(I have updated this thread to suit the latest release of Vray - to avoid confusing people with references to ‘linked materials’ etc which is now redundant - David)
HDR skies are ok but are unlikely to be specific to your site.
Site photos are ok, but are not hdr, so difficult to get them to ‘emit’ in the sky area and not ‘emit’ in the non-sky area, so they are less than perfect backgrounds.
SOLUTION
On location, take photo at 180deg to the intended photomatch view (or take several and stitch together) - image 1
Make an alpha map of the sky - image 2 - note this alpha map is inverted - so check the ‘invert’ box when inserting the map in the transparency slot.
In sketchup, set up billboards opposite the model to provide reflections - that is IMPORT image (‘use as image’) - then explode. You will now see the image appear in both the SU material editor and the Vray materail list. (set horizon of images to match model) - image 3
set transparency of billboard image to 100%
create vray linked material of image,
If you want the billboard to be emissive (it may otherwise be poorly lit and dull if the sun is behind it)
then put ( image 1) in a new emissive layer (at say an intensity of 3 for physical camera)
put alpha map in transparency slot of the same emissive layer
Use your ‘favourite’ hdr sky (or just the vray sky)
RENDER
This allows the sky to be bright and the non-sky areas to just act as skyline as this final image shows, but I realise this might be a sledgehammer to crack a nut(!).
Hope this is helpful
David
Image 1 - site photo
Image 2 - make alpha map
Image 3 - sketchup set-up
Image 4 RESULT
Image 5 Orginal photomatch image
Just to round it off - the background will cast a shadow, but only the non-sky area, so you don’t get the usual rectangular shadow that you often get with a regular billboard. This means you can sometimes use the shadows to your advantage. (I’ve put a plane in front of the billboard here, just to show the shadow result ;D
David, that is a very godo trick. very creative!!! : )
but one question, in your trick, you cant put the camera behind the billboard. rite? somehow even i set the transparency to 100%. the image still show up as emissive material. So if i put the camera behind the billboard, it will block my camera.
it’s because in the newer version, the material get linked automaticly. (In the past you had to link the sketchup material manually). So don’t worry about it
thanks for getting back to me, this is driving me insane!
ok so this is what i did,
make rectangle in sketchup opposite my model.
make a new vray material.
add image 1 into the diffuse layer (this is just a normal image of the site with sky included) is this where i am going wrong??
made a new emissive layer
put image one into an emissive layer
put the alphamap into the transparency of the emissive layer.
apply that material to the rectangle
this should then form the shadows like in DCAULDWELL’s final image. but it doesnt and i dont know where i am going wrong?
any technique for creating alpha maps of complex shapes like those trees?
Yes - its really easy.
Using your editor (Photoshop etc) make a copy of the original image, then make it greyscale and adjust the contrast until you get just B & W. You may want to ‘paint’ in more white to ensure the opacity - but that may not be necessary.
billboards seem to be the only possible way to work at VRAY for Sketchup.
Photoshop seems nice at first glance but the reflections are a problem.
Of course, in theory, you could add a bitmap as reflection in the options panel, but I get NOTHING out of it! I only get a reflection map if I set the bitmap as ENVIRONMENT SPHERICAL… but then, if I wanted my reflections to be so distorted, wouldnt it be easier to set the BACKGROUND ITSELF as ENVIROMENTAL SPHERICAL and use the same bitmap?
I realise that my post may be a bit confusing because it was written some time ago for an older version of Vray - I’ve now updated it and I hope it is clearer.