I am trying to render a layer of Rain with alpha to composite with a train animation. I have done this before successfully with volumetrics, but it isn't working now and I cannot figure out why.
Here is the montage of screen grabs. Sorry the rain is not clearer, it is affected by the depth of field of the camera but it helps to demonstrate that the train carriages are not blocking out the rain in the distance. I have used the "hold out" option in collections, which didn't work, so I also went through every single material for the mesh and switched out to a hold out node. Which also didn't work.
I thought it might be because I had some translucency with rain droplets affecting alpha compositing (though I don't know why it should) but that made no difference. What I should see is a field of rain blocked out by the train save for a few close up rain drops. But the train is not blocking or masking out the rain as it should. Does anyone have any ideas what the problem might be?
