How to build a holodeck, week 16 - Avatars

How does one represent themselves to the world? A tricky question, both physically and metaphorically. The apparel oft proclaims the man, according to the Bard. This week, I’ve started to explore Avatars.


Week 16 - skeleton tracking

Week 16 - networked skeletons

Avatars - where to begin?

“Avatar” is typically used to describe either a deity in manifest form, or a representation of somebody (or something, or some idea), often in a computer game. “Your” avatar can be your representation of “you”, as well as a channel for interactions both ways (from you to the world, from the world to you).

You can have no avatar at all (This is actually pretty uncommon, but it does work). You can have an avatar that’s visible to others only (typical in first person games) or one that’s visible to yourself as well (pretty necessary for third person games).

We’re all quite used to the idea of playing a “character” in a computer game, be that Mario or Lara Croft, and it’s no surprise that the representation of that character gives you lots of information about the environment in which the character participates, as well as the capabilities of the character themselves. When you play street fighter, you can identify your opponents capabilities just by looking at that character on the screen. If all the fighters had the same visual representation, you’d have a much harder time figuring out what moves or powers you were up against.

So it’s pretty clear that an avatar really matters, both to how you see yourself, and how others percieve you when they interact.

Representing an avatar in the holodeck

There’s a few key things I’d like to learn as I move towards holodeck version 1.0. Some of them are about self-identity, and a lot of that comes from the form and motion of your avatar in the world space. Some of them are about communication - just how much is communication improved when you have some form of realistic body to provide gestural queues? The last chunk of key information is the specifics of how to actually capture/create a realistic avatar with the time and budget constraints I’m under - this is another “How close can I get?” chunk of work.

Rigging and skinning

The typical way that games (and current social experiences such as AltSpaceVR) represent you is to have a rigged and skinned human (or humanoid) mesh. Here’s an example of how a mesh can be rigged (attached to a skeleton) and skinned (blend weights assigned) so that it can move and deform like a human.


Once you’ve got a mesh that’s rigged and skinned, you need to ensure you’ve got a nice quality textured mesh to go with the model. The texture can be scanned, or it can be created in a paint program.


Once you’ve got a skinned, textured mesh, you then need to make it move. There’s a variety of techniques here, including direct animation playback (moving the skeleton rig around to move the arms and legs) and Inverse Kinematics or IK, which lets a controller move an end node (i.e. the hand) and the IK solver works out where the rest of the body should be based on constraints (your arm can only twist this far, your bones are this long, so your back needs to bend like this to allow your hand to be there). The best games and movies will use combinations of both captured animation (motion capture), hand crafted animation, IK and other procedural tools to drive the model. My previous company had some fantastic tools like Morpheme which show how complex all of this can get.

Of course, a human isn’t the only way to represent an avatar - you can use robots, flames, or a floaty yellow ball - they all serve the same purpose, but they all have a different impact on how the player, and viewers, percieve your character.

Making a realistic human model is hard

Getting a good looking human model is hard, and the closer it comes to photo-realistic, the harder it becomes. Without getting stuck in conversations around the uncanny valley, I think we can probably agree that the characters in “The last of us” look pretty darned human, and the human-like characters in Altspace are not quite up to that level of fidelity.

The last of us:




and here’s a wonderful TLOU cosplay image by Jordan Farbridge.

TLOU cosplay

The Last Of Us is close to the pinnacle of quality when it comes to human models in games. There’s a few movies (such as Avatar, natch) that have really pushed the boundaries of what’s capable, but even now you can often tell straight away that the image is computer generated. The amount of effort (and budget) that goes into creating these characters is enormous. Constructing and rigging the models, applying textures, animating the model (and the face, and the mouth and eyes, and the hands) all take a big team of expert artists months or years.

There’s a great video here showing the development process of a single character, Senua, in the upcoming game Hellblade. You can see the amount of effort that’s gone into creating her, and the results are nothing short of astounding.

Doing this realtime with no budget

Here’s lil’ old me, trying to bring something to the party, and I’ve got a very constrained budget (both time and money) so I’d like to create human meshes and drive them with realistic animation, all in realtime. What’s the solution?

Well, this week I’ve totally skipped the “human mesh” part of the avatar story, and gone directly for a more abstract representation of a human. I’m using the Microsoft Kinect V2 sensor to track the position of a human in the holodeck space, and I’m then taking the joint positions and turning them into little particle generator points.

In the first video, I’m projecting the skeleton a few metres in front of myself in virtual space so that I can see myself moving around. This feels pretty darned cool in VR, and I’d love to try this out with someone else with the same setup (Kinect and Vive) - get in touch if you’d like to try it.

In the second video, I’m sending the skeleton node positions over the network, and reconstructing the fire avatar on the Tango (which can also move around the scene using Tango tracking).

I’m not (yet) using that skeleton data to drive a meshed avatar, but that’s the next obvious part of the puzzle. I also need to look at driving the resulting mesh using just IK and animations, instead of using the Kinect feed for two reasons. 1, most people don’t own a kinect - and 2, the results coming out of the Kinect are ropey as all hell.

Scanning tools and options

There’s a few apps and tools out there that use my current pool of RGB-D sensors (Tango and Kinect) to scan heads and bodies, but after trying out a selection of them (KinectFusion as an example) they’re all pretty ropey. I was hoping to use ReconstructMe but that doesn’t appear to support Kinect V2.

Some of the best consumer-level results I’ve seen are from the Structure sensor and the Itseez3D app, which can produce fantastic results for head and body scans. Here’s an example on Sketchfab from a few days ago by Roboindus:

RI011160605001 by roboindus on Sketchfab

The Tango, in theory, is capable of performing this kind of scanning, but in practice the quality and accuracy of the data produced mean the results are not anywhere near as good as the example above, and I’m not (yet!) intending to spend months or years creating tools to compete with Itseez - so it looks like I’ll be getting myself an iPad Air and a structure sensor in the near future to try and get some quality scans done.

Another option is the Intel Realsense developer kit, and as they are a lot cheaper I’ve got one on pre-order. Hopefully Itseez will support this hardware, if not I’ll be grabbing a structure sensor in the next month or two.

Turning a scanned mesh into a rigged mesh

I’m not an animator, so I need some simple tools to rig and skin the resulting mesh. Here’s an example showing Sketchfab’s Alban dancing, using a mesh created in Itseez and the Mixamo animation tools.

Gangnam Style by alban on Sketchfab

We’re still in the uncanny valley here (especially with the foot movements and some of the arm constraints) but these results are close to what I want to use, so I guess I’ll be going down that route in the near future.

Next week …

Next week I’ll probably look at getting the Kinect data to drive a Unity avatar, and get that synced over the network. Getting started on something along these lines.

Or, I might take one more punt at fixing up some of the known issues with my scanner, and get the skeleton tracking working in the Portals prototype.

Written on June 10, 2016