Designing Immersive Display Setup

Apr 13, 2014

Designing Immersive Display Setup

Designing an Immersive multi-projector projection setup is a very complicated task. A dozen of questions have to be answered to make a decision for the projection screen and the projectors.

  • The type of the screen (cylinder, dome, etc..)
  • The radius and the height of the screen.
  • The number of projectors needed to cover the screen.
  • The projection resolution and aspect ratio
  • The needed projector throw ratio
  • Projector uniformity on the screen (how image is distorted on the screen)
  • The projector image utilization (how much projector image falls outside of the screen)
  • What will happen if you have an object between the projector and the screen. How and where the object will drop shadow on the screen.
  • ….

One of the most often mistakes that one can be made is just jump into buying the projectors and building the screens, just to find out that the setup is not optimal or even worse, the setup is not working. 
A careful plan and design phase is needed creating a multi-projector setup on a non-planar projection surfaces. Usually, several iteration steps are needed that include the following steps: plan, design, evaluate, decide, plan, decide, evaluate, …. It is all about making rational choices and compromises based on weighted tradeoffs. 
We at Fly Elise-ng offer users the program Immersive Designer PRO to design and evaluate their setups themselves. Users need to understand the basic principles of projection on irregular surfaces and have to be prepared to make compromises in their choices for screen and projectors. 
So, lets walk through the several “plan, design, evaluate, decide” steps needed to come up to the most optimal multi-projector setup. 
One of the first decisions that one has to make is the type and the dimensions of the screen. Fixing one of the variables in the setup will make us focus and evaluate how other variables (ex. projectors) will influence and fit into the setup. Lets say, we would like to create a cylindrical screen projection with screen height of 2.0 meters, radius of 2.3 meters and screen angle of 220 deg. Those seem common dimension for a simulation setups. 

Now, the question arises: What type of projector can be used, who many projectors and where to position the projectors to the desired screen coverage and projectors overlap. Immersive Designer PRO comes with a database with more than 5000 projector models from the most of the projectors manufacturers. Choosing the projector is one of the most important choices that we need to make. Projectors are characterized by multiple factors: resolution, brightness, etc. One of the most important factors that determines the projector coverage on the screen is the projector throw ratio. This factor determines the size of the projected image based on the projector distance from the projection surface. Another factor is the projector vertical offset. This offset determines the vertical position of the projectors. 
So, lets use Immersive Designer PRO and select one projector available in the database. BenQ MX720 is a 1024×768 projector with a throw ratio of 1.93 and aspect ratio of 4:3. Lets position this in the center of the projection and evaluate the projected image on the screen. 

We can see that the image this projector produces on the screen is way too small to be able to cover the screen with 3 projectors. In order to be able to cover the screen vertically, this projector has to be put on a 5.7 meters distance from the screen. At this distance the projected image will lose the required brightness. 

It is clear that we will need a projector with much smaller throw ratio. Let’s select BenQ MX822ST which has a throw ratio of 0.65. We can see that this projector positioned on 2.3 meters distance of the screen will cover the screen vertically. 

However, already 20% of the projected image is outside of the lower edge of the screen and the width of the projected image is not enough to cover the projection screen with 3 projectors including the overlap. 

We can see that we need a projector with different (wider) aspect ratio to be able to cover the whole screen. Let’s select BenQ LW61ST with resolution of 1280×800, throw ratio of 0.52 and aspect ratio of 16:10. This projector gives us a good image from a distance of 2.3 meters from the screen. This projector is a good basis for the next steps. 

Let’s now add 2 more projectors of the same type: the left and the right projector and try to position them in such a way that the projector have approximately 10% to 15% overlap at the edges. This overlap is needed for soft-edge blending. Soft-edge blending will be covered in one of the future blog articles. 
We can see that when we mount the 3 projectors the adjust the projectors rotations to achieve the desired overlap we are faced with 2 consequences: The combined projected image does not cover the whole height of the screen, and also that the projected image does not cover the desired screen angle of 220 deg. At this moment we will need to make a compromise and chose either a smaller screen size and angle or go for another type of projector. Selecting a smaller screen size we can end up with a screen angle of 180 deg and screen height of 1.8 meters.

In this case we will assume that the screen angle of 220 deg is very important for our setup. We will try to use other projector types and evaluate if we can still achieve this. Let’s select projector type BenQ MP780 ST+ with resolution of 1280×800, throw ratio of 0.46. 

When the projectors positioned to achieve the desired overlap we can see that we are approaching very closely our goal for the projection screen size. However, still not the whole projection screen is covered in width and height. At this moment we can compromise on the screen height and angle without diverging too much from our initial goal. In this case a screen height of 1.8 meters and angle of 210 deg will match the projectors coverage

When we have to position a cockpit or other objects in the projection setup between the projector and the projection screen, these objects will cast shadows from the projection light of one or more projectors on the screen. Also the projection light can shine on the object surface. In Immersive Designer PRO we can import a 3D model from a number of supported 3D object formats and evaluate the impact of the object position on the projection. In this case we can chose for a mockup of a sport car that will host the driver. If we position the car closer to the screen, a shadow can be observed on the screen from the center projector caused by the car engine hood. In this setup the left and the center projector fortunately cast no shadows. 

In order to minimise the shadow we will move the car mockup to the back. The eyepoint of the driver is still close to the focus point of the screen. 

Part of the projected image is casted on the engine hood. This part of the image can be masked late using Immersive Display PRO masking features. 
With Immersive Designer PRO you can do all those tasks and choices and immediately and visualize and evaluate the effects in real-time. You will need to invest some time in order to design your setup and make sure that the design is based on the right choices taken during the design process. 
After the design is finished we can build the projection setup being sure that the built setup will exactly resemble the designed setup. After that we can use Immersive Display PRO and optionally Immersive Calibration PRO to calibrate the projection for seamless image and soft edge blending from all projectors on the screen.

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