Render leaves trails of blue dots

My render (on mid-2011 MacBook Air) leaves many trails of blue dots on an otherwise very acceptable render. Sort of in a grid pattern with several lines of densely spaced blue dots parallel to the 3 axes. Very annoying. I have tried all the anti-aliasing settings. I have tried different backgrounds. Not sure where to look next.

After looking at this some more, the blue dots seem to be lining up along the texture tiling boundaries. Must be some holes in the texture! :wink:

See attached image…

Hi Matt - I believe this is a consequence of how the mapping is applied - I think it’s fixable - @BrianJ, didn’t you track this down recently?


I think this issue is the same as

Make sure the mapping widget isn’t smaller than the object in the meantime.

Any luck?

OK. Something to look into. What exactly is the “mapping widget?” Is that the actual .png texture file?

I created the problem-causing .png textures from snippets of photos. They are very much smaller than the object. I’ll have to think through how to make them bigger than the object. That seems like an unfortunate constraint.

The MappingWidget command will display the mapping widget on the screen for the selected object, MappingWidgetOff will hide it. A mapping widget is the graphic interface of the texture mapping method chosen for the object in the Properties panel>Texture mapping section. For instance, a planar versus cylindrical projection of any image textures in materials that are applied.

You can increase the tile amount of the image texture within the material after making sure the mapping widget is larger than the object to work around this issue… if it is what I think it is.

If you can upload a portion of the model as well as the texture used in the applied material, I can tell for sure.

That seems to do it, but still trying it out. So, I can just stretch the mapping widget with the Gumball to be larger than the object with the texture?

Yes, or use a bounding box option for a given mapping method to make the widget the smallest boundary. For instance when you click Custom>Projection: Planar for the mapping in Properties and then select the option in the command prompt to size by bounding box. You may still need to adjust with the Gumball depending on if the texture is stretched still after adjusting the texture’s tiling in the material.

I spoke too soon, still getting blue dots (pixelated noise). I am confused on how this thing works. Whenever I fix one surface, the previously fixed surfaces and mapping widget get messed up. Maybe I need to make a unique material for each surface.

Can you provide the 3dm file or a portion of it that shows the issue as well as the image texture used in the material?

Hi Brian,

Attached is the whole model (sorry). Hopefully the layer names describe what is there, but ask a question if you are looking for something.

I would love to see a flow chart or block diagram of how all these various objects (geometry, material, texture, mapping widget, etc…) interact to make the display, as well as how the various settings control the objects.

Pixelation is on the various roofs (roof shingles) and main house siding (siding shingles). I have been working mostly on the shingled side of the house that extends from the blue front door entry area, back past the sliding glass door, and then alongside the attached barn (i.e., the left side of the main house). I had also been working on the roof of the green woodshed. I get the shingles on the left side of the house looking correct and the mapping widget set to the size of that surface, then i move around to the other (right) side of the house and work on that side. Then I come back to the left side again and the mapping widget on the left side is completely different (smaller, in a different plane). So I am at a point where I would like to read some detailed instructions that describe what each option (in the material setting, texturing, rendering processes) controls. Is there such a resource somewhere? I have not stumbled on it and there are too many options to continue with the trial and error approach.

Model (zipped):

Siding Shingles:

roof shingles:

clapboard siding:

asphalt road surface:

The other textures used are from within Rhino.

7 Pitt St Rev (4.43 MB)

Hi Matt,

Yes, this is the same bug due to the size of the mapping widget. I made a video for you to explain the work around…

Thanks Brian. Good stuff. Try then going to the next (front or right) surfaces.


The DIR command. I have been wondering how to swap U and V. I’m sure I saw it in a video somewhere at sometime, it has just been forgotten.

And I see how the texture scaling/rotating I thought I needed to do during the texture setup likely changed the mapping widget size and orientation.

It is interesting that in your video the surface picked up the wrong texture (clapboards rather than shingles). I just experienced that problem, as well, for the first time. Not knowing how to get back to shingles, and after trying unsuccessfully to reapply the right material, I finally just deleted the mapping widgets until No Selection seen under the MappingWidget command. That seems to have solved all the problems (so far)! Who needs mapping widgets? But, how can that be? Is it possible to accidentally generate extra mapping widgets?

Back to your video, what happens when you go and texture the adjacent (front) wall? You will need to enter a different tiling parameter in the material settings (at least that is my experience, maybe because the surface is a different size and aspect ratio?), which will mess up the first wall, won’t it, since this is in the material section, which is common to all objects using the material.

Pandora’s box.


Click Swap UV in the command options to the left when running the command.

I had to reassign that texture so it wasn’t that it was wrong when I opened the file just that it was missing.

Mapping widgets are an important part of making sure textures in materials look the way you want. You can have more than one channel for an objects texture mapping properties but I suggest just using channel 1 when asked during the set up. This is the default and any new mapping set will replace the existing channel 1 assignment.

If you Join the wall surfaces together and use a Box mapping method also set to bounding box, you can have one material for both.

Thanks for all your help Brian. I did eliminate all the blue dot pixelated noise from the rendering. I stumbled upon a slightly different process than we discussed that I think works really well:
Set the U and V tiling parameters in the Textures part of the Material>Edit menu at 1.0 (or whatever values you want for the baseline material),
These values stays constant; there is no need to adjust this value,
In the Texture Mapping menu hit the “Size to Object” button to size the mapping widget to the full size of the object being textured,
Enter suitable values in the UVWRepeat entries (all the way at the bottom of the Texture Mapping section),
Here, larger values entered make the texture features smaller,
Also, adjust the UVWOffset and UVWRotation values as necessary to align the texture features.

This process enables control of the texture on each surface individually without having to join them and without affecting the previous texture mappings which happens if you change the U-V tiling parameter in the material menu. Therefore, the same material can be used on multiple surfaces, each with different texture feature sizes and orientations.

Again, thanks for your help.

I do have another question on remapping U-V. Say I have a right-triangle planar surface with U along one of the two shorter legs and V along the hypotenuse, can I easily change V to be along the other leg of the triangle, without redrawing the surface?


Yes, that’s a good use of the object property of texture mapping versus having multiple materials for different tiling amounts. Nice job.

If I understand your question correctly, the original surface was made with a Sweep2 resulting in a zero length edge at one point of the triangle. This will make U or V follow the diagonal edge and swapping them with Dir won’t change this. On the other hand, if you use the border of the triangle (DupBorder) and make a new PlanarSrf with it, your U and V will be aligned with the right angle.