http://itsvr.altervista.org/ Script in PHP for your website to plot a GPS position on a custom map converting latitude and longitude from degrees to pixels.

deg-to-px.php

<?php

    // Demo: http://itsvr.altervista.org/

    /* Square area edges in degrees of your custom area map (Verona, Italy) */
    $mapLatTop      = 45.47;
    $mapLatBottom   = 45.37;
    $mapLonLeft     = 10.92;
    $mapLonRight    = 11.06;

    $mapLatDelta = $mapLatTop - $mapLatBottom;
    $mapLonDelta = $mapLonRight - $mapLonLeft;

    $worldMapWidth = 180/($mapLonDelta*M_PI);
    $f = sin($mapLatBottom*(M_PI/180));
    $mapOffsetY = $worldMapWidth/2*log((1+$f)/(1-$f));
    $f = sin($mapLatTop*(M_PI/180));
    $mapOffsetTopY = $worldMapWidth/2*log((1+$f)/(1-$f));
    $mapHeightNew = $mapOffsetTopY-$mapOffsetY;
    $mapRatioHeight = 1/$mapHeightNew;
    $mapRatioWidth = 1/$mapHeightNew;

    /**
     * deg_to_px($lat, $lon)
     *
     * Convert a GPS position on your custom map converting latitude and longitude from degrees to pixels
     *
     * @param (decimal(10,8)) $lat Latitude
     * @param (decimal(10,8)) $lon Longitude
     * @return (array()) array($x,$y) X and Y position in pixels
     */
    function deg_to_px($lat, $lon) {
        global $mapLonLeft, $mapLonDelta, $mapRatioWidth, $mapHeightNew, $worldMapWidth, $mapOffsetY;

        $x = ($lon-$mapLonLeft)*($mapRatioWidth/$mapLonDelta);

        $f = sin($lat*M_PI/180);
        $y = ($mapHeightNew-(($worldMapWidth/2*log((1+$f)/(1-$f)))-$mapOffsetY));

        return array($x,$y);
    }

?>