[mapguide-users] Transform Coordinates from MgPoint

[Jim O'Leary]

This code does actually work when you convert from BC Albers to LL84,
but you then have to convert the return point's x and y from rads to 
degrees.

$x = $x / M_PI * 180.0;// M_PI is the PHP constant for pi
$y = $y / M_PI * 180.0;

It fails when you convert from LL84 to BC Albers.

However, you can use methods of the MgCoordinateSystem object 
to convert back and forth.

$coordSysFactory = new MgCoordinateSystemFactory();
$geometryFactory = new MgGeometryFactory();
$coord = $geometryFactory->CreateCoordinateXY((double) $x, (double) $y);
 // creates an MgCoordinateSystem object
$coordSys = $coordSysFactory->Create($BC_Albers); // $BC_Albers is the WKT
if($currentSRS == 'albers')
{      
    $newCoord = $coordSys->ConvertToLonLat($coord);
}
else
{
    $newCoord = $coordSys->ConvertFromLonLat($coord);
}
$point = $geometryFactory->CreatePoint($newCoord);
$x = $point->GetCoordinate()->GetX();
$y = $point->GetCoordinate()->GetY();

Jim O wrote:
> 
> I am able to transform coordinates on the fly from a FeatureReader,
> but not from an MgPoint. Both codes below produce an MgGeometry object, 
> and both codes produce a $transform object like this:
> 
> $coordSysFactory = new MgCoordinateSystemFactory();
> $source = $coordSysFactory->Create($map->GetMapSRS());
> $target = $coordSysFactory->Create($LL84WKT);// $LL84WKT is a the WKT
> string for LL84
> $transform =  new MgCoordinateSystemTransform($source, $target);
> 
> I've pasted the doxygen comments in the code below for clarity.
> The FeatureReader code that works goes:
> 
> $agfWriter = new MgAgfReaderWriter();
> while ($featureReader->ReadNext())
> {
>     // MgByteReader *  GetGeometry (CREFSTRING propertyName)=0
>     // Gets the Geometry for the specified property.
>     $byteReader = $featureReader->GetGeometry('GEOMETRY');
>     // MgGeometry *  Read (MgByteReader *agf)
>     // Translates an MgByteReader object into an MgGeometry object.
>     $geometry = $agfReaderWriter->Read($byteReader);
>     $geometry = $geometry->Transform($transform);
> 
> The MgPoint code that doesn't work goes:
> 
> // MgCoordinate *  CreateCoordinateXY (double x, double y)
> // Creates an MgCoordinate object with Dimension = XY
> $coord = $geometryFactory->CreateCoordinateXY((double) $_REQUEST['x'],
> (double) $_REQUEST['y']);
> // MgPoint *  CreatePoint (MgCoordinate *coordinate)
> // Creates a point from a coordinate.
> $point = $geometryFactory->CreatePoint($coord);
> // MgPoint is a subclass of MgGeometry
> $point = $point->Transform($transform);
> 
> One MgGeometry object can transform, but one cannot. All I get from the
> second is a nonsense number. Suggestions?
> 

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