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How to make your own T-Rex?

3d artists Gael Kerchenbaum, Thomas Obrecht, Charles Chorein shared how they’ve created a 3d model of the dinosaur and helped it move in 3d. It’s not Jurassic Part yet, but it’s a start.

3d artists Gael Kerchenbaum, Thomas Obrecht, Charles Chorein shared how they’ve created a 3d model of the dinosaur and helped it move in 3d. It’s not Jurassic Part yet, but it’s a start.
A Walking T.Rex is a small project we set up together in order to create a tutorial for Gnomon Workshop. We were three artists involved on this short demo. The project lasted a bit more than a month; and finally we decided to release a short video breakdown.
Gael Kerchenbaum is a freelance character and creature artist who worked at MPC. Currently he is teaching 3D to student around French and Swiss schools. He talk about his process for creating the T.Rex.

I started to work on this model during a Workshop I gave in a school I go in on every month in Switzerland, the EPAC. At the beginning, I didn’t had any particular idea about this model apart from using it to teach Zbrush to my student. Then I was contacted by Charles Chorein, thanks to a former MPC colleague. Her name is Solene Chan-Lam, she is a wonderful texturing Artist! Charles, Thomas and I studied VFX in the same school, but we were on different promotions. We decided to team up together in order to take my demo model of the T.Rex to life.

When I’m doing model, I always love to start by an expressive concept sculpt. Doing model in bind pose is necessary for rigging, however I strongly believe that we cannot create model that share some emotion by not starting to put it at the beginning of the work. For this reason the model was a bit bended forward, it has its mouth with opened and the muscles were baked in as an écorché. I sent all the different WIPs to Charles and Thomas so we could always have a sight on the evolution of the model together.

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When the final model was approved, I putted it back into a bind pose in Zbrush by using the transpose tools. I refined the anatomy in order to get some clean joint position. Because Thomas needed to have the model to start on the rigging, I sent him a decimation that I used for retopology. This last step was pretty quickly; I only spent two days on retopology and one more on UVs. When already knew that we needed to make an asset for a VFX shot, so I decided to create 10 UDIMs. Those came really helpful when it came to get enough definition for creating scales.

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After the retopology, I projected back the details from my model in Zbrush and took the result into Mari. I started by painting the scales and all the skin displacement thanks to surface displacement textures. Regularly, I exported things out of Mari and Zbrush so Charles could have a look at the evolution of the model into his layout scene. The albedo maps was the hardest one to make. We needed to have something simple that works fine in the plate. However, at the beginning every time I tried to render the albedo in a look dev scene it looked faked. For this reason, I decided to over exaggerate the colors. I used the displacement as a channel mask to create ISO maps for the cavities, the scales, the scars… And then I used these ISO to paint on all the details on my color map.

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The spec and spec roughness was done pretty quickly. I only had to take my displacement channel, duplicated it and added some extra adjustment layers to have more control over every type of skin. Since we used the T.Rex from Jurassic Parc as a reference, when wanted to have some dry skin along with glossy scales.

Once I had everything ready in Maya, I exported all the maps and took them to Zbrush. I wanted to sculpt back some of the scale in order to give them more volume. The problem when using Surface Displacement photography for texturing is that you’ll end up having some small volumes even if you paint high volume scales; so you’ll probably have to sculpt them back in Zbrush. Because I had many UDIMs, I separated my model in many subtools. This allowed me to get a higher polycount for sculpting fine details.

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If you want to have a detail look at this workflow I encouraged you to have a look at Javier Blanco making of.

Thomas Obrecht is a senior animator. He works at Quantic Dream since a few years now. He explains his process for creating the rig and muscle system on the T.Rex.

I started to create a classical rig with all the basic controllers necessary for this type of creature. I made some IK / FK switches for the spine and the toes in order to have a smoother control when it came to animation. Gael delivered us 3 different LODs – same model with three different level of subdivisions. It was really helpful for me to have access to different polycount, this way I could reduce the latency when I had to animate the creature by using the low definition model.

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I made a second rig out of the first one. This one was dedicated to the high definition model in order to work with muscles and to get some extra details when the T.Rex started to move. The great point having two different setup that share the same skeleton was for me to avoid any performance issue when I had to animate.

I did the animation, then I isolated the moving skeleton in order to keep only the bones and exported it as a FBX file. Then I created a short batch script in order to attach the muscle rig on top of the exported FBX.

The hard time arrived when it came to paint the influence of muscles onto the high definition model. My framerate was too weak when I tried to use the Maya Paint Weight tool. So I decided to paint the weight of the muscle on the low definition model and transferred it onto the higher definition T.Rex by using maps. Afterward I added a second layer on top of my skinning in order to keep the primary skin. This allowed me to get some extra detail coming from the contraction of the muscles.

I also used the free version of the ngSkinTool. I recommend you to have a look at this plugin. It helped me to save hours of work thanks to its layers. I was also able to use it for map export.

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For the throat, I made some muscles with the Muscle Creator system. I then constrained the control of the muscles to the bones of the neck. I customized the way the constraints worked in order to avoid any weird squash effects. After I had setup my jiggle parameters, I created a noise expression on top of an independent controller to make the glottis shake when the T.Rex shout at the end of the shot.

Finally I exported the final mesh in alembic and gave it to Charles who took care of the render.

Thomas Obrecht, Senior Animator

Charles Chorein is CG Supervisor. He works at Double Negative in London and has a great experience in VFX. Charles was in charge of the supervision and look development on the project. He used the T.Rex to record a Look Development Tutorial in Maya for Gnomon Workshop.

Charles was the center point of the shot with the T.Rex . From the beginning of the project he helped us to keep a really clear sight over the creation process. After we decided to work as a team he set up all the working environment. Doing VFX is not only about being able to go and play with a software. It is also about being about to manage a team, to keep everyone in the same loop so we all know what is going on. We strongly believe that a good work always need to follow some good production steps. At the beginning we didn’t knew exactly how many days we would have to get this project done. So we decided to establish a one month project.

He started by establishing a place where we could all share our work together and keep a history of the advancement of the project. Slack, a chatting application that connected with Google drive, was used so could speak every day. The great advantage with Slack is that you can set multiple room if you need to work with many Artists. It also has a direct connection to Google Drive so you can easily share files together. All the links, the screenshots or the videos that we send for approvable are kept in the history of your slack’s channels.

Charles was in direct communication with Gnomon Workshop. On a regular basis Charles sent us some invitations on Google Calendar for organizing some Skype review sessions. We shared our screen so we could get approval for our work, and it was sent directly to Gnomon.

At the beginning of the project we found a picture that was useable for commercial purpose without any restriction. It is always hard to find that kind of content, I recommend you to have a look at content under Creative Common Zero if you need some. Once we found a plate, Charles made us a layout scene so Thomas could start to animate in it. He also set up all the lighting and HDRi so I could bring my model and texture into the scene and have a quick sight if things work.

When the model was done, it was rendered in Maya with Arnold. This part was tricky because we had to deal with an animated model that walked through 320 frames. Because we had to render everything from different places, we had to find a way to share our files on the same place. Never under estimate the amount of space that you’ll need when working on animation, even for a small project like the one that we did. We also had to take into consideration that the deadline was short, and uploading files is always dependent of the internet connection of each members of the group.

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Finally, Charles recorder his Look Development tutorial for Gnomon. This one has been released this week and can be accessible on the follow link.


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Charles Chorein, CG Supervisor

We hope you enjoyed following our creation process. This was an amazing project to be part of.

Interview conducted by Kirill Tokarev

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