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Laser Sketch

    Laser Sketch is an ESRI ArcMap/ArcScene extension that enables the real-time mapping of points from a laser range finder or a total station to their correct position on a photograph. Laser Sketch uses the camera lens distortion parameters to correctly place the point measured by the laser instrument. The lens distortion parameters can be obtained using free ware programs or commercial programs such as MatLab_® and Photo Modeler_®. The distortion parameters need to be measured only once for each camera/lens combination. The parameters are saved in the Laser Sketch directory on the laptop. The laptop is connected to a laser instrument that has a traverse and elevation capability. We currently have drivers for some Topcon_® and some Laser Atlanta_® instruments.

    A photograph of the target area is taken with the camera and loaded into Laser Sketch.  Four tiepoints are selected between the target and the photograph.  A graphic marker is placed in the photograph and the XYZ location of the point is measured with the laser instrument.  After the four tiepoints are captured, the 3D to 2D transformation parameters that relate the target to the photograph are calculated.  All subsequent points that are shot with the laser instrument are plotted on the photograph in their approximately correct position.  Accuracy of less than two pixels in placement of the points is easily achieved with a total station. 

    The resulting points can be displayed in 3D mode in an ArcScene window in Laser Sketch. The points can be converted into 3D polylines and 3D polygons. For geological outcrops, the point based tools in GeoAnalysis Tools can be used to analyze the orientations of the features which have been sketched.
 

Electric tower created from digitized 3D points using Topcon Total Station and Laser Sketch program

• One time distortion characterization of camera and lenses. 
• Photograph target
• Load photograph in Laser Sketch (ArcMap/ArcScene)
• Identify a tiepoint in Laser Sketch with graphic marker and shoot XYZ location with laser/total station
• Repeat until at least four points have been selected
• Calculate 3D => 2D transformation parameters, repeat process if residuals are unsatisfactory
• All subsequent XYZ points that are shot will be plotted on the photograph in real-time.  Points can be named and attributed at time of capture

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