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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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  • $\begingroup$ One program is (not free...) : archiexpo.com/prod/ades/product-125833-1414289.html $\endgroup$ – Solar Mike Jan 31 '18 at 21:51
  • $\begingroup$ Are you looking for a theoretical answer of how to do this or for a software recommendation? $\endgroup$ – Wasabi Jan 31 '18 at 21:58
  • $\begingroup$ If you are looking for software recommendation, the following can be used (but not free): 1. Lumion 2. Vray (with SketchUp) 3. LumenRT $\endgroup$ – Jem Eripol Feb 1 '18 at 0:07
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Autodesk 3D Studio used to do this when I was rendering with it around years 2000 to 2005. It is not free though.

you could define one or many light sources and one or several cameras and then animate your model around a path and it would calculate the shadows and reflections and even you could define opacity, translucency, surface mesh any building material.

I have no doubt that it is more capable now and has many more features! But they may call it a different name now.

As for the tracing of your earth orbit and daytime and sun angles there are many formulas that can be easily manipulated to be able to use them as input for the light source path, or you can get the stepwise coordinates in 'MS Excel' and plot them.

How ever for a task as simple as what you need you can approximate you angles by 4 intervals a day and four seasons!

Because the design can not be sensitive to any level of change more than that!

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  • $\begingroup$ @GlenH7 only trying to be helpful... $\endgroup$ – Solar Mike Feb 1 '18 at 13:20
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All raytracers can do these, any system supporting depthmaps can do these. Most systems 3D can even do it analytically for each timestep. Many 3D applications have a dedicated sky simulation pakage so no need to even calculate the sun path jus give coordinates and time. They will even gladly simulate the contribution of ambient sky if you want (even heat loss/input).

So wether you use 3DS max, Maya, Sketchup, Rhino or blender matters little. Hell even most CAD packages meant for mechanical engineering can do this without any problems.

Since you want free use blender, using something like this. Though to be honest even your browser is capable of doing this.

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