Help with back plates and EXR

[Bosseye]

Ok, bit of a n00b question and sorry if this is buried somewhere on the forum, I did search but I can't find a specific answer.

I'm trying to understand how to go about using back plates combined with an EXR file in Sketchup. I've been using EXR files for ages but only generally for lighting and reflections. If I try to use them as a background they always look wrong as they're too zoomed in and a bit low res looking (even if they massively high res files).

What I can't seem to find out is how to use back plates correctly - for example see below, every render you see of a car on a road, the car looks like its actually on the road with all the correct lighting etc - how is this done? How is the car made to look like its actually on the surface, when I'm assuming its a back plate image? See the images attached for what I mean.

So I've got the free sample from here http://www.hdri-locations.com/ which comes with all the backplates and the HDR file (which I have converted to an EXR file). Can anyone give me a simple walkthrough on how to use them both effectively?

Thanks

[Bosseye]

Ok so I've been fiddling around and come up with one way to do it, but its a bit rubbish:

So I've made an open box in Sketchup as the ground and sides and plonked my car model in it (its a good car model for Sketchup, but isn't a great model I know, its just for testing).

Then I've used the 'match new photo' feature in Sketchup to plonk a back plate in, then moved and tweaked the view until the car looks vaguely correct in the background context. I've set the matching EXR as the environment background, then I've projected the photo onto the geometry, exploded the distorted textures under UV mapping and voila:

The model

Rendered looks like this:

Which is an approximation of the proper versions, but some problems;

- Projecting and exploding distorted textures has a tendency to blur them slightly. Is there a way around this?
- The back plate is slightly low res, presumably this is down to it being a down scaled sample file?
- Projecting textures onto geometry in Sketchup results in obvious joins, see along the back and up in the top right corner. It also ever so slightly alters the colours/contrast between the textures so each face texture is subtly different from its neighbour. Is there a way around this?

Is there a more intelligent way to do this sort of render?

Thanks,