A line or boundary in a RatEnvironment. The visible option applies to the rat, and can be used, for example, to mark the edge of a platform (visible=false), which is not seen but which cannot be crossed. The solid field specifies whether the boundary is can be crossed (solid=no), looked over but not crossed (solid=semi), or not breached at all (solid=yes). Since ratlab is two dimensional, "looked over" here means that the rat is able to stick its nose through and see what is on hte other side, but not get there.
The projectOnto field marks a particular line for 1-D position measurement of the Rat. Note that each environment can only have one such line. The 2-D position of hte rat is projected onto the nearest segment of the chosen line, producing a single value - the distance ofthe projected point from the beginning of the line, measured along the line. Lines for projection may have a single straight segment, simply indicating an axis through the environmnet, or may have a complicated shape to measure the rat's progrsss along a particular path. The output of the measurement is sent to the spike analysis component for display or correlation with other measurements.