Copy these files to: C:\Program Files\Corpscon6\Vertcon

Now for me, this is where it gets interesting, because even though you have
selected the customized grid file, it will not use this customized file in
the calculations, even though it say its using it in the header of the output

Here's where I exit the program and then start it up again...try it.

One way to insure that the correct model is being used, would be to visit the
NGS website (they only run the old model), and run a point through their
online version of the VertCon program thereby getting a second opinion: Click "Height Conversion"
on the left side. If you run a coordinate here, say 27 00 00.00 and 081 12
00.00, you will get a datum difference of -0.353 meters (-1.158 ft). Then
run this same position through CorpsCon, and see if you get this number or a
different conversion. I know this is not to most comforting nor scientific
system, but the other option is to wait until the next version of Corpscon is
released...December 21, 2012.

If you want to never have to think about this again, you could go to
C:\Program Files\Corpscon6\Vertcon on your hard drive, and rename the file
vertcone.94 to vertcone.94.old, and then rename vertcone.05 to
vertcone.94...that way the software will have no choice but to use the new
model file. I like to have both though, you you'll probably want to keep
that option.

Aside for a few select locations, I never really took a close look at the
difference between the two VertCon models....

I made a grid based roughly on the center of each of the 7.5min USGS Quad
maps for the eastern part of Florida. I then ran two sessions of CorpsCon,
first using the old, original 1994 Vertcon, then the 2005 CERP Geodetic
Control Network supported model. Each time, I used as an NGVD29 elevation of
0.00', and calculated the NAVD88 conversion. I then took the difference
between these two iterations and generated the surface model shown in the
attached files.

The file "Vertcon-Comparison.pdf" shows the difference between the results
that would be reached by using each of the two vertcon models. The range is
+0.15' west of Lake Okeechobee to -0.06' in Palm Beach county. Again, this
is the difference between the results obtained by each model. As an example
see file "VertCon-Comparison-Lake.pdf". At each data point are two text
annotations, the one in blue is the result from the original NOAA/NGS Vertcon
model, and the Red is from the USACE generated CERP-VertCon. One of the data
points in this file just at the west side of the lake has a red number of
-1.33, and a blue number of -1.18. What this means, is that for a published
NGVD29 elevation of 10.00', the original vertcon would return an NAVD88 of
8.82', while the new model would result in 8.67'...that's the 0.15'

-Jeff Navaille, U.S. Army Corps of Engineers


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