FlyVR - virtual reality engine

FlyVR is a virtual reality engine built on ROS and OpenSceneGraph. It manages multi-computer realtime tracking and display with the goal of being useful for scientific studies of vision.

FlyVR pipeline overview


Theory of operation

A moving observer has a pose within a global coordinate frame. Objects within the global frame may also move or be updated (e.g. a moving grating). Six camera views with a fixed relationship to the observer are used to build a cube map, showing the scene surrounding the observer without regard to the projection surface.

This cube map is then projected onto a 3D shape model of the display surface. From there, this image is warped to the physical display output.

flyvr nodes

display_server - the FlyVR display server

The FlyVR display server node runs locally on the computer(s) connected to the physical display. During a typical experiment, it will be running an experiment plugin. Each experiment plugin updates the graphics engine on the basis of the fly’s current position. Given the scenegraph and the calibrated screen layout, the node will compute the images shown on the projectors. - FlyVR viewport definer

Runs a GUI program that allows the user to interactively define the viewports for all connected projectors.


Display Coordinates - the native pixel indices on a physical display. These are 2D.

World Coordinates - the 3D coordinates in lab space of physical (or simulated) points. (May also be represented as a 4D homogeneous vector x,y,z,w with nonzero w.)

Physical Display - a physical device capable of emitting a large, rectangluar block of pixels. It has display coordinates - the 2D locations of each pixel. (A physical display does not have world coordinates used for the VR mathematics. On the other hand, A virtual display does have world coordinates.)

Virtual Display - a model of a physical display which relates world coordinates to display coordinates. The model consists of a linear pinhole projection model, a non-linear warping model for lens distortions, viewport used to clip valid display coordinates, 3D display surface shape in world coordinates, and luminance masking/blending. Note that a physical display can have multiple virtual displays, for example, if a projector shines onto mirrors that effectively create multiple projections.

Viewport - vertices of polygon defining projection region in display coordinates (x0,y0,x1,y1,...). It is used to limit the region of the physical display used to illuminate a surface. (The FlyVR Viewport corresponds to a 2D polygon onto which the image of the projection screen is shown.)

Display Surface - a physical, 2D manifold in 3D space which is illuminated by a physical display (either by projection or direct illumination like an LCD screen).