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' |
|
