Cycles bake to a flat surface / plane

Question

I try baking foliage to a flat surface as seen in a 3D Max tutorial.

However, parts are just missing on the bake.

Is it even possible to bake geometry to a flat surface? I tried all options, like a cage, moving the bake target around (in front of the object, behind, in centre) etc.

I need to bake because I need other channels too, like normals, AO etc. Otherwise I could just render it.

UPDATE: I think I got closer to the actual problem - see 3rd image please. Its the normals facing the camera directly, become black. That may not even be an error, still I don't really know how to compensate for that.

ANOTHER UPDATE: After doing some research I found out that the black parts in the 3rd image are indeed no error - Normals go on the red, green and blue channel from -1 to 1. On a regular image values below 0 are displayed as black. Still I don't have no clue why those values are just cut-out of all baked maps - a normal bake should contain the negative values and it should work correctly when used as normal map. Furthermore a diffuse bake shouldn't be affected at all.

I guess this is a bug - and a waist of a day.

Bake result

Actual geometry (full render)

Render with normal emission material

Another bake attempt following fergal's instructions

Answer 1

Okay so I've prepared this blend file: http://www.pasteall.org/blend/40069

It's a crude attempt at recreating your scene, but essentially, we have a large plane (which we want to bake our geometry to), and a number of smaller planes (which represents the geometry you want to bake)

Open the file. Select the large plane, tab into edit mode, select all vertices, press U, and then select "Unwrap"

Right click on the edge of the 3D viewport, select "Split area", and in the new area that appears, switch to the UV image editor. In the UV image editor, select "New" from the toolbar along the bottom, and create a new image:

Next, in the materials tab, create a new material, and under the "Surface" panel, click the little dot to the right of the "Color" widget, and select "Image Texture":

Click the dropdown to the left of the "Open" button, and select the image that you created in the UV image editor. Next, tab out of edit mode, and back into object mode. In the 3D viewport, select all the smaller planes, and then select the large plane. Make sure you select the large plane last, as this will make it the active object in the scene (indicated by the brighter shader of orange):

Next, under the Render tab, scroll down to the Bake panel, change the Bake type to "Diffuse Color", check "Selected to Active", and set the margin to 0px, and click "Bake":

Now, in the UV image editor pane, you should see the geometry of your scene baked onto the texture. However, you will notice that only some of the geometry has been baked to the plane, which I think is what's happening in your first screenshot. To capture the remaining geometry, increase the "Ray Distance" value under the "Bake" panel (it's located just under the "Selected to Active" checkbox). In my example, I have set "Ray Distance" to 3. Now, click "Bake" again, and this time, all geometry will be captured in the bake:

Does that solve your problem?

Answer 2

Found the solution after hours, at least partially.

• Bake as usual (resp. as described by fergal), have "Clear" active on the bake tab. Only half of the objects will be baked onto the image
• Now deselect "Clear"
• Go to your target plane in edit mode, select face(s) and hit ctrl+f -> flip normals
• Bake again, without the clearing the bake will now add the other half onto the image

One problem remains: Doing it that way will bake one half of the normals technically in the wrong direction, the half that should be on the normal map as negative values. No clue, how this is actually supposed to work.