Shadowcatcher Issue

[dj_buckley]

First problem - when I choose 'For Compositing' as the Alpha Mode - why does my ShadowCatcher object not render black?

Second problem, is there any way to exlude things to avoid doubling up of shadows etc?

I've attached a backplate I need to composite into.  I basically need to place a car in the shaded area of the road, and a car into the sunlit area of the road.

I've modelled the road, and I'm projecting the backplate onto it using the shadowcatcher material (is this correct).

I setup lighting using a simple sun/sky system to emulate the conditions in the backplate.

I've modelled the building that's casting the shadow across the road as I need to get that same shadow on the car and the reflections from it (this is the problem shadow - I don't want this shadow on the shadow catcher, just on the car, because well it's already on the backplate).

Is this possible?  Where am I going wrong?

[sprayer]

You can exclude shadowcathcer plane from light source and it won't catch drop shadow, but on sun light it wont' cast drop shadow so i think you may need second shadowcatcher object to cast shadows on the sun
https://i.imgur.com/UeL6QQj.jpg

[dj_buckley]

Makes sense, I can literally just split the current object down the shadow line and have the two separate objects.

[dj_buckley]

Ok so splitting the geometry down the shadow line and excluding half from the sun does exactly what I need.

The next issue is why my geometry isn't overridden as black when I choose 'For Compositing'

[mferster]

Are you talking about your cars or the ground? If you want the ground to be black in 'for compositing' mode, then remove your background image and change the environ/backplate color to black.

*Edit.
ORRRR put your environment shadowcatcher map into a rayswitch map with your img in all the slots except for direct visibility which would be black, and end up like the results below.

[dj_buckley]

The ground - I really just want the cars/shadows.

I hadn't removed the backplate from the shadowcatcher material.  That does the trick.

Thanks