V-Ray’s Dirt map enables you to quickly add detail and depth without generating large bitmap textures. Have a look at the documentation for examples of what each property does. For this tutorials I’ll be using a simple road section as example model to demonstrate how to set up and control the Dirt map.
Download sample SketchUp Model (SketchUp 8, V-Ray for SketchUp 1.49.01)
The starting point is this very simple scene. At first we will look at just the road material and use use plain colours in order to see the effects of the Dirt map.
Starting Point
The concept is simple, use a Dirt map in the transparency slot so a second underlying diffuse layer will bleed through.
Road Material
In order to control the effect just for the road surface it has been grouped and the Dirt map is set to “Ignore other objects”.
The other key property here is “Invert Normal”. When you inspect the SketchUp model you will see that some of the edges of the road geometry is extruded downwards a little bit. This is done in order for the Dirt map to generate the dirt where you want it.
Road Geometry
To clearly illustrate how the dirt effect looks I made the underlying diffuse layer red.
Dirt map as transparency
Observe how the Dirt map in the transparency map let the underlying red diffuse show through around the areas where I had extruded the edges. When we use a dark grey colour for the second diffuse it appear like this:
Dirt mapped road
If you wonder why I didn’t just use the Dirt map in the main diffuse layer it is because I want to have the opportunity to use the Dirt map with textures which I can scale and position within SketchUp. Lets expand the example by adding grass to the model.
Dirt map with textures starting point
Using the same setup as with the road material we create a second diffuse layer with a Dirt map in the transparency of the top diffuse layer. When creating these setups I usually use a bright colour such a red to visually ensure I’ve set them up right.
Adding dirt to the grass
Again I grouped the grass by itself and extruded the edges where I wanted to see the Dirt effect. The result is a scene with more subtle details that enhance the bordering edge between materials and objects. The diffuse underneath was a dark green colour. I could also have used a texture for the second diffuse in order to create even more variation.
Road and grass dirt mapped
In the final scene I added some extruded edges along the length of the roads to break up the flat surface even further.
Wireframe
Note that at the T intersection the centre lines does not meet – I added a slight gap in order for the dirt mapping to look softer.
Final Result
This simple method let you quickly flat boring surfaces with subtle shading without creating huge texture maps specificity for that geometry. You can easily reuse the V-Ray materials as long as you create and organize the geometry in similar fashion.
Observe how the quality of the subdivisions affect the appearance of the dirt. Some times I prefer to use less subdivs because the noise fits well.
Subdivs Examples
Sweet! Many thanks.
this is really cool thanks!
I would like to use this to create a rough edge like grass growing over a rocky path is there a way to sort of randomise the falloff? its hard to explain. in my model the the fade between textures looks too perfect along straight edges is there a way to make a smoother fall off and then jitter randomly. Im new to texblend and cant seem to get this to work inside.
Im also wondering if there is a way to add a multiplier to the dirt transparency map. I can adjust the radius fine but i can’t seem to make it full or 100% transparent on the edge. the second material always shows though this is not ideal if i’m joining my soft or faded material to the same but solid colour with no dirt map.
Using this for roads is amazing! I have always wondered if it was going to be possible to create a texture along the length of a road on a curved surface. and saves me darting in and out of photoshop, I can’t thank you enough.
heres a link to my first road.
http://i.imgur.com/7kn0M2V.jpg
this is sort of what i’m going for. but just around the boundaries.
http://3ds-sketchup.blogspot.com.au/2011/08/tutorial-grass-and-gravel-displacement.html
I haven’t tried this, but perhaps you can add a noise map to the dirt map? Instead of the TexAColor maps.
Hey, that roads looks nice!
As for the multiplier, you can adjust the intensity of the dirt mapping by tweaking the Black and White color channels of the Dirt map. Remember that it acts as a transparency map in this case – use any values between black and white to get more fine tuned results.
Just thought I would update another use for this method.
http://imgur.com/SDz6V6u
A quick way to make a rusted roof around the edge of sheets.
I unchecked the ignore other objects box in the texdirt settings and used a bunch of clear boxes as the intersections. The rust material is above the reflection layer so it stops the refection coming off the roof where it is rusted.
Hope this helps someone!
Monkers.
Me again, just thought I would post more of my findings for anyone following this post.
http://i.imgur.com/JYgsZ7j.jpg
my understanding was that the ‘dirt’ was calculated based on the angle of the intersecting face, or at least part of the calculation is from this. However if you look in the image I posted above it seems to be effected buy the thickness of the volume.
I tent to model in solid volumes which makes this a bit of a pain when when I have to go through and remove faces like in the image below. the bottom face is removed. which is a pain because that was serving as my eaves and ceiling.
http://i.imgur.com/mBP9LIv.jpg
Cool! Thanks for sharing!