Procedural Locomotive

For this project I wanted to simulate the movement of a Walschaerts valve gear in Houdini. I knew, before I started, that it was going to involve a good amount of sine and cosine expressions considering the repetitive movement.

Reference Material

Breakdown

Each part of the system is connected procedurally, not physically. Since they are all moving in unison, it just looks like they are connected. Each part is also based on the same global variable, $FREQ, which represents the frequency of movement.

The wheels are simply rotating on the Z axis based on the frame number, $F, and $FREQ. As for the bar connecting the wheels, since it has no axis, and does not rotate, it must be translated in the X and Y axes. To acheive this we need to use a Cosine and Sine function on the X and Y transformations respectively:

tx = $AMP * cos($F*$FREQ+$p)
ty = $AMP * sin($F*$FREQ+$p)

$AMP controls the maximum and minimim distance the Sine curve can reach from zero, the amplitude. So in this case the radius of the circle the object forms when moving. $p is the period of the Sine curve, a shift of where in time the Sine curve is currently read.

The bar in the left movie has Sine curves applied to both the translation and rotation. It is being translated in the X axis back and forth with a simple Sine curve and also rotated in the Z axis with another Sine curve. The pivot point is on the right end of the bar. This simultaneous movement gives the illusion of it rotating with the wheels while driving the crosshead arm shown in the last movie.


+ Links
Walschaerts Valve Gear - Wikipedia

Kitchen at Night

For this project I wanted to simulate light fog coming through window blinds. As the camera moves I wanted to see changes to the light moving through the fog.

Background with no Light Fog, Depth of Field, or Occlusion.

Adding Depth of Field.

To add depth of field, I needed to render out a Z-depth channel. After that, in Shake, I blurred the image based on the Z-depth information.
Adding Light Fog.

To get the light fog pass, I applied a black surface shader to all the objects in the scene. Then I emitted a white light fog from the light beind the window. This created a mask I could use in compositing.

Adding Occlusion.

The occlusion is then added to get the contact shadows.


+ Links

3DRender.com: Lighting Challenges

Flying Cards

This is a Houdini particle simulation. Models of cards are instanced on a particle system. A curve was drawn in the outline of the human figure and moved out in the distance in front. Then one particle is emitted per point in the curve. The particles are then grouped randomly into 5-6 groups. Then the particles in each group are given a random velocity and the groups begin to move at different increments in time. This ensures that the cards will not form the shape of the human in the air before they hit the wall.

Breakdown
There is a random rotation applied to each of the particles as they move. Once they hit the wall, they stop rotating.

Here is a previous clip I created to test things like textures, particle behavior, and motion blur.

A random collision result using Switch SOP.

The card models are given a random texture from these playing card texture files.

Candle Match

For this project I chose to take a photograph of a small candle outside and create a 3D model of it and match it to my photograph.

Analyzing the Reference

Comparison of light and dark environments

When in a brighter area, more detail of the texture can be seen such as the small splotches of blue and the subtle scratches on the surface. Also, the candle appears to be slightly reflective and has high specular highlights along the rim and the sides. Most of these details are less apparent in darker areas. This texutre also has a fairly high diffusion as seen in a photo below.

Slightly bluish and transparent shadow

Because of the direct sunlight, the shadow is fairly linear and does not widen out as if it were being lit by a spotlight. The is also fairly sharp around the edges, a little transparent, and has a blue hue to it. This blue hue is most present on a bright colored floor.

Examples of reflections

Since the candle is slightly reflective, the reflections will change based on its surroundings. The color of the specular streaks on the side will be a color similar to what it is standing on.

Re-creating the Candle

In recreating the material for the candle I first noticed that its rim was a darker, solid blue. So I chose a ramp for the color node which is just a solid light blue to a darker blue, then back to light. The spotted texture was created by connecting noise to the ambient color. Next I added a subtle bump map to imitate the small scratches. Next I adjusted the eccentricity and specularity to match the photograph.

Diffuse, Specular, and Occlusion Layers

The Maya scene consists of three directional lights. One is the main light that emulates the Sun and is the only one that casts shadows. The other two are on the opposite side of the candle and only emit specular to the candle and only exist in the specular layer. This made it easier to control the highlights and imitate the reflection on that side by adjusting the color and intensity of the light. The lights are not pure white; they have a slightly yellow hue.

The occlusion layer is very subtle because if the direct sunlight. I adjusted the behavior of this layer by lowering the 'spread' attribute in the 'mib_amb_occlusion' node in the surface shader.

Compositing
A good majority of the project was done in Shake. Since I rendered in layers it was much easier to adjust parts of the image individually. The main parts that were adjusted were the blur and color of the shadow and the brightness and contrast of the diffuse layer.