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That looks similar to the Ramsey County projection. In that case no
datum shift (mean grid shift files) are needed (although NAD83 vs
NAD83 HARN+ might be a small difference). What is different is
using a custom ellipsoid instead of GRS80. This is specified using
the a and b parameters to proj4 which define the semi-major and
semi-minor axes of the ellipsoid. These are given in a different
form in the Dakota County case as the semi-major axis and the
flattening as 6378421.989,298.2572133677353.<br>
<br>
My notes from the Ramsey County case follow:<br>
<br>
# MN Ramsey County Coordinates<br>
# From Mike Murphy (City Surveyer) 6/6/2006<br>
# From Mike Schadauer (MnDOT) 8/20/1996<br>
# Also from "Map Projections and Parameters" from
<a class="moz-txt-link-freetext" href="http://rocky.dot.state.mn.us">http://rocky.dot.state.mn.us</a> (c)2002 MnDOT accessed 6/5/2006<br>
# Conversion to from deg,min,sec to decimal degrees and Meters to
U.S. Survey Feet by Jim Klassen 6/5/2006<br>
# <br>
# Ramsey County Coordinate Definition<br>
#<br>
# Projection Lambert Conformal Conic based on North American Datum
83 with the 1986 correction<br>
# Note: while MnDOT uses the HARN (NAD83 (1996)) corrections, Ramsey
County does not. This amounts to<br>
# about a 7/10th foot difference across the county (Mike M.) Ramsey
Co. coordinates were designed to be<br>
# accurate to 1:50000 (Mike M.) Also note the unit is the U.S.
Survey Foot = 3937/1200 * meters.<br>
# <br>
# Parameters (verified matching from both Mike S. by way of Mike M.
and from the above web site): <br>
#<br>
# STANDARD PARALELLS<br>
#<br>
# North Standard Parallel = 45 deg 08 min 00 sec. =
45.1333333333333333<br>
# South Standard Parallel = 44 deg 53 min 00 sec. =
44.8333333333333333<br>
#<br>
# Longitude of Origin (Central Meridian) = -93 deg 23 min 00.0 sec.
= -93.383333333333333<br>
# Latitude Grid Origin = 44 deg 47 min 28 sec. = 44.791111111111<br>
# False Northing = 30480.0610 Meters = 100000 U.S. survey feet<br>
# False Easting = 152400.3048 Meters = 500000 U.S. survey feet<br>
#<br>
# To convert False Northing & Easting to U.S. survey feet
multiply<br>
# Meters by 3.280833333<br>
#<br>
# Semi Major Axis = 6378418.941 Meters (Equatorial) = GRS80
Semi-major-axis + ellipsoid_height = 6378137 + 281.941<br>
# Semi Minor Axis = 6357033.310 Meters (Polar)<br>
# Inverse Flatting 298.2572243<br>
# Inverse Flatting = Semi Major Axis / (Semi Major Axis - Semi Minor
Axis)<br>
# Semi Minor Axis = Semi Major Axis - (Semi Major Axis / Inverse
Flatting)<br>
<br>
<200068> +proj=lcc +lat_2=44.88333333333333
+lat_1=45.13333333333333 +lat_0=44.79111111111111
+lon_0=-93.38333333333334 +x_0=152400.3048 +y_0=30480.0610 +unit=sft
+to_meter=0.30480060960122 +a=6378418.941 +b=6357033.310 +no_defs
<><br>
<br>
So I would guess the Dakota County line would be:<br>
+proc=lcc +lat_2=44.91666666666666 +lat_1=44.51666666666667
+lat_0=44.47194444444445 +lon_0=-93.31666666666666 <br>
+x_0=152400.3048 +y_0=30480.0610 +unit=sft
+to_meter=0.30480060960122 +a=6378421.989 +b=6357036.347<br>
<br>
<div class="moz-cite-prefix">On 05/05/2014 04:18 PM, David Fawcett
wrote:<br>
</div>
<blockquote
cite="mid:CAF7K3b9FfseZxe8EzSLjvc4iekc0qfZN-Z8DcQoN0kCUyFXyjQ@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>
<div>I am projecting some of the new awesomely open Dakota
County spatial data from the Dakota County custom SRS to
EPSG 26915. <br>
<br>
</div>
It looks like a datum transform is in order, but I am having
a hard time coming up with one. Any suggestions?<br>
<br>
</div>
Here is the .prj file contents for the SRS:<br>
<br>
PROJCS["MN_Dakota_Lambert_Conformal_Conic",GEOGCS["GCS_MN_Dakota",DATUM["D_MN_Dakota",SPHEROID["MN_Dakota",6378421.989,298.2572133677353]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",500000.0],PARAMETER["False_Northing",100000.0],PARAMETER["Central_Meridian",-93.31666666666666],PARAMETER["Standard_Parallel_1",44.51666666666667],PARAMETER["Standard_Parallel_2",44.91666666666666],PARAMETER["Latitude_Of_Origin",44.47194444444445],UNIT["Foot_US",0.3048006096012192]]<br>
<br>
</div>
For reference, here is the .prj for 26915:<br>
<br>
PROJCS["NAD_1983_UTM_Zone_15N",GEOGCS["GCS_North_American_1983",DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-93],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["Meter",1]]<br>
<div><br>
<br>
</div>
<div>It looks like they use the same spheroid.<br>
<br>
</div>
<div>David.<br>
</div>
</div>
<br>
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