# How do I create a cast shadow for this object?

I have recently begun learning how to cast shadows with isometric objects, but I feel like I am missing something in the case of the object below

At first I simply believed that I could follow the same general process as with a simple cube, but that resulted in this first attempt.

As you can see, I have found some of the intersecting points of the shadow, but I am having trouble determining where to place the rest of the construction lines to perfectly cast the rest of it. If anyone could tell me exactly what I am not understanding and provide an example of a cast shadow in this particular case, then I would greatly appreciate it.

Edit:

Thanks to everyone's help I was able to cast a shadow on this object. Here provided below is an image of my solution with the minimum number of construction lines used to cast the shadow.

• your doing it almost right its just that your neglecting half of the shadowcaster. so the second red line from top should have been cast from the opposite corner. read the near duplicate graphicdesign.stackexchange.com/questions/86697/… Mar 22 at 16:20

In the next image a ray of light (=red) comes from the infinity via one corner (=A) of the 3D shape. I assume all light comes from a single infinitely distant source.

The drawn ray can actually be anywhere in the plane which looks a line in the used view, so it's an open thing where the ray meets the ground. You can decide it freely as long as you do not change the direction of the ray in the drawing. It's useful to let that point be on the grid because it maximizes the usability of the grid in drawing the shadow. For that reason in the next image the ray is shortened to a point on the grid.

Corner Ag of the 3D shape is the ground projection of A. The green L is drawn to be used as a jig to find the places of all shadow corners of shape corners which have the same elevation of A.

A copy of the shadow corner jig is used to draw the grey shadow in the next image.

It's not the whole shadow of the vertical bar, it covers only one rectangular face. You must construct the shadow for the whole 3D shape piece by piece and make an union.

In the next image the light ray and the green L is used to make the equivalent shadow corner placement jig for a lower elevation corner B

The line from the ground projection point Bg to the right ending of the ray (C) has the same direction as the ground branch of the green L. In the next image the ready to use corner shadow placement jig for the elevation of B is drawn as magenta

"Spares" is a collection of duplicates for speed. The grey 4-gon is converted to path. It's easy to drag the corners of a 4-gon with the node tool to the places found with the jigs.

Every face of the 3D shape must be at least checked if it needs a shadow. In the next image one of them is made:

It was easy to say what to do, but in practice you can succeed only by working systematically. Divide the surface of the 3D shape to rectangular faces and draw their shadows one by one. Do not forget vertical faces! Mark somehow which face is already handled.

Send ready partial shadows to back and move the jigs to the corners of the next face. You hopefully learn to see which faces do not actually need own partial shadow because they cannot get any light or the shadow is a part of the union of already drawn partial shadows.

As said above, one can leave out all no-light faces of the shape. As well one can make the partial shadows of all no-light faces and leave all illuminated faces out.

There's always some invisible faces which must be taken into the account. Fortunately they are easy to find in a isometric grid drawing. Drawing an unnecessary partial shadow doesn't harm.

This is the next partial shadow for a lower elevation face:

It's actually a no-light face, but drawing its shadow is not useless. Together with the already drawn top face shadow it makes drawing the shadow for the most distant invisible vertical face unnecessary.

And this is the final result for my simple 3D shape. The partial shadows are also shown as detached.

Actually one part is still missing - the shadow below the bottom face of the vertical bar. Fill the surface areas of the 3D shape to hide the invisible parts of the shadow.

• For this angle of shadow, you'll have to draw the shadows of some rectangles that aren't visible from the front. This is fine, but might take some thinking. Mar 22 at 16:26
• It is difficult to be systematic enough. But it's possible. In a 3D cad program everything is easier. Even the simplest program which has no light effects at all can create the right shadow if you extrude the surfaces along the ray and extract the ground plane corossing. This is the isometric view of my shape, ray and ground plane: i.stack.imgur.com/rOIiK.jpg and this is the shadow made by extruding all along the ray through the ground plane i.stack.imgur.com/yBEXz.jpg Mar 22 at 16:45
• Thank you so much for your very detailed answer! You have saved me a great deal of time and effort trying to understand this particular subject and it means the world to me. Mar 23 at 8:14

Without wanting to go into more textual details here a solution, with different shadow direction. (click to zoom)

• This was also a very good answer to my question, simple and straight to the point. Mar 25 at 0:46