r2L4096 cannot be initialised due to missing OffsetY

[PranglB]

Describe the bug
When connecting an r2L4096-29gm some parameter is not found:
ERROR: from element /GstPipeline:pipeline0/GstPylonSrc:pylonsrc0: Failed to get caps.
Additional debug info:
../ext/pylon/gstpylonsrc.cpp(584): gst_pylon_src_get_caps (): /GstPipeline:pipeline0/GstPylonSrc:pylonsrc0:
Parameter not found in CIntegerParameter::GetValue. (No node attached.)
ERROR: pipeline doesn't want to preroll.

To Reproduce
gst-launch-1.0 pylonsrc device-serial-number=40635748 num-buffers=1 ! videoconvert ! pngenc ! filesink location=frame.png

Expected behavior
Saving one image

Environment

• Camera: r2L4096-29gm
• Nvidia Jetson Jetpack 5.1.2-b104

version
Description Basler/Pylon plugin for pylon SDK 8.0.0(10)
Version 1.0.0-9-g625d3bb

Was solved by changing gstpylon.cpp [746] with the following:

gint64 orig_offset_y = 0;
if (self->camera->OffsetY.IsValid()){
orig_offset_y = self->camera->OffsetY.GetValue();
}

[bilannnn]

We ran into the same issue with a Basler Racer 2 (r2L4096-42g5c) in SingleLine acquisition mode. The root cause is in gst_pylon_query_caps in gstpylon.cpp — OffsetY.GetValue() is called unconditionally, but linescan cameras don't have OffsetY in their nodemap, which throws the exception.

We fixed it with:

gint64 orig_offset_y = 0;
if (self->camera->OffsetY.IsReadable()) {
  orig_offset_y = self->camera->OffsetY.GetValue();
}

We chose IsReadable() over IsValid() (which appears in some workarounds for this issue) because IsReadable() is the correct precondition for GetValue() per the Basler SDK guidelines — it checks both that the node exists and that it is accessible in the current camera state. IsValid() only checks node existence, so it could still return true for a node that is temporarily not readable.

The TrySetToMinimum() and TrySetValue() calls that follow were already safe since they use the Try variants.