Shadow Analysis Roof Invisible

Hello, I know there are a couple of topics relating to this issue flying around the forum, but many are very old and links to files are not working. So I thought I would ask the question again.

I am trying and failing to generate a shadow study within an office layout that shows the solar gain from the perimeter glazing. I have taken the section plane to 1000mm from Level 01 FFl and now the light comes in from the top (Although the roof layer is switched on and the roof is visible when the section plane is not active.)

Any help would be great.


The section plane visually cuts away the roof geometry so naturally you’ll get light from above. Don’t use a section plane but a large face that has been textured with a transparent png (so not a jpg). and the roof on a layer turned off.

Or use a section plane to cut away the roof a large face that has been textured with a transparent png

The painted face lets you see through but it still casts shadow on the floor as if the roof is still there. Only light through the windows will be seen.

p.s. try it with a face painted with fencing chain link material.

added example image:

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Also, any material with transparency set to a lower value than 70% casts shadows.

true, … but makes it more difficult to see what is going on below the plane.

Does this still work ?
in older version of SU i successfully got transparent .png file onto face and hid edges, this cast a shadow. Now when i try it transparent .PNG appears orange.
Any changes to way materials work between SU 8 and 2018 ?

I’m on a chromebook with the SU web version right now and it stiil works for me.
It should also still work with SU2018.
Apply the transparent png as a texture to a face, not as an image.
If imported as an image, you’ll have to explode the image to get to its texture.

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Hi, I was trying with 1 pixel, maybe i should try larger image…

I’m not sure what the size needs to be but for sure not much more. It’s like applying a color, a few should be enough.

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If you have Thea renderer it respects the same internal lighting with or without a section plane. So you can see inside the space but the lighting remains the same as if the section cut opening wasn’t there. I’m not sure why Sketchup wouldn’t do the same. The inherent use of a section plane is to see within geometry but should not affect lighting?


still have problems with this one, Im still getting a transparent orange look no matter what colour i pick , with tranparent .png texture enabled.
anyone want to share transparent .png with me? (photoshop sometimes is telling me it cannot save image due to image being empty ) cheers

I hope this (above) works

added: the shared “invisible” png above works for me on a fresh model.
Note that you don’t have to explode the png image to texture. But then you need to look if the image is set to also cast shadow if you need it as sort of an invisible ceiling casting shadow below. And then you are limited to a (scaled) rectangular shape. Exploding to texture makes it easier to apply on other faces.

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thanks, ill give it a go

Hi wo3dan
Thanks for PNG
That seems to have done the trick !,
Not sure exactly what happened -but i think i implemented it through entity info rather than materials dialogue,
In entity info it seems that it is possible to have 2 materials per face, and this might be one reason couldn’t get it working before - i.e one face transparent whereas reverse side not ?,
anyhow, great to have this working !!, cheers

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Yes, that’s probably it.
Applying a transparent metarial to a face will be applied to front and back if both face sides were still default. Opposed to a non-transparent, which will only be applied to the side you paint it on.
(SketchUp seems to be clever here)
But you can always paint (later) each side a different texture.
If one side is transparent you can look through from its side, even though the other side may be painted differently with non-transparent texture, making it “view blocked” from that side.

Give your “one pixel” another try.
Or you could try to reduce my png’s length/width. You only need a verrrry small sample to paint faces with it.

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Here I just made a square in photoshop ( uncheck lock button) and made asmall pixel line selection and filled it with black, inverted and deleted everything else so its all transparent except for line. Save as a png.

in sketchhup this is applied as a texture a rectangular roof cover. You can then scale the png to be bigger than the roof size to get rid of the black line part. you can also shift+delete the edges.


Can’t the png consist of 100% transparent pixels? I’m confused, why have the line?

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Yes it could be 100% transparent, I think the idea of having some solid entity in there was to make it obvious/tangible that which was transparent, but you are right in that it could be a blank .png image (non-image).