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Question

A question regarding digital cameras vs analog. Would flying height for high accuracy large scale mapping with a digital camera with a focal length of 100.5mm compared to a traditional frame camera with a focal length of 152mm relate as a ratio? That that is for example… (550m AGL)/(152mm) Frame Camera = (364m AGL)/(100.5mm) Digital Camera …or is it maybe not that simple because of the higher resolution of the digital camera?

Answer

Generally the digital cameras have a smaller pixel than the scanned images. However, the pixels size does not dictate the accuracy. The smaller focal lengths lead to a weaker geometry. So, in the case of large scale high accuracy requirements you would need to fly lower than in the past. In the case of medium to small scale (low accuracy) projects you are able to fly higher due to the finer resolution/pixel size creating a better resolution for detail to be observed.

In ISAT we use .2 of a pixel as the rule of thumb to shoot for with the relative precision at the photo scale. The Check Point RMS is used for the Object solutions to determine the precision of the adjustment. If this meets the National Map Accuracy guidelines or the Corp of Engineer guidelines that is what you are shooting for generally. If you are delivering contours the AT had to be good to about a quarter of the contour for good results. The raw imagery should be finer than the scaled pixel ortho resolution as it does no good to down sample only creating a larger file size.

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