MEASURING IN VANISHING POINT
In Vanishing Point, you can take advantage of the new measurement tools by measuring something in three dimensions. You simply grab the Measure tool (R) and click between two points. Then in the top of the dialog, enter an establishing value in the Length field. This value will be what all other measurements will be based on. You can then render these measurements to Photoshop from Vanishing Point's flyout menu. TIP: You may want to use a blank layer before going into Vanishing Point because when measurements are rendered, they appear on the currently active layer.