I’m imaging herbarium specimens that need to be displayed in portrait orientation. However even after correcting the orientation in lightroom the orientations are not correct after export. Do I need to set the orientation on the camera itself (Nikon D5600) or is there a Darktable solution?
How did you hold your camera when you took the picture?
Normally, the camera stores this information in the exif metadata and darktable respects that. However, you may have to switch on that option in the camera’s system menu. Mine is set to German, so I can only guess that it is called something like “Automatic picture orientation” in English.
The camera is on a mount facing downwards into a lightbox. So I don’t think its getting consistent detections of camera orientation.
Then maybe you should switch that option off on the camera (as suggested by the manual for such cases).
You can use the crop & rotate module in darktable’s darkroom to turn the picture the way you want. According to the manual, using selected image and then rotation in the lighttable view should also store the rotation as a history stack item that is processed upon export (darktable 3.6 user manual - selected images).
As a bulk solution I’d try using exiftool to directly override the orientation metadata 
That said I’ve never done it myself.
Thanks. I’m still working through various options and will try that.
Turning off the automatic rotation on the camera (Nikon D5600) on the mount puts all the images into landscape orientation. Previously the orientation was not consistent. I can rotate the pictures automatically into the desired portrait orientation using the Darktable image-processing style but this change is only retained if I export as jpegs, not NEF (i.e. RAW). Does anyone know how to get Darktable to retain the changed orientation when exporting NEF’s?
exporting RAW files in dt?
I just realised that RAW files can’t be changed. Checked with the project supervisor, now saying we must export as TIFF’s and JPEGs. That makes much more sense.