Multi View [2007.01.15]

Introduction
Enabling a map for MultiView
Using the MultiView
Configuration
Limitations

Introduction

The USARSim client allows to see only from the camera(s) of one robot at the time. To overcome this limitation a special extension, called MultiView, was developed. This extension is not new, it's several months that it is included in the simulator. As no documentation still exists on how to use it I'm writing this short guide.

Enabling a map for MultiView

In order to enable the MultiView you have to add a special object into the map. You must use the Unreal Editor to do that. Open your map in the Unreal Editor (I will use the Soccer map as an example):

Fig.1

Click on the pawn button as illustrated. It will open the Actor Classes window:

Fig.2

In the tree view search for MultiView and select it. The path to it is Actor/Pawn/MultiView. Now right click somewhere in the map (in the perspective view) and select "Add MultiView Here":

Fig.3

Close the Actor Classes view. The following box should have appeared in the map:

Fig.4

You can place it wherever you want, for example near the ceiling so to hide it from robot cameras. Now click on the rebuild button to rebuild the map:

Fig.5

and save it.

Using the MultiView

With MultiView you can capture the camera view from many robots at the same time as illustrated in the following picture:

Fig.6

Just keep left clicking until you find it. You can write your own capturing image server, extract the images of each robot and send them to respective clients, as illustrated here:

Fig.7

Otherwise you can use the image server that comes with USARSim and split the camera images at client side.

MultiView can also render stereo cameras in each subview. To do so you have to add this function to your robot class (subclassed from KRobot):

//(Called by KRobot Tick function)
//Stereo vision when viewing from multiview robot camera
simulated function SyncMultiView()
{
    if(ViewManager != none)
    {
        if(isStereo)
            ViewManager.UpdateView(ViewNum, myCamera.Location, myCamera.Rotation,
                                   CameraZoom, true, uuStereoSpacing);
        else
            ViewManager.UpdateView(ViewNum, myCamera.Location, myCamera.Rotation,
                                   CameraZoom, false);
	}
}

where:

• isStereo : is a boolean variable you can use to enable/disable stereo rendering. Obviously, if you plan to always use stereo camera then you can delete the if(isStereo) statement. You can declare this variable config so to be able to set its value inside USARBot.ini file.
• uuStereoSpacing : is a vector that defines the (eye to eye)/2 spacing in unreal units. 1m = 250 unreal units, so you can make a manual conversion. Otherwise you can use the converter to automatically convert a stereo spacing parameter expressed in meters to unreal units. To do so you have to add the following function in you robot class:

simulated function ConvertParam(USARConverter converter)
{
    Super.ConvertParam(converter);
    if(converter!=None)
    {
        uuStereoSpacing = converter.LengthVectorToUU(stereoSpacing);
    }
    else
    {
        uuStereoSpacing = stereoSpacing;
    }
}

where:

• stereoSpacing : is a vector that defines the (eye to eye)/2 spacing in meters.

You can define a vector in defaultproperties like this:

defaultproperties
{
    ...
    stereoSpacing=(Y=0.05) //5 cm: (eye to eye)/2 spacing in meter
    ...
}

Configuration

You can configure the MultiView in the USARBot.ini file. You will find the [USARBot.MultiView] section that contains the following parameters:

• CameraNum : maximum number of cameras that can be drawn at the same time.
• WideMode : if 0 the MultiView will split the screen using a box pattern. You can see in Fig.7 the pattern used for 4 cameras. If > 0 then the MultiView will use that number of columns before adding a raw. In Fig.6 you can see an example with WideMode=4.
• CameraXres : X resolution of robot camera. The final resolution of the camera subview will be <= CameraXres. If the overall resolution of camera subviews is larger than what can fit in the USARSim client, they will be scaled down to fit the screen. If for example you use 4 cameras in WideMode=4, each 200 pixel wide, and the USARSim client resolution is 640x480, each camera width will be scaled down to 160 pixel. But if you set WideMode=0 a different patter is used and the full camera resolution (200 pixel) will be used.
• CameraYres : Y resolution of robot camera. Same as above but for Y axis. In any case the aspect ratio (CameraXres/CameraYres) will be preserved. That means that a change in resolution will always affect both X and Y.
• IsCameraLocked : Don't consider this for now and leave it to false. It can be used with zone optimization to speed up subview rendering.

Limitations

I can think of two important limitations:

1. MultiView supports only one camera (can be stereo) per robot. So, if you have a robot that mounts more than one camera (like Talon) you will see only from its first camera.
2. More cameras you use (same as saying: more robots you use) smaller will be the subviews. This can, or can not be a problem. Depends on the specific application.