Good RPC Tree Shadows (Without Projector Maps)

[tmccarter]

Hey all,

 

This forum and its members have been very good to me, so I'm going to give back. Here's a little trick I discovered for getting RPC trees to cast good shadows (without using projector maps).

 

As you may know, when your shadow-casting light source approaches a 90-degree angle to the camera's point of view, your RPC trees cast really thin shadows (see first attached image). ArchVision recommends setting up a projector map to get a better shadow, but this technique isn't compatible with VRayLights, and your shadows aren't very realistic at times. I discovered a way to use an opacity-mapped plane that casts a perfect shadow, but is invisible at render time.

 

Here's the trick:

1. In the front or side viewport, Draw a vertical plane that is the same height and width as your RPC tree and place it in the same position as the tree.
   
2. Rotate the plane so that it faces directly towards your shadow-casting light source.
   • This will ensure that your plane casts a clean, undistorted shadow.

[*]Make a new material for the plane. (I'll use VrayMtl in my example.)

[*]In the material settings for your new plane material, set diffuse color to black. Leave reflection and refraction at none (black). Make sure 2-sided is enabled.

[*]In the maps rollout, make sure Opacity is set to 100, and then plug in a bitmap for the opacity map.

• This image will define what your shadow looks like, so you'll want to choose a pure black image with white defining the shape of your tree.
  
• RPC trees come with shadow map images, which are alpha channel images taken at 45 degrees and overhead. These work great for this trick. Choose the one that matches your RPC tree.

[*]Apply the material to the plane, and click the icon to show in viewport.

[*](This is the important one) With the tree shadow plane selected, right click in the viewport and select "Properties", bringing up the Object Properties dialog. UNCHECK the checkbox that says: "Visible to Camera" and make sure the checkboxes in front of "Visible to Reflection/Refraction" and "Cast Shadows" are checked.

[*]Select your RPC tree and in the RPC parameters rollout, make sure "Cast Shadows" is unchecked. This turns off the default rpc shadow to ensure you get one clean shadow.

[*]Render your scene. You should see your RPC casting a perfect shadow, no matter what relative angle the camera and light source are at. (See second attachment.) If you move your sun, just rotate the shadow plane to face it and you'll always get a perfect shadow.

You could also use this technique to cast a good noontime shadow by drawing a horizontal plane (drawn from top viewport) and using an overhead picture as your opacity map (which also come with RPC trees)

 

Enjoy!

 

-Tim McCarter