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Taking Photographs

Taking Photographs

Almost any photograph of a flat surface can be used for rectification. Of course, the quality of the resulting rectified image will be directly proportional to the quality of the source image and there are a few additional parameters over and above those common to all photographs (focus, lighting, stability, etc.) that will have an effect.

The photo should be taken from as close to right angles to the surface to be rectified as is possible. This is not to say that seriously oblique images cannot be used, only that the quality of the result will be better if the software does not have to make huge adjustments.

The points to be measured should be clearly visible. This requirement may conflict with the need to show detail in the areas you cannot measure but this can be got around by taking multiple photographs - one for identifying the measurement points, and others exposed for detail in other areas.

If more than one photo is taken from a single location (i.e. using a tripod) and with the same orientation and focal length the point mapping files will be interchangeable using the alternate point file feature of ASRix.

An extreme example of this would be the archaeological practice of placing a grid of a known spacing over the area to be photographed and taking two photos - one with the grid in place and one without. The image with the grid can be easily rectified and the resulting point file can be used on the image without the grid to get a rectified image of the artifacts.

Targets or scales on walls can also be used in this way. One simple approach is described in the TAPES example in the samples.

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Generated by: CART
(Thu Sep 20 17:56:23 2007 )