sun shadow question

I'm new to grasshopper... I'm working with a group of regular buildings and want to find a way to view the supposed shadows of these buildings created by the sun during certain hours of the afternoon. Is this possible?

Attachments:

Picture 11.png, 301 KB

Replies to This Discussion

Permalink Reply by Chris Tietjen on July 10, 2011 at 7:14pm

The basic components you need are in the Mesh>Util dropdown menu.

Chris

Permalink Reply by David Rutten on July 11, 2011 at 3:49am

This will only cast shadows onto flat planes though. It seems Caroline has a freeform ground. One possible way forward from Chris' solution would be to create an extrusion of the shadow outline, then intersect this extrusion (Mesh|Mesh intersection probably makes the most sense) with the ground shape.

It sounds somewhat tricky but probably do-able. Unfortunately I've broken the file-format in the internal release so any files I creates you won't be able to open.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by David Rutten on July 11, 2011 at 4:02am

Nah forget that. The Rhino MeshMesh intersector just can't handle this. Which is odd since it doesn't seem like a difficult problem.

You also have to make absolutely sure that none of the buildings poke out the bottom of the landscape shape, or they'll cast 'reverse shadows' in front of them.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by David Rutten on July 11, 2011 at 4:25am

Ok, good news after all. The Rhino SDK offers two different MeshMesh intersection algorithms. The Mesh intersector component uses something called MeshMeshAccurate(). If you use the other one (called MeshMeshFast) you get the correct result. Albeit as a collection of loose line segments instead of closed curves. But you just have to use an extra Curve Join component to perform the last step.

You'll need to create a VB Script component and set the x and y input type hint to Mesh. Then add the following code:

A = Intersect.Intersection.MeshMeshFast(x, y)

This seems to give correct results in my test case.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by David Rutten on July 11, 2011 at 4:37am

I added both algorithms to the Mesh|Mesh component, with an option in the component menu to toggle between them. The default is off (so that the component works the same as before).

The difference between both algorithms is

MeshMeshAccurate:

MeshMeshFast:

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by David Rutten on July 11, 2011 at 4:41am

Oh, and MeshMeshFast including a massive Curve Join operation takes 17ms on the above example whereas MeshMeshAccurate takes 220ms. More than 12 times as fast.

I think I might switch on the Alternative Algorithm by default after all.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by taz on July 11, 2011 at 1:39pm

Can you add an info flag somewhere to alert users that this particular intersection routine has an alternate algorithm option?

I know I'm going to forget by the time I need to use it...

Permalink Reply by David Rutten on July 11, 2011 at 2:01pm

It's on by default. I could make this an import option instead of a hard-to-find menu item. Would that be any better?

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by taz on July 11, 2011 at 2:14pm

I guess that's what I was thinking if adding another input doesn't irk your component consistency standards (for the 10% of the time it might matter).

Permalink Reply by Volha on July 13, 2012 at 4:49am

Hi David and team,

I am wondering if someone can give me a few tips on how to handle curves after MeshMesh intersection. I am trying to contour casted shadows. It works fine on flat planes as you can see on attached jpg. David’s method of casting shadows on flat planes using MeshMesh intersection also worked. The problem is that I can’t contour my shadows any more. Any idea how can I find a contour normal to each shadow?

Thanks.

Permalink Reply by Danny Boyes on July 13, 2012 at 5:08am

Hi Volha

If you upload your files to I can look into for you.

Permalink Reply by Volha on July 14, 2012 at 12:42am

Hi Danny,

Thank you for your response. Please disregard my question. I was able to figure it out on my own. I simply projected my shadow lines from a flat plane to a free form surface. It worked.