<div dir="ltr">Jim, David,<div><br></div><div>You can also specify the flattening directly as a parameter instead of the minor axis I believe.</div><div><br></div><div>In any case, the easiest way to generate it for me is to use QGIS and add a shapefile with that prj file. If you then go to settings/Custom CRS, you can find the projection with all the parameters.</div>
<div><br></div><div>Using a shapefile downloaded from Dakota Co, I got:</div><div>
<p style="margin:0px">+proj=lcc +lat_1=44.51666666666667 +lat_2=44.91666666666666 +lat_0=44.47194444444445 +lon_0=-93.31666666666666 +x_0=152400.3048006096 +y_0=30480.06096012192 +a=6378421.989 +b=6357036.347 +units=us-ft +no_defs</p>
<p style="margin:0px"><br></p><p style="margin:0px">which I believe confirms Jim's answer, save for irrelevant parameter ordering.</p><p style="margin:0px"><br></p><p style="margin:0px">using the flattening:</p><p style="margin:0px">
+proj=lcc +lat_1=44.51666666666667 +lat_2=44.91666666666666 +lat_0=44.47194444444445 +lon_0=-93.31666666666666 +x_0=152400.3048006096 +y_0=30480.06096012192 +a=6378421.989 +rf=<span style="font-family:arial,sans-serif;font-size:13px">298.2572133677353</span> +units=us-ft +no_defs</p>
<p style="margin:0px"><br></p><p style="margin:0px">Philippe</p><p style="margin:0px"><br></p></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, May 5, 2014 at 7:15 PM, Jim Klassen <span dir="ltr"><<a href="mailto:klassen.js@gmail.com" target="_blank">klassen.js@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
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 href="http://rocky.dot.state.mn.us" target="_blank">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<div><div class="h5"><br>
<br>
<div>On 05/05/2014 04:18 PM, David Fawcett
wrote:<br>
</div>
</div></div><blockquote type="cite"><div><div class="h5">
<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>
<fieldset></fieldset>
<br>
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