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Extraction by Digital Photography   

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Preparatory Phase
P3DM supplies
Assembling the "blank"
Depicting info
Transposing info
Data Extraction
Digital Photography
On-screen Digitizing
GIS processing
Map Production (1)
Map Production (2)
Data validation
Handing Over
P3DM and PM&E

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P3DM: Guiding Principles and Applications

 

To reduce radial and relief displacements, Parallel Camera Movement shooting is recommended. This technique involves moving the camera at a set distance from an object, such as the 3-D Model, to capture it in sections. Each picture should be shot perpendicularly to the model surface.

Canon PowerShot G2Place a high-resolution digital camera on a tripod at 4-m distance from the base of the tilted model. Draw lines perpendicular to the model’s horizontal plane on the floor at 40 cm intervals. Add a reference line at the end of the orthogonal lines to serve as guide in moving the camera from one position to the following one. Adjust the focal length setting to capture an area of approximately 40 cm x 50 cm. Extraction of data from the terrain model by the use of digital photographySet the camera to the maximum resolution (e.g. 2272 x 1704 pixels) and compression capacity. This setting will provide high quality images of approximately 2 MB each.

The number of images that can be stored on the Compact Flashcard depends on its storage capacity. A standard CF-32M card may contain up to 14 images shot at these high quality settings.

To cover the entire area of a model measuring 2.5 x 1.2 meters, shoot at least 24 pictures. Intermediate downloads to a separate storage device may therefore be necessary.

Position the camera with the use of a plumb line exactly above the intersection of the orthogonal and the reference lines. The height of the camera above ground is chosen and has to be constant throughout the first passage.

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