How to make a light source that lets my model cast a shadow

Gunter

I reconstructed the digital sundial from www.mojoptix.com in Onshape but since it will take upwards of 20 hours to 3D-print I need to test it first.  My model is here:

https://cad.onshape.com/documents/635c068aa276eb28ebb784f0/w/67d017e7f1c2ed4cb4172089/e/f9a6f620d73c3292c7b2dd9c

Testing means shining a far-away light on it and checking the light/shadow pattern of dot matrix numbers resulting below the gnomon.

I tried suspending a large rectangle above the gnomon and extruding it, but of course the extrusion flows around obstructions - o good.  Extruding up to next and up to part failed.

I tried the ray tracer featurescript but it has no check box for simply blocking, i.e. absorbing light.  Possibly I could manage to add absorption to the code but the problem is I'd need ~100,000 rays to image the whole gnomon and 30,000 even to check one digit at a time with rays in a 2D field of 60mm x 20mm spaced about 0.25mm apart.

The renderer/shader built into Onshape almost does what I need, it just doesn't cast light around objects and make shadows.  Is there any way to bend that to my needs?

Thanks

NeilCooke

For my script you need to draw a line that is the light direction and select the vertex at the end for the point light. I tried it on your model and it does seem to work. 

For your manual method, create a plane or mate connector at the end of each line, select it then press N for normal. 

NeilCooke

This is a bit rudimentary, but should do what you need:
https://cad.onshape.com/documents/72598ea70a78b9bf66126b3a

Gunter

Thanks, Neil, you're as responsive as ever.

Your feature doesn't work for me yet:  No matter what part of my gnomon I select, it complains that it "cannot determine rotation axis".  I'll have to analyze the code for why; maybe my structure is too complex.

Thinking about Onshape's built-in shader I came up with a partial solution of my own:  Instead of the "sun" casting a shadow from above, reverse the view and look into the pixel holes from below.  Depending on the viewing angle the "sun" should be visible through the active pixels.  With a black gnomon and a bright red "sky" wrapped around the cylindrical top of the gnomon I can indeed see which pixels are active at what view.  The solution is partial because I don't know how to define a viewing vector such as [0, sin(angle), cos(angle)].  I kludged up a fan of transparent flat sheets at angles between -45⁰ (10AM) and +45⁰ (4PM) in 5⁰ steps corresponding to the 20-minute resolution of the sundial.  Now I can count the sheet edges on both side of the centerline to roughly figure the angle.  But dragging the view with the mouse is awkward and I keep veering off the straight line which tilts the view on the wrong axes.

Is there a way to define the viewing vector?

Thanks

NeilCooke

For my script you need to draw a line that is the light direction and select the vertex at the end for the point light. I tried it on your model and it does seem to work. 

For your manual method, create a plane or mate connector at the end of each line, select it then press N for normal. 

Gunter

Awesome!

I didn't know that I had to have the light source on a line.  Thank you very much, also for the mate connector idea.

MBartlett21

@NeilCooke

Wouldn't you be able to use the opSplitBySelfShadow function and then offset the invisibleFaces that are returned?
https://cad.onshape.com/FsDoc/library.html#opSplitBySelfShadow-Context-Id-map

Gunter

I saw some suspicious differences in the results of the shadow feature script compared to looking into the pixels from below and made a test case with "secondary" surfaces not directly connected to the "object" face.  The results differ between applying the feature script before and after re-selecting the foot of the column as the object:

Edit (re-apply) shadow script after adding the extra shapes but without changing the object selection:

Re-apply the shadow script, selecting the column foot again:

Both shadows are wrong but in different ways.

It seems that the shadow script needs to somehow recurse to collect shapes/surfaces that are touching the original object shape.  I'll have a look but that may be beyond my feature script programming capabilities.

Gunter

OK, here is my favorite solution to my particular shadow casting problem; particular in that I need to check which pixels on my sundial gnomon light up, i.e. which paths through my object are clear when illuminated at a given angle.

I made a new empty assembly and inserted my gnomon,  I change the view to look at the bottom of the gnomon by clicking on the view cube so I know I'm exactly normal.    The active pixels will have a clear path through which I see the background.  Now I grab the mate connector that sits on the part's axis of rotation and drag to rotate it.  This opens a small dialog for the angle where I type in the exact angle I want.  And the dialog stays open so I can just keep typing in new numbers.

The response is instantaneous because the model itself is static, unlike when I rotate the part in a part studio.  There it's part of the whole model which gets re-evaluated with every change - much slower (several seconds) on my slow hardware.

sebastian_glanzner

@Gunter

Another solution would be the rendering software KeyShot Pro.

• Set the environment to "Sun and Sky"
• Chose a location, date and time
• Or set the Sun to a custom inclination
• Set the Lighting to "Product"

You can get a trial version of KeyShot Pro here:
https://www.keyshot.com/resources/downloads/

Here is a quick example how it would look like:

ethan_barbour

I was able to recreate @NeilCooke 's demonstration. But when I try it on my existing model, I get the message "No faces were selected for the extract surface operation.". Here is the model: https://cad.onshape.com/documents/a3888ef888ccf8a28b67c6f8/w/5416dfa1fbfc52c9ed6c9fc4/e/8b15ec5c03268f75a375858e?renderMode=0&uiState=624b4f4dbaf8243b56c33ec2

This is a house with the back porch, which has a post in the middle. The sun is facing the porch. I am trying to generate the shadow of this post. Any help would be appreciated. (BTW, when I recreated Neil's demonstration, it only worked if my light vector originated at the origin. I couldn't get it to work if I used any other point to make this vector. In my current model of the house, I am using the origin to make the light vector.)

S1mon

Since this thread was last active, there's also the addition of Render Studio (for Pro/Enterprise). Seems like it should be able to cast correct shadows, but I'm just getting started with it.

https://www.onshape.com/en/resource-center/videos/render-studio-photo-realistic-rendering-in-the-onshape-platform