %d'
...       % (c1.dev_id, c2.dev_id))
c1 device ID = 0; c2 device ID = 0
>>> print('c1 device SN = %s; c1 device SN = %s'
...       % (c1.get_device_info_string('device_sn'),
...          c2.get_device_info_string('device_sn')))
c1 device SN = b'00982350'; c1 device SN = b'00982350'

[carandraug]

This has been reported to ximea and is ticket 55457 on ximea's ticket system (which unfortunately is private).

[carandraug]

The value of the dev_id property is actually called enumeration ID by Ximea support. For them, device ID is the unique ID of the chip of the camera which is used internally. The XiAPI also calls it index ID.

Anyway, my conclusion is that it's better to just ignore Camera.dev_id and be careful of Camera.get_device_info_string. The enumeration ID (dev_id) of a camera is not guaranteed during one session, and might change each time get_number_devices() is called. Also, because get_device_info_string() internally uses dev_id, it should only be called when we know that dev_id has been set correctly.