[MetaCRS] Problem with NAD27

[Mike Adair]

Micho,

Proj4js currently only supports the 3 and 7 parameter datum 
transformations (i.e. using the towgs84 parameter) and as such the NAD27 
Datum definition should probably be removed from Proj4js.  The issue is 
that the grid files specified by the @ parameters are very large and 
would be difficult to handle on the client side in a reasonable way.

Mike

Micho Gar wrote:
> Hi all,
>
> I am working with proj4js and I have encoutered this problem. In the 
> function deriveConstants, do this:
>
>       if (this.nagrids == '@null') this.datumCode = 'none';
>       if (this.datumCode && this.datumCode != 'none') {
>         var datumDef = Proj4js.Datum[this.datumCode];
>         if (datumDef) {
>           this.datum_params = datumDef.towgs84.split(',');
>           this.ellps = datumDef.ellipse;
>           this.datumName = datumDef.datumName ? datumDef.datumName : 
> this.datumCode;
>         }
>       }
>
> but the NAD27 datum definitions is:
>
> "NAD27": {nadgrids: "@conus, at alaska, at ntv2_0.gsb, at ntv1_can.dat", 
> ellipse: "clrk66", datumName: "North_American_Datum_1927"},
>
> he do not have the towgs84 term like the NAD83 for example:
>
> "NAD83": {towgs84: "0,0,0", ellipse: "GRS80", datumName: 
> "North_American_Datum_1983"},
>
> and when the function attemp to calculate the datum_params, he gives 
> the error:
>
> Error: datumDef.towgs84 is undefined
> Archivo de origen: 
> http://op915190.mma.es/WmsViewer/javascript/lib/proj4js/lib/proj4js.js
> Línea: 680
>
> Thanks to all.
>
>
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-- 
   Michael Adair
   Senior Software Architect
   DM Solutions Group Inc.

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