[mapguide-users] Transform coordinates from a BC, Canada Albers projection to geographic

[Bruce A]

Frank,

Thanks for the response. I get the following message vs. valid results…:
	>“ERROR: The coordinate system transform failed. PROJ4 failed to transform 
                > the data.
I am using MapGuide Open Source V. 1.1 (MgServerSetup-1.1.0.exe)

Do I need to set something different up for this projection on the server?

The email contains the contents of my php test file (alb2geo.php) - Did you
try creating and running this php file?
Could you provide me with the details of your testespg function? Perhaps I
could identify the issue based on your code…

I agree with your naming convention however the db file that I am using is
structured the reverse and thus the variable names…

Thanks again for your assistance. It is greatly appreciated.

Bruce


Frank Warmerdam-2 wrote:
> 
> Bruce A wrote:
>> I am trying to transform coordinates from a BC, Canada Albers projection
>> to
>> geographic and I cannot get the correct results using Mapguide’s WKT and
>> transformation capabilities.
>> 
>> The PHP code below outlines the WKT for the reference systems above (I
>> believe) and the transformation code. I have tried several permutations
>> of
>> the WKT for the projection without success. I am not certain that the
>> definition being used is correct… However, if I use what I believe to be
>> the
>> “correct” definition – the transformation produces an error outlined
>> below
>> and others although they do not produce an error produce incorrect
>> results.
>> 
>> “ERROR: The coordinate system transform failed. PROJ4 failed to transform
>> the data.
> ...
>> 	 	$wktGeo = 'GEOGCS["Longitude/Latitude(NAD 83)",DATUM["NAD 83",
>> SPHEROID
>> ["GRS 80", 6378137, 298.257222101]], RRIMEM [ "Greenwich", 0.000000 ],
>> UNIT
>> ["Decimal Degree", 0.01745329251994330]]';		
>> 		 
>> 		$wktAlb = 'PROJCS["BC_Albers",
>> GEOGCS["LL83",DATUM["NAD83",SPHEROID["GRS1980",6378137.000,298.257222101]],PRIMEM["Greenwich",
>> 0],UNIT["Degree",0.01745329251994330]],PROJECTION["Albers_Conic_Equal_Area"],PARAMETER["false_easting",1000000.000],PARAMETER["false_northing",0.000],PARAMETER["standard_parallel_1",58.500000],PARAMETER["standard_parallel_2",50.0],PARAMETER["latitude_of_origin",45.0000],PARAMETER["central_meridian",-126.000000],UNIT["Meter",1.00000],AUTHORITY["EPSG","3005"]]';
> ...
>> 		//$xProj = $point.X;
>> 		//$yProj = $point.Y;
>> 		$xProj = 1094382;
>> 		$yProj = 448309;
>> 		
>> 		$xLat = 49.05958;
>> 		$yLon = -122.8836876;
> 
> Bruce,
> 
> I tried converting from your geographic to your BC Albers with your
> WKT definition and I got:
> 
> warmerda at amd64[132]% testepsg -t 1.wkt 2.wkt -122.8836876 49.05958
> (-122.883688,49.059580,0.000000) ->
> (1227954.325206,454269.784357,0.000000)
> 
> I notice you refer to xLat, and yLon, shouldn't that properly be the
> following?
> 
> $xLon = -122.8836876;
> $yLat =  49.05958;
> 
> The "testepsg" transformation I did is using GDAL/OGR and PROJ from the
> current development version while MapGuide uses a somewhat older version.
> But I don't know of any obvious recent changes in PROJ.4 or OGR with
> regard to handling of Albers Conic Equal Area.
> 
> What values are you getting?  How exactly do you expect to get the
> projected coordinates you quoted?  BTW, I also tried the following
> which should be equivelent using EPSG lookups for NAD83 and BC Albers
> and I get the same output, so I think your WKT is fine.
> 
> warmerda at amd64[134]% testepsg -t NAD83 EPSG:3005 -122.8836876 49.05958
> (-122.883688,49.059580,0.000000) ->
> (1227954.325206,454269.784357,0.000000)
> 
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
> 
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> mapguide-users at lists.osgeo.org
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> 
> 

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