[TCMUG] Datum Transform Dakota Cnty => NAD83?

Mon May 5 20:04:53 PDT 2014

Jim, David,

You can also specify the flattening directly as a parameter instead of the
minor axis I believe.

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.

Using a shapefile downloaded from Dakota Co, I got:

+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

which I believe confirms Jim's answer, save for irrelevant parameter
ordering.

using the flattening:

+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=298.2572133677353 +units=us-ft
+no_defs

Philippe

On Mon, May 5, 2014 at 7:15 PM, Jim Klassen <klassen.js at gmail.com> wrote:

>  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.
>
> My notes from the Ramsey County case follow:
>
> # MN Ramsey County Coordinates
> # From Mike Murphy (City Surveyer) 6/6/2006
> # From Mike Schadauer (MnDOT) 8/20/1996
> # Also from "Map Projections and Parameters" from
> http://rocky.dot.state.mn.us (c)2002 MnDOT accessed 6/5/2006
> # Conversion to from deg,min,sec to decimal degrees and Meters to U.S.
> Survey Feet by Jim Klassen 6/5/2006
> #
> # Ramsey County Coordinate Definition
> #
> # Projection Lambert Conformal Conic based on North American Datum 83 with
> the 1986 correction
> # Note: while MnDOT uses the HARN (NAD83 (1996)) corrections, Ramsey
> County does not. This amounts to
> # about a 7/10th foot difference across the county (Mike M.) Ramsey Co.
> coordinates were designed to be
> # accurate to 1:50000 (Mike M.) Also note the unit is the U.S. Survey Foot
> = 3937/1200 * meters.
> #
> # Parameters (verified matching from both Mike S. by way of Mike M. and
> from the above web site):
> #
> # STANDARD PARALELLS
> #
> # North Standard Parallel = 45 deg 08 min 00 sec. = 45.1333333333333333
> # South Standard Parallel = 44 deg 53 min 00 sec. = 44.8333333333333333
> #
> # Longitude of Origin (Central Meridian) = -93 deg 23 min 00.0 sec. =
> -93.383333333333333
> # Latitude Grid Origin = 44 deg 47 min 28 sec. = 44.791111111111
> # False Northing = 30480.0610 Meters = 100000 U.S. survey feet
> # False Easting = 152400.3048 Meters = 500000 U.S. survey feet
> #
> # To convert False Northing & Easting to U.S. survey feet multiply
> #   Meters by 3.280833333
> #
> # Semi Major Axis = 6378418.941 Meters (Equatorial) = GRS80
> Semi-major-axis + ellipsoid_height = 6378137 + 281.941
> # Semi Minor Axis = 6357033.310 Meters (Polar)
> # Inverse Flatting 298.2572243
> # Inverse Flatting = Semi Major Axis / (Semi Major Axis - Semi Minor Axis)
> #  Semi Minor Axis = Semi Major Axis - (Semi Major Axis / Inverse Flatting)
>
> <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 <>
>
> So I would guess the Dakota County line would be:
> +proc=lcc +lat_2=44.91666666666666 +lat_1=44.51666666666667
> +lat_0=44.47194444444445 +lon_0=-93.31666666666666
> +x_0=152400.3048 +y_0=30480.0610 +unit=sft +to_meter=0.30480060960122
> +a=6378421.989 +b=6357036.347
>
>
> On 05/05/2014 04:18 PM, David Fawcett wrote:
>
>   I am projecting some of the new awesomely open Dakota County spatial
> data from the Dakota County custom SRS to EPSG 26915.
>
>  It looks like a datum transform is in order, but I am having a hard time
> coming up with one.  Any suggestions?
>
>  Here is the .prj file contents for the SRS:
>
>
> 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]]
>
>  For reference, here is the .prj for 26915:
>
>
> 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]]
>
>
>  It looks like they use the same spheroid.
>
>  David.
>
>
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