The Perspective Grid parameters are stored in the document dictionary. Here are the keys and their types:
PerspectiveGrid_HorizonHeight [Real]
PerspectiveGrid_FloorRed [Integer]
PerspectiveGrid_LeftBlue [Integer]
PerspectiveGrid_RightPlaneVisibilityState [Integer]
PerspectiveGrid_RelativeFloorVanishingPoint [Point]
PerspectiveGrid_RightPlaneCellExtent [Point]
PerspectiveGrid_LeftPlaneTopPoint [Point]
PerspectiveGrid_LeftVanishingPoint [Point]
PerspectiveGrid_RightPlaneTopPoint [Point]
PerspectiveGrid_RulerOriginIndexSecond [Integer]
PerspectiveGrid_LeftPlaneBottomPoint [Point]
PerspectiveGrid_LeftPlaneCellExtent [Point]
PerspectiveGrid_RightPlaneBottomPoint [Point]
PerspectiveGrid_RulerOriginIndexFirst [Integer]
PerspectiveGrid_RightVanishingPoint [Point]
PerspectiveGrid_FloorPlaneVisibilityState [Integer]
PerspectiveGrid_LeftPlaneVisibilityState [Integer]
PerspectiveGrid_FloorOffset [Real]
PerspectiveGrid_FloorGreen [Integer]
PerspectiveGrid_LeftFaceAngle [Real]
PerspectiveGrid_LeftGreen [Integer]
PerspectiveGrid_LeftRed [Integer]
PerspectiveGrid_Unit [Integer]
PerspectiveGrid_StationPoint [Point]
PerspectiveGrid_ViewingDistance [Real]
PerspectiveGrid_RightExtent [Real]
PerspectiveGrid_Scale [Point]
PerspectiveGrid_Type [Integer]
PerspectiveGrid_RightRed [Integer]
PerspectiveGrid_RightBlue [Integer]
PerspectiveGrid_LeftExtent [Real]
PerspectiveGrid_FloorBlue [Integer]
PerspectiveGrid_RightOpacity [Real]
PerspectiveGrid_RightGreen [Integer]
PerspectiveGrid_RightFaceAngle [Real]
PerspectiveGrid_LeftOpacity [Real]
PerspectiveGrid_CellSize [Real]
PerspectiveGrid_FloorOpacity [Real]
PerspectiveGrid_CellCount [Real]