< Point Co.

LIMITATIONS OF PHOTOGRAMMETRY

First Order Stereo Plotter has an accuracy of the reading of 5 microns or better.
PoinT Co. owns and operates Zeiss – IMA first order analytical plotter with RMSE on a grid plate of 2 microns.

Aerial cameras used in photogrammetry should be calibrates by USGS. Accuracy of the calibration is considered to be 5 microns.

Adding distortion of the film and diapositives, and stereo plotter operator's error, it is considered that maximum achievable positional accuracy utilizing photogrammetry is 7-10 microns.

Vertical accuracy is in a direct function of a flight height. For the first order stereo plotters vertical accuracy is expected to be between 7/100,000 (seven parts in a hundred thousand) and 1/10,000 (one part in ten thousand) of a flight height. Minimum flight height for the fixed wing aircraft is 1000 ft above the ground. With the typical 6" camera (153 mm focal length) it corresponds to a photo scale of 1"=167' (1:2000).

MAXIMUM ACCURACY

Photo Scale

1"=

10 microns
horizontal
accuracy
(feet)
flight height/10000
2500 C factor
vertical accuracy
(feet)
167' 0.06 0.10
200' 0.08 0.12
250' 0.10 0.15
300' 0.12 0.18
350' 0.14 0.21
400' 0.16 0.24
500' 0.20 0.30
600' 0.24 0.36
700' 0.28 0.42
800' 0.32 0.48
1000' 0.40 0.60
1200' 0.46 0.72
1500' 0.58 0.90
1800' 0.72 1.10
2000' 0.78 1.20

PoinT Co. optimizes photo scale depending on client's specifications, accuracy requirements and level of detail to be mapped.

TYPICAL PHOTO SCALES

Map Scale / Contour Interval

Photo Scale

1"=20' / 1' CI 1"=167' - 1"=250'
1"=40' /1' CI 1"=250' - 1"=350'
1"=40' /2' CI 1"=300' - 1"=500'
1"=100' /2' CI 1"=500' - 1"=800'