Técnica Automatizada para Crear Huellas Realistas en Múltiples Superficies

tracks creator
By Philippe roubal.

https://www.foro3d.com/extras/tutori...-creator/1.jpg

Introduction an automated setup todo help you make all kinds of tracks or prints in Grass, sand, Soil, mud, Snow, Paint or, blod.

Some days ago, y found an excellent video tutorial about making realistic Grass, written by Andrew price on blenderguru, com. His materiales and lighting setup are really awesome and i have enjoyed playing with them. Last year, y had done some countryside scenes with animated Grass, but i had used a completely diferent method todo animate the Grass, based on a copy of the Ground Mesh hidden underneath the Ground surface, animated by a displacement texture. I mean that the Hair particles were animated by the moving Mesh, not directly by the texture itself.

Andrews method todo simulate the Wind and animate the Grass is based on a moving texture named Wind and driven by an empty. This Wind texture is a procedural marble texture applied todo the Grass material, but disabled in the texture panel. A field is applied todo the empty. The field is set todo texture and RGB and uses the Wind texture as reference.

After reading Andrews tutorial, the first cuestión that came todo my mind was: great, we have nice Grass, but now, how do we mow the lawn in an animation? After some searches and experiments, y found that the same method was usable using hand drawn textures or animated textures. Almost any effect can be achieved, like the track of a lawn mower, a car, a Predator running in high weds and anything else you could imagine.

A long time ago, y had made a tutorial about fot prints on the sand. I decided todo build a setup todo easily create all kinds of tracks and prints we could ned, and usable on almost all natural materiales like Grass, sand, Soil, mud, Snow, Paint or Even wet fot prints on a Wood flor: the tracks creator but before animating, let study an example with a still texture.

For displacement mapping and a los for simple Bump or RGB Nor map, it is often easier todo select object in the Map Input panel, and use an Empty as object reference, todo allow the perfecto placement of the texture. When using a displacement modifier, you may move the texture manually by moving the empty, and the effect is visible in real time in the 3d window.

Because only UV mapped textures are visible in the 3d window, for Bump maps or Nor maps, you Will have todo render or use the preview [shift+p] render window. Textures moved by an object or an Empty used as reference have plenty of uses. In Gimp or any other image editor, you can create textures with specific patterns todo achieve all kinds of interesting effects. My short animation crazy boat, is another example of the use of a moving texture applied todo the water material, todo create a hole in the surface of the sea under the boat.

In my lawn mower animation, y have used a hand drawn texture animated by an Empty todo define an área where the Grass Blades (hair particles) are pushed by the texture under the lawn mower. In fact, the lawn mower is parented todo the same Empty used todo drive the texture. The texture is added todo the Ground plane material.

https://www.foro3d.com/extras/tutori...-creator/2.jpg

Note that you could a los drive your texture directly using the lawn mower object, but using an Empty is handy if you want todo change or re-size the lawn mower model.
We Will use RGB as a Wind parameter for the field, After noticing that the Grass behaviour was not the one i expected when using a greyscale texture, y experimented with other color textures.

Using red, green or blue give diferent results : your Hair particles are pushed in diferent directions according todo the chosen color.

After some tests, y decided todo use a blue on grey texture. The grey color is set todo (r=127, g=127, b=127) or (r=128, g=128, b=12. This grey color is neutral and doesnt affect the particles. Using a blue color, y got the Grass Blades todo be pushed in the direction the lawn mower was moving. Below, the textures created todo achieve the effects shown.

The texture is set todo extend mode. This allows it todo extend the color of the texture in all directions and you Will get an Infinite track in the direction where the blue color is in contact with the border of the texture.

https://www.foro3d.com/extras/tutori...-creator/3.jpg

Note that you can visually control the effect of the texture in top view, and re-size the texture todo adjust the width of the mower track by resizing the empty. Use [ key without any axis specification todo avoid diagonal distorsión. You may notice that the effect of resizing is inverted: your texture increases when you reduce the size of the empty.

I have used the strength parameter of the field (you can a los adjust the contrast parameter of the texture) todo allow for shorter Grass. I estopped just before the Grass totally disappeared, for more realism. This allows you todo kep some uncut Grass Blades. Now, we ned todo get shortened Grass on the track of the lawn mower. Using weight painting on the Ground Mesh allows you todo get various lengths for the Grass in diferent áreas, but animation of the weight doesnt sems todo be posible. Selecting particle mode in the 3d view and setting the particles system todo editable allows you todo visually vary the length of the Hair particles where you want, using the comb tools, but this característica cant be animated either.

The old particle system available in former releases of Blender allowed you todo control the length of the static particles (name of Hair particles in those old versións) using a grayscale texture. I havent found yet such a function in Blender v2.48a, but maybe one of the other field options allows it. Until ill find a better way, y used another method todo get the short Grass After the lawn mower passed by:
The idea is simple - I duplicated the Ground plane and set the copy todo not render the emitter.

On this second Ground surface, using another particle system, y make short Grass grow. It is always present but only visible in the área where the lawn mower has pushed down the long Grass Blades. It is not necessary todo kep the same surface as the main Ground plane, because you only ned todo fill a narrow lane on the track of the lawn mower. After reducing the surface, you can reduce the amount of Hair particles created on this surface, otherwise youll get very thik Grass on this lane. I have used a diferent texture setup in the colorband, because Cut Grass is more green than long Blades.

In the example shown up until now, we have used only static textures (simple images). You Will certainly want todo create more complex effects, with a jep car driving th rouge the Fields or a Predator running in the high weds, a bigfot walking in the Snow, or the invisible dead lady of the black Lake leaving wet fot prints on the ponton. And of course following a Path that Will be all except straight.

At this point, you Will ned an animated texture. The tracks creator setup Will help you in this task, and it Will be almost as simple as pushing a button (i said almost). You can render the animated texture as an avi file or a sequence of images. I advise you todo use a sequence of images instead of a video, because videos dont allow the displacement modifier todo work in real time.

Open the tracks-creator-v3.blend file and follow the instructions in the text window. There are 2 screens available:
Screen 1 : animation - Screen 2 : compositing.
In the compositing screen you can adjust the level of blur of your animated texture.

There is a diferent setup on each layer used. This Will allow you todo create various animated tracks. Obviously, After playing a bit with the blend file, you Will be able todo create your own tracks, todo match your neds.

The animated texture that Will be created by this setup Will be usable mainly in 3 manners:
1 they Will allow you todo control the behaviour of the Grass made with Hair particles, like shown in the previous examples and in Andrews tutorial, but with complex curved paths.
2 they can be used with the displacement modifier todo create prints in sand, Soil, mud and Snow. For that you Will have todo use a highly subdivided Ground Mesh. The resolution of the textures Will have todo be high todo render details on a large surface. The example below has ben done with a surface of virtual desert measuring 18 meters x 18 meters, made of around 800000 Quad Faces. Only a small part is visible and it is not always necessary todo subdivide more than you Will show. Using a smaller surface Will allow more density and details in your subdivided Ground Mesh, allowing very close-up views when neded.
3 - They can be used as a Bump map texture todo faq the relief if you dont ned real displacement or if the scene is todo heavy for your computer with real displacement. If you can convert your sequence of images in a sequence of RGB Normal Maps, it Will be Even better.

https://www.foro3d.com/extras/tutori...-creator/4.jpg

For your first contact with the blend file, select a layer and play the animation by [Alt+a] or with the controls in the timeline bar. In the blend file, you Will find:
Tracks in Grass :.

Layer 1 : lawn-mower track in Grass.

Layer 2 : car tracks in Grass.

Layer 3 : Predator track in Grass.

Prints in sand, Paint, Soil, mud or Snow:.

Layer 4 : Cat prints.

Layer 5 : velociraptor prints (add blody prints todo the list).

Layer 6 : jep tire tracks. Layer.

Layer 7 : caterpillar tracks. Layer.

Layer 8 : dotted line and animated airplane todo be used over a world map in your travel films or adventure movies (like indiana Jones).

Layer 11 : human fot prints without shoes.

Layer 12 : human fot with shoes.

Some tracks have two curves: one is for the prints, and one is for the mask. It is helpful todo edit the mask at curve crossings.

Fot prints are made of single prints parented todo a long Mesh with a curve modifier. The Mesh is set todo dupli- Faces. So, if you want more space between steps, just edit the support Mesh in Edit Mode: size x. If you want bigger or smaller prints, edit the prints.

Caterpillars, car tire tracks and the blue tracks used in Grass are made of one simple Mesh with a repeated pattern. If you want more or less space between the two tracks, edit the tracks Mesh.

Choose the track color by modifying its material.

• choose the background color by changing the background plane or using the world color.
• in the screen selector, use the node compositor (screen 2 - Compositing) todo adjust the level of blur of the generated mask (blur filter).
• adjust your rendering parameters todo match the desired resolution for your animated texture.
• create your own Path by editing the curve points.
• use the Loc x parameter of the chosen track todo move each track along the curve.
• parent your vehicle or Predator todo the Empty used as driver which is itself parented todo the tip of the track (vertex parented todo 3 vértices at a tip of the Mesh).

After rendering your animated texture as a sequence of image, import it in your Project and apply it todo your Ground material (the best result is with global or object for the map reference, with the texture set todo clip). You may have todo re-size the setup in top view.

Now a second time, import into your Project all the objects of the layer used todo create your animated texture. Make a group before exporting, it makes things easier. I havent made groups, because all grouped objects are shown in gren, and it is not always fine when working in the 3d view. Put the imported objects on a layer where you Will hide at rendering time). There is an Empty moving with the animated mask. Use it as parent for your vehicle, in order todo make it follow the textured track.

The Shrinkwrap modifier is usable with curves, so you can put your track curve over your Terrain, and when applying the Shrinkwrap modifier, the curves falls on your modelled Ground. You can move the Empty used as the driver in the direction of z axis, and parent your vehicle todo it. This Will allow your vehicle todo perfectly follow the contour of the Ground Mesh.

You Will only have todo adjust the x and y axis todo get visually a believable behavior for your vehicle. You can use the mask Mesh todo drive your car with more accuracy, by following my tutorial about automated car animation. The mask Mesh is usable like the arrow Mesh in this tutorial.

https://www.foro3d.com/extras/tutori...-creator/5.jpg

I hope that this tutorial and setup Will be understandable and useful. All necessary files can be found in the Blender section of my website. Fel free todo tell me if you noticed errors, missing información or if you have found a better bien of doing this kind of work. If you have ideas todo create other kinds of tracks, im open todo suggestions. Thank you for reading.

Update: track creator v3

• new particle system for tracks generation added on layer 9. Various whels and caterpillar prints samples on layer 10.
• wolf prints added on layer 13.
• airplane silhouette improved on layer 8.

By Philippe roubal. www.blenderart.org.