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Imagine a house/building, seen from outside, at sunrise. As the the sun moves in the horizon, a) the shadow of the house is displaced/deformed, and b) some faces of the house have more/less sunlight in the afternoon than in the morning.

I need to predict those changes along the day and along the year. Besides the external 3D shape of the house, this only depends on space & time. Space: the latitude, longitude and orientation of the house/building. Time: the hour, day, month of interest.

I have the exterior measurements of the house. At this point I treat the house as a solid object (ie I don't care about the light inside the house; I also don't care about cases where light which passes thorough the building eg two opposite windows).

I only need to predict two interrelated things (along the day/year) for planning and visualization purposes:

1) the shadow of the house

2) the faces of the house which will be receiving light

With (1) I can predict how the adjacent buildings/parks/spaces would be affected by sunlight decrease and with (2) I can plan to put more/less and/or smaller/larger windows in different places of each wall of the house.

I know that many years ago this was possible with a plugin for Google Sketchup, but for different reasons I would like not to use this option but a free application (if FOSS, even better). Given the recent surge of 3D modeling/design programs I thought maybe there are other programs which are capable of doing this.

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    Do you have access to a high-resolution DEM of the area? – JoshC Jan 31 '18 at 17:59
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As JoshC mentioned in the comments, if you can make a DEM raster with the height of the house, you can then use several programs to check your shadows, as per this answer: Simulate sun movement One of the points in that answer is a GRASS plugin included in QGIS.

You could make a rough DEM raster yourself by picking some points in QGIS, giving them a height and then using Rasterize (Vector to raster).

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