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PolyCAD

On initiating interactive drawing of surfaces, the cursor will change to a cross and indicate the Default Edit Plane. Left-Click to draw the first point and a rectangle on the Default Edit Plane will be drawn between the clicked point and the cursor. A subsequent Left-Click to complete the rectangle will complete the entity. Surfaces defined by control polygon will consist of four corner points and in the case of NURBS surfaces the initial order of both directions will be linear (2). Pressing Esc once the first point of the surface will cancel creation

The SnapToGrid and SnapToObject features can be used to provide additional assistance in the creation process and can be turned on or off from the status bar or from the PolyCAD Options Panel -> Manipulation Options. Points created using the SnapToObject will be project perpendicular from the snap location on to the Default Edit Plane.