[mapserver-users] Calculating pixel coordinates from latlong

[Ken Patterson]

Hello,

We hope to liven up our backgrounds using Mapserver output from either the perl interface or using shp2img.  At this time we are trying to figure out how to map a world coordinates (lat/long) to pixel coordinates (from Perl).  I can create a background image with Perl Mapserver and save it to a png file then to be loaded back in w/ GD::newFromPng().  What Information do I need in order to translate from World (lat/long) to a pixel coordinate?  Is this something that can be done w/in the Perl Mapserver interface?  Has anyone gone through this and can provide some direction?

>From searching through the Mapserver archives it seems that the "true" Extent needs to be found and that a projection needs to take place.  I've seen some references to a Perl interface to Proj.4 but could not retrieve the files.  

Any help of ideas would be greatly appreciated!

Thanks,
    Ken

$map_path = <Path>/my.map";
$amap = new mapObj( "$map_path );

# ---------------------------- Set the image w/h 
$amap->{width} = 200;
$amap->{height} = 100;

# ------------------------------ Create my extent (Arizona) 
$myExtent = new rectObj();
$myExtent->{maxx} = -111.35;
$myExtent->{minx} = -112.97;
$myExtent->{maxy} = 33.62;
$myExtent->{miny} = 33.19;
$amap->{extent} = $myExtent;

# ----------------------------- Draw the maps
$image = $amap->draw();                                 
                                                                            
# ----------------------------- Save the bitmap 
$image_url = $image->saveImage( "/tmp/test.png", $mapscript::MS_PNG, 1, 1, 95 );

# ----------------------------- Get the image file to a GD image
my $backGroundImage = GD::Image->newFromPng( "/tmp/test.png" );

# ---------------------------- Want try draw some stuff on the image
my ( $vx, $vy ) = TranslateToViewport( ... )
# Draw my stuff at/around pt ( $vx, $vy )

If I'm understanding it correctly Mapserver is using a projection and the extent is altered as well.  
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