Motion capture LAB documentation:
Project: Calibration and Rigid body Lab
Date: 2019.09.07 4 p.m.
Location: NYU Black Box Theatre
Participant: Yundi Jude Zhu, Qiushi Lin, Ryan Grippi
Goals:
Calibrate the room and create rigid bodies with unique names.
Things to try out:
What kind of objects track well?
What different scenarios cause occlusion?
Make a new rigid body with a prop in the room!
Can you make a person out of rigid bodies?
Can you act out a scene with only objects?
Steps:
Use Motive to collect live motion capture data
Use wand to calibrate the space
Set the ground
Create rigid bodies
Record body movement and collect data
Live data output to Unreal
Calibration
Key notes:
OK, this is a wrong demonstration of wanding. The movement should be slow and try to cover as much area as possible.
Use the Motive to capture live data. Motive is very straightforward and user friendly. Just complete the upper right four icons to finish the process.
Mask out all the lights: basically just to make a mask like in Photoshop. Make mask visible to automatically ignore some irrelevant shiny dots. So that the canvas is neat and tidy, and only the markers are being captured.
When wanding the space, try to cover all the latitude and longitude of the space to make sure at list 10,000 samples are captured from each Camera. The more samples the better result. If a camera is not capturing enough samples, hit the frame of the camera will highlight the actual camera (yellow lights), and the wander can walk to that camera and do more wanding movement. The movement should be like slowly brushing the walls, or wiping cream on a cake. Be careful the T-Wand is super expensive and should be only held either in our hands or on the hook.
Calculation: When all the cameras have collect more than 10,000 samples, hit the “calculation” button to calculate the space. Wait for about a minute or two and if it shows “exceptional” then we are done!
Set the ground: After the calculation, the software will generate a virtual space without a sense of plane. So we need to use the L-shape calibration tool to set up the plane. Make sure the “z” is pointing to the director/performer/audience. It should be facing the center of the stage. After that, all the 16 cameras will know where the ground is. Make sure the L-shape calibration tool is safe and back in closet.
To save the ground means to create a project. Save it properly on D Drive (not c drive) with a legit name.
Calibrating the space
Rigid Body
Key notes:
A rigid body consists of at least three markers. Four is the best. Because sometimes one of the markers may be covered during movement. If the marker is less than three, the rigid body will collapse and lose signal.
The Black Box theatre can contain about 25 rigid bodies at the same time.
After setting up the assets with at least three markers, use the mouse to select all the markers and right click to create a rigid body from selected markers. On the right panel, we can name the rigid body and change their features.
The middle yellow dot is called centroid. It’s the core of the rigid body.
This is the very first magical moment in Motion Capture when select all the cameras eye on the selected markers. Screenshot courtesy of OptiTrack
Rigid body number 1!
Recording movement
Key notes:
When the rigid bodies are all set, hit the record button to record the movement. Motive is very straightforward like any video recording and editing software. Ready, Action, Cut.
Always have two takes in hand. One is the best performance. One is the best data. It’s all about data eventually. We need to make sure the data is easy to read and shows clearly what the movement it. Make sure all the markers are fixed and steady.
Data streaming
Key notes:
Unreal uses the same IP address with Motive, so that we can see live data output being transfered into 3D models.
In Motive, click on the rigid body to see “Streaming ID”; in Unreal, type in the streaming ID to live transfer datas into 3D models.
Always make sure that the markers are visible and never moved.
My experience
In this lab session, I created four rigid bodies with: stick, chair, tennis ball, and a plate.
I make a lot of videos for my full-time job. So the first idea came to my mind is to make a rigid body that can become a handy video camera in the virtual space. Firstly, I tried out the stick. It’s light and very straight. I put three markers on the top, the middle and the end. Each marker is on different side of the stick, so that I can also get the diameter of the stick. When output the data to Unreal, the stick rigid body makes a very handy video camera that I can hold on each side with two hands and do steady horizontal movement, up and down, and slider movement. When pushing up the stick, I found the hidden upper floor with all the golden gems that has gravity!
Later on, our team thought the chair with wheels will make a much more steady video camera that can do all the follow up shots. In the beginning, we put three markers on the chair, but one of the markers keeps falling to the ground and we lost track of the rigid body. That’s how I learned four is a better number. When data streaming with Unreal, one of team member was sitting on the chair and his body covered a marker, which also destroyed the rigid body. Thanks to the chair, I learned a lot about rigid body and streaming ID.
After this, we tried to make a first person shooting game with three rigid bodies. We put three markers on a tennis ball, which is also very easy to lose track because holding the ball with hand will accidentally cover one of the markers. We tried to use the chair as the camera, and make the stick and ball into 3D balls. Later, we changed the tennis ball into a box cover. The plate-shaped cover is flat and became a much steady rigid body to handle.
I created my first rigid body with three markers on a stick.
Super handy and steady video camera from the stick rigid body
The stick camera can also make super cool camera rotation and transitions for cinematography and video editing.
Of course the stick rigid body can also become a fancy weapon.
Fancy weapon!
The rigid body chair. In a test run, we accidentally sit on one of the markers and the chair was lost track…
We also tried to combine two rigid bodies together. If we use the chair as the camera and the stick as an object. Then we will get a steady shot of first person perspective. Super cool!!!!
We changed the tennis ball into a plate, which is a much more steady rigid body!
Summary
I had a lot of fun in the Black Box. When creating the rigid body, it’s important to think the final shape and movement of the virtual object. Sometimes it’s unnecessary to make a fancy rigid body. The rigid body doesn’t have to be look alike the final model. Just think about the core movement of the object, a simple stick can become anything.
What kind of objects track well?
Simple, flat objects with fixed markers that won’t easily fall apart.
What different scenarios cause occlusion?
Missing markers.
Make a new rigid body with a prop in the room!
We tried out stick, chair, tennis ball, and a plate.
Can you make a person out of rigid bodies?
Originally I think I need to put the markers on myself. Later on, I realize a stick itself can become a person, depends on what kind of movement you want the person to make.
Can you act out a scene with only objects?
We made a first perspective shooting game.