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Can anyone think of a simple way to create a polygon to represent building shadows?

I have a shapefile with height information for the buildings and I want to create a simple plan looking like the image below:

dropped shadows

I don't want it to be accurate based on the terrain etc or really specific of the sun, but just a way to demonstrate the height of the building with a shadow that is connected to the building.

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  • You need can use the 2.5 D render where you use your height column as a data defined input
    – kartoza-geek
    May 28, 2019 at 16:18
  • here is a short video on the 2.5D Render as mentioned by @kartoza-geek vimeo.com/149742884
    – Mapperz ♦
    May 28, 2019 at 16:23
  • Yes, I'll try to get an answer written up using a Geometry Generator that uses the translate(geom,dx,dy) function. It should be able to get the delta x and delta y values from your height field and maybe even using a scale() function. Currently away from desk so will try to get it up in a bit here if someone doesn't beat me to it.
    – SaultDon
    May 28, 2019 at 16:27

3 Answers 3

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Use Translate, in the toolbox:

Translate

here I set dx and dy both to .71*Height to simulate a 45° sun incidence, but you can use whatever combination you prefer.

This creates a new layer, which you have to move under your original one, and set to a dark shade. Optionally, for a smoother rendering, set a slight blur with the Draw effect:

add-a-blur

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  • Thant's great! thank you! Any ideas on how to connect the corner of the shadows to the corner of the buildings?
    – George
    May 28, 2019 at 17:30
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    Where did the .71 come from and how is this used to simulate the sun angle?
    – user35594
    Oct 19, 2020 at 15:03
  • .71 is an approximation of cos(45°) , where 45° is the incidence angle of the sun light that I wanted to simulate. At noon the sun may be for example 70° (depending on day of the year and your latitude), so you could use cos(70°) = 0.34 and shadows will be correspondingly shorter.
    – RafDouglas C. Tommasi
    Oct 20, 2020 at 11:14
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You can use also the Draw effects and select Drop Shadow option. Using this option does not require to create a new file with modified geometry. Drop Shadow option gives you the ability to change the Blur and the direction of shadow freely and easily without the need to create a new file each time.

  • Go the buildings polygon's Layer properties -> Symbology -> select Simple fill -> Draw Effects

enter image description here

  • Click on the Yellow star
  • Select the Drop shadow option and select it to see its options

enter image description here

Here is a sample building before and after using Draw effects:

Before:

enter image description here

After:

enter image description here

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    This is a good and fast approach, however it does not take into account the actual building height, i.e. all shadows are offset by the same distance. For a quick visual effect however it is a good compromise. :)
    – RafDouglas C. Tommasi
    May 29, 2019 at 6:15
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This is an old thread but in case anyone is looking for how to set this up using the 2.5 D symbology mentioned in the comments here it is:

25D Setup

The key is to generate a negative height. In this case I am multiplying my stories field by -10. Make sure to turn off shade walls based on aspect and shadow.

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