[Mapserver-users] GPS data Projection

[Gerry Creager N5JXS]

Several things to consider.

1.  What datum is the GPS configured to display
1a.  When so configured, does it also output the data in that datum from 
its memory (this is not as obvious as it seems with some consumer-grade 
GPS receivers).
2.  You can generally use WGS84 data (default GPS datum) on top of NAD83 
  maps. You may see a small error associated with the differences 
between the 2 datums, but it should be of little importance unless your 
data are already of high accuracy... say, at the centimeter level.

You will have to add a reference for the mapfile to the correct 
datum/projection in use in a Projection section (init=epsg:26915) and 
similarly, in the GPS layer, a Projection section referencing 
'init=epsg:4326' as well as identifying, in the GPS layer, units as degrees.

I've probably missed something, but it's late.

gerry

Changqing Zhou wrote:
> HI, I would greatly appreaciate your help on a projection question:
> 
> How do I display gps data in lat-long point format on top of the following
> MNDOT base road shapefile? How to project the GPS data to the road map system?
> 
> (http://www.dot.state.mn.us/tda/basemap/metadata/Roads.htm)
> 
> Horizontal Coordinate Scheme  UTM
> Ellipsoid  GRS80
> Horizontal Datum  NAD83
> Horizontal Units  Meters
> 
> Below is my simplified maplefile. Note I do not use any projections:
> 
> MAP
>   NAME           Hennepin County
>   IMAGETYPE      png
>   #EXTENT         201621.496941 -294488.285333 1425518.020722
> 498254.511514 # LAEA
>   EXTENT		439000 4960000 487000 5010000 #from arcview
>   #EXTENT         -97.5 41.619778 -82.122902 49.38562 # Geographic
>   SIZE           800 600
>   SHAPEPATH      "data"
>   SYMBOLSET      "symbols/symbols35.sym"
>   FONTSET        "fonts/fonts.list"
> 
>   WEB
>     TEMPLATE  'hennepinRoads.html'
>     IMAGEPATH '/ApacheGroup/Apache2/htdocs/tmp/'
>     IMAGEURL  '/tmp/'
>   END
> 
>   PROJECTION
>   # This is Lambert Azimuthal Equal-Area projection for the
>   # Continental U.S.
>   #  "proj=laea"
>   #  "ellps=clrk66"
>   #  "lat_0=45"
>   #  "lon_0=-100"
>   #
>   # Alternatively, you can specify an EPSG code.
>   # This is the EPSG code for
>   # Lambert Azimuthal Equal-Area projection for the U.S.
>   #"init=epsg:2163"
>   #
>   END
> 
> LAYER # Hennepin Road layer begins here
>   NAME         hennepin_line
>   DATA         hennepinm
>   STATUS       DEFAULT
>   TYPE         LINE
> 
> #  PROJECTION
> #    "init=epsg:4326"
> #  END
> 
>   CLASSITEM "Code"
>   CLASS
>       EXPRESSION '01'
>       COLOR 0 0 255
>   END
>   CLASS
>       EXPRESSION '02'
>       COLOR 0 0 255
>   END
>   CLASS
>       EXPRESSION '03'
>       COLOR 255 0 0
>   END
>   CLASS
>       EXPRESSION '04'
>       COLOR 0 255 255
>   END
> 
> END # Hennepin Roads layer ends here
> 
> 
>   # End of LAYER DEFINITIONS -------------------------------
> 
> END # end of map file
> 
> 
> Thanks,
> 
> Changqing
> 
> 
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-- 
Gerry Creager -- gerry.creager at tamu.edu
Network Engineering -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Page: 979.228.0173
Office: 903A Eller Bldg, TAMU, College Station, TX 77843