EPSG code for...

[Dean Mikkelsen]

Hi Chris,

NAD83 has no relation to Clarke 1866. NAD83 is defined on GRS80/WGS84 - which are totally different ellipsoids from Clarke 1866. There will be no EPSG code for this. 

The fix may be quite simple actually now. Clarke 1866 defines NAD27, therefore both Shapefiles may be in NAD27, even though one says it is NAD83. 

Try assuming that the 2nd Shape file is NAD27 for the datum. Use the EPSG code 26711. 

The other alternative is assume both are NAD83/WGS84 (difference is neglible), but make sure that you define the ellipsoid of the 2nd shape file to be WGS84, not using any EPSG codes in setting up the map projection and datum. Then reproject the first one as NAD83/WGS84.

Let's see what happens.

Dean



----- Original Message -----
From: "Christopher R. Thorne" <christhorne at SYMPATICO.CA>
Date: Tuesday, June 14, 2005 7:36 am
Subject: Re: [UMN_MAPSERVER-USERS] EPSG code for...

> Hello me again,
> I finally tracked down the metadata for the data that was given to 
> me 
> with the strange projection. Well it gets stranger. Here is what I 
> found. I have two shape files of the Los Angeles county
> 
> 1st shape file :
> ----------------
> Datum:NAD27
> Units: Meters
> Ellipsoid:Clark 1866
> Projection: UTM, Zone 11
> 
>  * Possible EPSG codes found:
> 
> # NAD27(76) / MTM zone 11
> <2020> +proj=tmerc +lat_0=0 +lon_0=-82.5 +k=0.999900 +x_0=304800 
> +y_0=0 
> +ellps=clrk66 +units=m +no_defs  no_defs <>
> 
> # NAD27 / UTM zone 11N
> <26711> +proj=utm +zone=11 +ellps=clrk66 +datum=NAD27 +units=m 
> +no_defs 
>  no_defs <>
> 
> 2nd shape file:
> 
> Datum:NAD83
> Units: Meters
> Ellipsoid:Clark 1866
> Projection: UTM, Zone 11
> 
>   * Possible EPSG Codes found:
> 
>   NONE FOUND.....
> 
> This makes me think that NAD83 with a Clark 1866 Ellipsoid is not 
> a 
> valid projection. Am I on the right trake of thinking or is there 
> actually an EPSG code with:
> 
> <????> +proj=utm +zone=11 +ellps=clrk66 +datum=NAD83 +units=m 
> +no_defs 
> no_defs <>
> 
> Comments?
> Chris
> 
> Christopher R. Thorne wrote:
> > Hello Dean,
> > 
> > Dean C. Mikkelsen wrote:
> > 
> >> Hi Chris,
> >>
> >> Take a look at the following web-page.
> >> I am leaning towards a problem now in defining which State Plane
> >> Co-ordinate System is being used. i.e. one of the ones we are 
> using is
> >> wrong - we may actually be north or south of the current one. 
> Now the
> >> trick is to determine which one. A note to other readers 
> epsg:4326 is
> >> WGS84.
> >>
> >> Did you try reprojecting the NAD27 Layer with the NAD83 
> definition? 
> > 
> > 
> > Yes I did that and the layers switched positions.
> > 
> > Or
> > 
> >> with epsg:4326? What happens?
> >>
> > with setting the projection to the lat/long layers, they are not 
> found 
> > in outer space, not within the world extent.
> > 
> >> http://www.wadetrim.com/resources/articles/sblocks.htm
> > 
> > 
> > Thanks for the good reference. The reason why I got into this 
> situation 
> > was because I am four steps removed from the data provider. I 
> only 
> > managed to get the information that you already know and I was 
> hoping 
> > the information was correct. The other problem was that I was 
> not sure 
> > how to identify the issues, confidently. If not I will 
> definitely push 
> > for more information.
> > 
> > Cheers and thanks again,
> > Chris
> > 
> 
> 
> -- 
> Christopher R. Thorne, GIS Specialist
> -
> christhorne at sympatico.ca
> Tel:(613)523-6593, Ottawa ON Canada
> -----------------------------
>