Learning Houdini Journal 17: Bus Front Details

Mar 09, 2016 at 10:14 pm by -gToon

This is the seventeenth entry of what will be a year-long journal on learning the 3D application, Houdini, created by Side Effects Software. Houdini is a sophisticated application that is widely used in the production of visual effects for Hollywood films such as Big Hero 6, Mad Max: Fury Road and many others.

In my previous Learning Houdini Journal 16, I started a new series of tutorials created by a favorite Houdini instructor: Rohan Dalvi. The course is called "Procedural Vehicle Modeling". I completed the first chapter which entailed modeling the front part of the bus. Now, I'll start working on the window, the door, the grill and the tire cut....god willing.

Chapter Two - Bus Front Details

Another frustrating lesson due to the degree of difficulty and my lack of understanding. I thought I had made good progress in Houdini with the Intro course I finished last month, but this series of tutorials are a bear for me. Rohan Dalvi, the instructor, does a good job in his presentation, it's me.

Firstly, I discovered I had angled in the wrong side of the bus front. Thinking that this was exactly what procedural modeling is designed for, I went back to the node that came just before I moved the edge of the box. But, alas, I couldn't figure out how to get it fixed. After banging my head for an hour, I simply erased the nodes and started over. Tedious, but helpful in that repetition cements the process in your memory. I am committed to learning Houdini and will start over as many times as I have to to get the lesson right.

End chapter 1 -end chapter one model (front of bus)

Mr. Dalvi Decides to do a Boolean

Mr. Dalvi explains why he chose to use boolean operators for the bus front details rather than the traditional polygonal modeling:

"The initial idea was to go the normal polygonal modeling route [for bus front details]. Two issues with that: One, polygonal modeling will require us to increase the number of segments quite a bit and the modeling starts to get really complex, two, how do you control the door/windows parametrically if you've just done a polygonal inset, etc? Since the structure of a bus is primarily straight lines, I decided to do a boolean"

If you are unaware of what boolean operators are in constructive solid geometry modeling, check the wikipedia entry here.

The Boolean Door

Basically, Mr. Dalvi uses a bounding box + boolean operators to create the four elements for the bus front details. Again, I found the idea clear, but the process difficult. I had to stop and start over several times and am still trying to work out the Houdini expression bbox (bounding box). I can get the expression correctly written, but somehow it never seems to put the bounding box in the correct place. In the picture below, you can see that the bounding box (red) is attached to the rear of the model whereas it should be attached to the front of the model where the door should be.

bbox mistake

bbox("../size", D_XMAX) is the expression. I place it in the X axis of the center, but it just doesn't work. I'm not sure what I'm doing wrong, but I'll have to start over and go through the process step-by-step to find out where I'm making a mistake.

I have a feeling that once I get past these initial chapters and get familiar with Mr. Dalvi's workflow, I'll move much faster. For now, it's shake my head and pull my hair time. :

Next: Starting Over on Bus Front Details