New GCP test at Fairbanks International Airport

My plane had a flat tire on Sunday, so I took the opportunity to collect some ground control points (GCPs) around the ramp to compare to maps I had made there previously.  I was a bit concerned that there was perhaps some calibration issue with the system, given the Unalakleet GCPs showed a 20 cm standard deviation with my maps.  The airport results demonstrated that things were working just fine, since the airport GCPs showed a standard deviation of less than 2 cm.  This means that the high scatter in Unalakleet was likely due to real surface changing since the GCPs were acquired in 2011.  As we’ve found in nearly all other studies, at 95% confidence the precision of fodar is about +/- 4 cm.  Though harder to quantify, the spatial correlation was pretty much spot on as well, as the images below show.

pafa_131006_gcp_top
Here are the points I measured.  I made most of the measurements at intersections of cracks, the ends of yellow lines, or on the corners of numbers, so that I could assess any spatial misfits.

pafa_131006_gcp_oblique1
Here you can see the GCPs aligning with the corners of numbers and intersections of lines and cracks.  It doesn’t get any better than this really.

Here’s the data from the airport:

Point ID Easting (m) Northing (m) Difference (m)
PAFA0004 460120.51 7188366.51 -0.024
PAFA0005 460127.21 7188368.84 0.010
PAFA0006 460127.91 7188381.77 -0.020
PAFA0007 460148.14 7188394.66 -0.002
PAFA0008 460152.88 7188425.16 0.001
PAFA0009 460147.21 7188399.64 0.000
PAFA0010 460159.21 7188390.35 0.002
PAFA0011 460170.98 7188380.63 0.002
PAFA0012 460183.70 7188365.98 0.019
PAFA0013 460190.64 7188354.50 -0.011
PAFA0014 460168.72 7188327.26 -0.019
PAFA0015 460150.99 7188305.23 0.002
PAFA0016 460129.43 7188316.82 0.027
PAFA0017 460106.47 7188300.49 0.010
PAFA0018 460111.45 7188288.61 -0.033
PAFA0019 460130.78 7188280.25 -0.039
PAFA0020 460111.06 7188255.67 -0.004
PAFA0021 460090.10 7188249.21 0.007
PAFA0022 460075.04 7188261.37 0.016
PAFA0023 460061.76 7188272.05 -0.003
PAFA0024 460033.42 7188285.18 0.018
PAFA0025 460034.57 7188293.90 0.022
PAFA0026 460036.32 7188314.52 0.023
PAFA0027 460055.92 7188340.67 -0.004
PAFA0028 460073.34 7188362.21 0.018
PAFA0029 460082.80 7188354.62 -0.030
PAFA0030 460090.37 7188363.93 0.004
PAFA0031 460098.37 7188365.95 -0.007
PAFA0032 460103.33 7188364.36 0.014
PAFA0033 460106.20 7188364.26 -0.020
  Standard Deviation (m): 0.017

 

Note that the standard deviation is a metric of precision (that is, repeatability).   The data originally had a mean offset of about 12 cm, which is a metric of accuracy.

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