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<?php
/*------------------------------------------------------------------------------
** File:                gPoint.php
** Description: PHP class to convert Latitude & Longitude coordinates into
**                              UTM & Lambert Conic Conformal Northing/Easting coordinates. 
** Version:             1.3
** Author:              Brenor Brophy
** Email:               brenor dot brophy at gmail dot com
** Homepage:    brenorbrophy.com 
**------------------------------------------------------------------------------
** COPYRIGHT (c) 2005, 2006, 2007, 2008 BRENOR BROPHY
**
** The source code included in this package is free software; you can
** redistribute it and/or modify it under the terms of the GNU General Public
** License as published by the Free Software Foundation. This license can be
** read at:
**
** http://www.opensource.org/licenses/gpl-license.php
**
** This program is distributed in the hope that it will be useful, but WITHOUT 
** ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS 
** FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. 
**------------------------------------------------------------------------------
**
** Code for datum and UTM conversion was converted from C++ code written by
** Chuck Gantz (chuck dot gantz at globalstar dot com) from
** http://www.gpsy.com/gpsinfo/geotoutm/ This URL has many other references to
** useful information concerning conversion of coordinates.
**
** Rev History
** -----------------------------------------------------------------------------
** 1.0  08/25/2005      Initial Release
** 1.1  05/15/2006      Added software license language to header comments
**                                      Fixed an error in the convertTMtoLL() method. The latitude
**                                      calculation had a bunch of variables without $ symbols.
**                                      Fixed an error in convertLLtoTM() method, The $this-> was
**                                      missing in front of a couple of variables. Thanks to Bob
**                                      Robins of Maryland for catching the bugs.
** 1.2  05/18/2007      Added default of NULL to $LongOrigin arguement in convertTMtoLL()
**                                      and convertLLtoTM() to eliminate warning messages when the
**                                      methods are called without a value for $LongOrigin.
** 1.3  02/21/2008      Fixed a bug in the distanceFrom method, where the input parameters
**                                      were not being converted to radians prior to calculating the
**                                      distance. Thanks to Enrico Benco for finding pointing it out.
*/
define ("meter2nm", (1/1852));
define ("nm2meter", 1852);

/*------------------------------------------------------------------------------
** class gPoint         ... for Geographic Point
**
** This class encapsulates the methods for representing a geographic point on the
** earth in three different coordinate systema. Lat/Long, UTM and Lambert Conic
** Conformal.
*/
class gPoint
{
/* Reference ellipsoids derived from Peter H. Dana's website- 
** http://www.colorado.edu/geography/gcraft/notes/datum/datum_f.html
** email: pdana@pdana.com, web page: www.pdana.com
**
** Source:
** Defense Mapping Agency. 1987b. DMA Technical Report: Supplement to Department
** of Defense World Geodetic System 1984 Technical Report. Part I and II.
** Washington, DC: Defense Mapping Agency
*/
        var $ellipsoid = array(//Ellipsoid name, Equatorial Radius, square of eccentricity      
        "Airy"                                  =>array (6377563, 0.00667054),
        "Australian National"   =>array (6378160, 0.006694542),
        "Bessel 1841"                   =>array (6377397, 0.006674372),
        "Bessel 1841 Nambia"    =>array (6377484, 0.006674372),
        "Clarke 1866"                   =>array (6378206, 0.006768658),
        "Clarke 1880"                   =>array (6378249, 0.006803511),
        "Everest"                               =>array (6377276, 0.006637847),
        "Fischer 1960 Mercury"  =>array (6378166, 0.006693422),
        "Fischer 1968"                  =>array (6378150, 0.006693422),
        "GRS 1967"                              =>array (6378160, 0.006694605),
        "GRS 1980"                              =>array (6378137, 0.00669438),
        "Helmert 1906"                  =>array (6378200, 0.006693422),
        "Hough"                                 =>array (6378270, 0.00672267),
        "International"                 =>array (6378388, 0.00672267),
        "Krassovsky"                    =>array (6378245, 0.006693422),
        "Modified Airy"                 =>array (6377340, 0.00667054),
        "Modified Everest"              =>array (6377304, 0.006637847),
        "Modified Fischer 1960" =>array (6378155, 0.006693422),
        "South American 1969"   =>array (6378160, 0.006694542),
        "WGS 60"                                =>array (6378165, 0.006693422),
        "WGS 66"                                =>array (6378145, 0.006694542),
        "WGS 72"                                =>array (6378135, 0.006694318),
        "WGS 84"                                =>array (6378137, 0.00669438));

        // Properties
        var $a;                                                                         // Equatorial Radius
        var     $e2;                                                                    // Square of eccentricity
        var     $datum;                                                                 // Selected datum
        var     $Xp, $Yp;                                                               // X,Y pixel location
        var $lat, $long;                                                        // Latitude & Longitude of the point
        var $utmNorthing, $utmEasting, $utmZone;        // UTM Coordinates of the point
        var     $lccNorthing, $lccEasting;                              // Lambert coordinates of the point
        var $falseNorthing, $falseEasting;                      // Origin coordinates for Lambert Projection
        var $latOfOrigin;                                                       // For Lambert Projection
        var $longOfOrigin;                                                      // For Lambert Projection
        var $firstStdParallel;                                          // For lambert Projection
        var $secondStdParallel;                                         // For lambert Projection

        // constructor
        function gPoint($datum='WGS 84')                        // Default datum is WGS 84
        {
                $this->a = $this->ellipsoid[$datum][0];         // Set datum Equatorial Radius
                $this->e2 = $this->ellipsoid[$datum][1];        // Set datum Square of eccentricity
                $this->datum = $datum;                                          // Save the datum
        }
        //
        // Set/Get X & Y pixel of the point (used if it is being drawn on an image)
        //
        function setXY($x, $y)
        {
                $this->Xp = $x; $this->Yp = $y;
        }
        function Xp() { return $this->Xp; }
        function Yp() { return $this->Yp; }
        //
        // Set/Get/Output Longitude & Latitude of the point
        //
        function setLongLat($long, $lat)
        {
                $this->long = $long; $this->lat = $lat;
        }
        function Lat() { return $this->lat; }
        function Long() { return $this->long; }
        function printLatLong() { printf("Latitude: %1.5f Longitude: %1.5f",$this->lat, $this->long); }
        //
        // Set/Get/Output Universal Transverse Mercator Coordinates
        //
        function setUTM($easting, $northing, $zone='')  // Zone is optional
        {
                $this->utmNorthing = $northing;
                $this->utmEasting = $easting;
                $this->utmZone = $zone;
        }
        function N() { return $this->utmNorthing; }
        function E() { return $this->utmEasting; }
        function Z() { return $this->utmZone; }
        function printUTM() { print( "Northing: ".(int)$this->utmNorthing.", Easting: ".(int)$this->utmEasting.", Zone: ".$this->utmZone); }
        //
        // Set/Get/Output Lambert Conic Conformal Coordinates
        //
        function setLambert($easting, $northing)
        {
                $this->lccNorthing = $northing;
                $this->lccEasting = $easting;
        }
        function lccN() { return $this->lccNorthing; }
        function lccE() { return $this->lccEasting; }
        function printLambert() { print( "Northing: ".(int)$this->lccNorthing.", Easting: ".(int)$this->lccEasting); }

//------------------------------------------------------------------------------
//
// Convert Longitude/Latitude to UTM
//
// Equations from USGS Bulletin 1532 
// East Longitudes are positive, West longitudes are negative. 
// North latitudes are positive, South latitudes are negative
// Lat and Long are in decimal degrees
// Written by Chuck Gantz- chuck dot gantz at globalstar dot com, converted to PHP by
// Brenor Brophy, brenor dot brophy at gmail dot com
//
// UTM coordinates are useful when dealing with paper maps. Basically the
// map will can cover a single UTM zone which is 6 degrees on longitude.
// So you really don't care about an object crossing two zones. You just get a
// second map of the other zone. However, if you happen to live in a place that
// straddles two zones (For example the Santa Babara area in CA straddles zone 10
// and zone 11) Then it can become a real pain having to have two maps all the time.
// So relatively small parts of the world (like say California) create their own
// version of UTM coordinates that are adjusted to conver the whole area of interest
// on a single map. These are called state grids. The projection system is the
// usually same as UTM (i.e. Transverse Mercator), but the central meridian
// aka Longitude of Origin is selected to suit the logitude of the area being
// mapped (like being moved to the central meridian of the area) and the grid
// may cover more than the 6 degrees of lingitude found on a UTM map. Areas
// that are wide rather than long - think Montana as an example. May still
// have to have a couple of maps to cover the whole state because TM projection
// looses accuracy as you move further away from the Longitude of Origin, 15 degrees
// is usually the limit.
//
// Now, in the case where we want to generate electronic maps that may be
// placed pretty much anywhere on the globe we really don't to deal with the
// issue of UTM zones in our coordinate system. We would really just like a
// grid that is fully contigious over the area of the map we are drawing. Similiar
// to the state grid, but local to the area we are interested in. I call this
// Local Transverse Mercator and I have modified the function below to also
// make this conversion. If you pass a Longitude value to the function as $LongOrigin
// then that is the Longitude of Origin that will be used for the projection.
// Easting coordinates will be returned (in meters) relative to that line of
// longitude - So an Easting coordinate for a point located East of the longitude
// of origin will be a positive value in meters, an Easting coordinate for a point
// West of the longitude of Origin will have a negative value in meters. Northings
// will always be returned in meters from the equator same as the UTM system. The
// UTMZone value will be valid for Long/Lat given - thought it is not meaningful
// in the context of Local TM. If a NULL value is passed for $LongOrigin
// then the standard UTM coordinates are calculated.
//
        function convertLLtoTM($LongOrigin = NULL)
        {
                $k0 = 0.9996;
                $falseEasting = 0.0;

                //Make sure the longitude is between -180.00 .. 179.9
                $LongTemp = ($this->long+180)-(integer)(($this->long+180)/360)*360-180; // -180.00 .. 179.9;
                $LatRad = deg2rad($this->lat);
                $LongRad = deg2rad($LongTemp);

                if (!$LongOrigin)
                { // Do a standard UTM conversion - so findout what zone the point is in
                        $ZoneNumber = (integer)(($LongTemp + 180)/6) + 1;
                        // Special zone for South Norway
                        if( $this->lat >= 56.0 && $this->lat < 64.0 && $LongTemp >= 3.0 && $LongTemp < 12.0 ) // Fixed 1.1
                                $ZoneNumber = 32;
                        // Special zones for Svalbard
                        if( $this->lat >= 72.0 && $this->lat < 84.0 ) 
                        {
                                if(      $LongTemp >= 0.0  && $LongTemp <  9.0 ) $ZoneNumber = 31;
                                else if( $LongTemp >= 9.0  && $LongTemp < 21.0 ) $ZoneNumber = 33;
                                else if( $LongTemp >= 21.0 && $LongTemp < 33.0 ) $ZoneNumber = 35;
                                else if( $LongTemp >= 33.0 && $LongTemp < 42.0 ) $ZoneNumber = 37;
                        }
                        $LongOrigin = ($ZoneNumber - 1)*6 - 180 + 3;  //+3 puts origin in middle of zone
                        //compute the UTM Zone from the latitude and longitude
                        $this->utmZone = sprintf("%d%s", $ZoneNumber, $this->UTMLetterDesignator());
                        // We also need to set the false Easting value adjust the UTM easting coordinate
                        $falseEasting = 500000.0;
                }
                $LongOriginRad = deg2rad($LongOrigin);

                $eccPrimeSquared = ($this->e2)/(1-$this->e2);

                $N = $this->a/sqrt(1-$this->e2*sin($LatRad)*sin($LatRad));
                $T = tan($LatRad)*tan($LatRad);
                $C = $eccPrimeSquared*cos($LatRad)*cos($LatRad);
                $A = cos($LatRad)*($LongRad-$LongOriginRad);

                $M = $this->a*((1       - $this->e2/4           - 3*$this->e2*$this->e2/64      - 5*$this->e2*$this->e2*$this->e2/256)*$LatRad 
                                                        - (3*$this->e2/8        + 3*$this->e2*$this->e2/32      + 45*$this->e2*$this->e2*$this->e2/1024)*sin(2*$LatRad)
                                                                                                + (15*$this->e2*$this->e2/256 + 45*$this->e2*$this->e2*$this->e2/1024)*sin(4*$LatRad) 
                                                                                                - (35*$this->e2*$this->e2*$this->e2/3072)*sin(6*$LatRad));
        
                $this->utmEasting = ($k0*$N*($A+(1-$T+$C)*$A*$A*$A/6
                                                + (5-18*$T+$T*$T+72*$C-58*$eccPrimeSquared)*$A*$A*$A*$A*$A/120)
                                                + $falseEasting);

                $this->utmNorthing = ($k0*($M+$N*tan($LatRad)*($A*$A/2+(5-$T+9*$C+4*$C*$C)*$A*$A*$A*$A/24
                                         + (61-58*$T+$T*$T+600*$C-330*$eccPrimeSquared)*$A*$A*$A*$A*$A*$A/720)));
                if($this->lat < 0)
                        $this->utmNorthing += 10000000.0; //10000000 meter offset for southern hemisphere
        }
//
// This routine determines the correct UTM letter designator for the given latitude
// returns 'Z' if latitude is outside the UTM limits of 84N to 80S
// Written by Chuck Gantz- chuck dot gantz at globalstar dot com, converted to PHP by
// Brenor Brophy, brenor dot brophy at gmail dot com
//
        function UTMLetterDesignator()
        {       
                if((84 >= $this->lat) && ($this->lat >= 72)) $LetterDesignator = 'X';
                else if((72 > $this->lat) && ($this->lat >= 64)) $LetterDesignator = 'W';
                else if((64 > $this->lat) && ($this->lat >= 56)) $LetterDesignator = 'V';
                else if((56 > $this->lat) && ($this->lat >= 48)) $LetterDesignator = 'U';
                else if((48 > $this->lat) && ($this->lat >= 40)) $LetterDesignator = 'T';
                else if((40 > $this->lat) && ($this->lat >= 32)) $LetterDesignator = 'S';
                else if((32 > $this->lat) && ($this->lat >= 24)) $LetterDesignator = 'R';
                else if((24 > $this->lat) && ($this->lat >= 16)) $LetterDesignator = 'Q';
                else if((16 > $this->lat) && ($this->lat >= 8)) $LetterDesignator = 'P';
                else if(( 8 > $this->lat) && ($this->lat >= 0)) $LetterDesignator = 'N';
                else if(( 0 > $this->lat) && ($this->lat >= -8)) $LetterDesignator = 'M';
                else if((-8 > $this->lat) && ($this->lat >= -16)) $LetterDesignator = 'L';
                else if((-16 > $this->lat) && ($this->lat >= -24)) $LetterDesignator = 'K';
                else if((-24 > $this->lat) && ($this->lat >= -32)) $LetterDesignator = 'J';
                else if((-32 > $this->lat) && ($this->lat >= -40)) $LetterDesignator = 'H';
                else if((-40 > $this->lat) && ($this->lat >= -48)) $LetterDesignator = 'G';
                else if((-48 > $this->lat) && ($this->lat >= -56)) $LetterDesignator = 'F';
                else if((-56 > $this->lat) && ($this->lat >= -64)) $LetterDesignator = 'E';
                else if((-64 > $this->lat) && ($this->lat >= -72)) $LetterDesignator = 'D';
                else if((-72 > $this->lat) && ($this->lat >= -80)) $LetterDesignator = 'C';
                else $LetterDesignator = 'Z'; //This is here as an error flag to show that the Latitude is outside the UTM limits

                return($LetterDesignator);
        }

//------------------------------------------------------------------------------
//
// Convert UTM to Longitude/Latitude
//
// Equations from USGS Bulletin 1532 
// East Longitudes are positive, West longitudes are negative. 
// North latitudes are positive, South latitudes are negative
// Lat and Long are in decimal degrees. 
// Written by Chuck Gantz- chuck dot gantz at globalstar dot com, converted to PHP by
// Brenor Brophy, brenor dot brophy at gmail dot com
//
// If a value is passed for $LongOrigin then the function assumes that
// a Local (to the Longitude of Origin passed in) Transverse Mercator
// coordinates is to be converted - not a UTM coordinate. This is the
// complementary function to the previous one. The function cannot
// tell if a set of Northing/Easting coordinates are in the North
// or South hemesphere - they just give distance from the equator not
// direction - so only northern hemesphere lat/long coordinates are returned.
// If you live south of the equator there is a note later in the code
// explaining how to have it just return southern hemesphere lat/longs.
//
        function convertTMtoLL($LongOrigin = NULL)
        {
                $k0 = 0.9996;
                $e1 = (1-sqrt(1-$this->e2))/(1+sqrt(1-$this->e2));
                $falseEasting = 0.0;
                $y = $this->utmNorthing;

                if (!$LongOrigin)
                { // It is a UTM coordinate we want to convert
                        sscanf($this->utmZone,"%d%s",$ZoneNumber,$ZoneLetter);
                        if($ZoneLetter >= 'N')
                                $NorthernHemisphere = 1;//point is in northern hemisphere
                        else
                        {
                                $NorthernHemisphere = 0;//point is in southern hemisphere
                                $y -= 10000000.0;//remove 10,000,000 meter offset used for southern hemisphere
                        }
                        $LongOrigin = ($ZoneNumber - 1)*6 - 180 + 3;  //+3 puts origin in middle of zone
                        $falseEasting = 500000.0;
                }

//              $y -= 10000000.0;       // Uncomment line to make LOCAL coordinates return southern hemesphere Lat/Long
                $x = $this->utmEasting - $falseEasting; //remove 500,000 meter offset for longitude

                $eccPrimeSquared = ($this->e2)/(1-$this->e2);

                $M = $y / $k0;
                $mu = $M/($this->a*(1-$this->e2/4-3*$this->e2*$this->e2/64-5*$this->e2*$this->e2*$this->e2/256));

                $phi1Rad = $mu  + (3*$e1/2-27*$e1*$e1*$e1/32)*sin(2*$mu) 
                                        + (21*$e1*$e1/16-55*$e1*$e1*$e1*$e1/32)*sin(4*$mu)
                                        +(151*$e1*$e1*$e1/96)*sin(6*$mu);
                $phi1 = rad2deg($phi1Rad);

                $N1 = $this->a/sqrt(1-$this->e2*sin($phi1Rad)*sin($phi1Rad));
                $T1 = tan($phi1Rad)*tan($phi1Rad);
                $C1 = $eccPrimeSquared*cos($phi1Rad)*cos($phi1Rad);
                $R1 = $this->a*(1-$this->e2)/pow(1-$this->e2*sin($phi1Rad)*sin($phi1Rad), 1.5);
                $D = $x/($N1*$k0);

                $tlat = $phi1Rad - ($N1*tan($phi1Rad)/$R1)*($D*$D/2-(5+3*$T1+10*$C1-4*$C1*$C1-9*$eccPrimeSquared)*$D*$D*$D*$D/24
                                                +(61+90*$T1+298*$C1+45*$T1*$T1-252*$eccPrimeSquared-3*$C1*$C1)*$D*$D*$D*$D*$D*$D/720); // fixed in 1.1
                $this->lat = rad2deg($tlat);

                $tlong = ($D-(1+2*$T1+$C1)*$D*$D*$D/6+(5-2*$C1+28*$T1-3*$C1*$C1+8*$eccPrimeSquared+24*$T1*$T1)
                                                *$D*$D*$D*$D*$D/120)/cos($phi1Rad);
                $this->long = $LongOrigin + rad2deg($tlong);
        }

//------------------------------------------------------------------------------
// Configure a Lambert Conic Conformal Projection
//
// falseEasting & falseNorthing are just an offset in meters added to the final
// coordinate calculated.
//
// longOfOrigin & LatOfOrigin are the "center" latitiude and longitude of the
// area being projected. All coordinates will be calculated in meters relative
// to this point on the earth.
//
// firstStdParallel & secondStdParallel are the two lines of longitude (that
// is they run east-west) that define where the "cone" intersects the earth.
// Simply put they should bracket the area being projected. 
//
// google is your friend to find out more
//
        function configLambertProjection ($falseEasting, $falseNorthing,
                                                                          $longOfOrigin, $latOfOrigin,
                                                                          $firstStdParallel, $secondStdParallel)
        {
                $this->falseEasting = $falseEasting;
                $this->falseNorthing = $falseNorthing;
                $this->longOfOrigin = $longOfOrigin;
                $this->latOfOrigin = $latOfOrigin;
                $this->firstStdParallel = $firstStdParallel;
                $this->secondStdParallel = $secondStdParallel;
        }

//------------------------------------------------------------------------------
//
// Convert Longitude/Latitude to Lambert Conic Easting/Northing
//
// This routine will convert a Latitude/Longitude coordinate to an Northing/
// Easting coordinate on a Lambert Conic Projection. The configLambertProjection()
// function should have been called prior to this one to setup the specific
// parameters for the projection. The Northing/Easting parameters calculated are
// in meters (because the datum used is in meters) and are relative to the
// falseNorthing/falseEasting coordinate. Which in turn is relative to the
// Lat/Long of origin The formula were obtained from URL:
// http://www.ihsenergy.com/epsg/guid7_2.html.
// Code was written by Brenor Brophy, brenor dot brophy at gmail dot com
//
        function convertLLtoLCC()
        {
                $e = sqrt($this->e2);

                $phi    = deg2rad($this->lat);                                          // Latitude to convert
                $phi1   = deg2rad($this->firstStdParallel);                     // Latitude of 1st std parallel
                $phi2   = deg2rad($this->secondStdParallel);            // Latitude of 2nd std parallel
                $lamda  = deg2rad($this->long);                                         // Lonitude to convert
                $phio   = deg2rad($this->latOfOrigin);                          // Latitude of  Origin
                $lamdao = deg2rad($this->longOfOrigin);                         // Longitude of  Origin

                $m1 = cos($phi1) / sqrt(( 1 - $this->e2*sin($phi1)*sin($phi1)));
                $m2 = cos($phi2) / sqrt(( 1 - $this->e2*sin($phi2)*sin($phi2)));
                $t1 = tan((pi()/4)-($phi1/2)) / pow(( ( 1 - $e*sin($phi1) ) / ( 1 + $e*sin($phi1) )),$e/2);
                $t2 = tan((pi()/4)-($phi2/2)) / pow(( ( 1 - $e*sin($phi2) ) / ( 1 + $e*sin($phi2) )),$e/2);
                $to = tan((pi()/4)-($phio/2)) / pow(( ( 1 - $e*sin($phio) ) / ( 1 + $e*sin($phio) )),$e/2);
                $t  = tan((pi()/4)-($phi /2)) / pow(( ( 1 - $e*sin($phi ) ) / ( 1 + $e*sin($phi ) )),$e/2);
                $n      = (log($m1)-log($m2)) / (log($t1)-log($t2));
                $F      = $m1/($n*pow($t1,$n));
                $rf     = $this->a*$F*pow($to,$n);
                $r      = $this->a*$F*pow($t,$n);
                $theta = $n*($lamda - $lamdao);

                $this->lccEasting = $this->falseEasting + $r*sin($theta);
                $this->lccNorthing = $this->falseNorthing + $rf - $r*cos($theta);
        }
//------------------------------------------------------------------------------
//
// Convert Easting/Northing on a Lambert Conic projection to Longitude/Latitude
//
// This routine will convert a Lambert Northing/Easting coordinate to an
// Latitude/Longitude coordinate.  The configLambertProjection() function should
// have been called prior to this one to setup the specific parameters for the
// projection. The Northing/Easting parameters are in meters (because the datum
// used is in meters) and are relative to the falseNorthing/falseEasting
// coordinate. Which in turn is relative to the Lat/Long of origin The formula
// were obtained from URL http://www.ihsenergy.com/epsg/guid7_2.html. Code
// was written by Brenor Brophy, brenor dot brophy at gmail dot com
//
        function convertLCCtoLL()
        {
                $e = sqrt($this->e2);

                $phi1   = deg2rad($this->firstStdParallel);                     // Latitude of 1st std parallel
                $phi2   = deg2rad($this->secondStdParallel);            // Latitude of 2nd std parallel
                $phio   = deg2rad($this->latOfOrigin);                          // Latitude of  Origin
                $lamdao = deg2rad($this->longOfOrigin);                         // Longitude of  Origin
                $E              = $this->lccEasting;
                $N              = $this->lccNorthing;
                $Ef             = $this->falseEasting;
                $Nf             = $this->falseNorthing;

                $m1 = cos($phi1) / sqrt(( 1 - $this->e2*sin($phi1)*sin($phi1)));
                $m2 = cos($phi2) / sqrt(( 1 - $this->e2*sin($phi2)*sin($phi2)));
                $t1 = tan((pi()/4)-($phi1/2)) / pow(( ( 1 - $e*sin($phi1) ) / ( 1 + $e*sin($phi1) )),$e/2);
                $t2 = tan((pi()/4)-($phi2/2)) / pow(( ( 1 - $e*sin($phi2) ) / ( 1 + $e*sin($phi2) )),$e/2);
                $to = tan((pi()/4)-($phio/2)) / pow(( ( 1 - $e*sin($phio) ) / ( 1 + $e*sin($phio) )),$e/2);
                $n      = (log($m1)-log($m2)) / (log($t1)-log($t2));
                $F      = $m1/($n*pow($t1,$n));
                $rf     = $this->a*$F*pow($to,$n);
                $r_     = sqrt( pow(($E-$Ef),2) + pow(($rf-($N-$Nf)),2) );
                $t_     = pow($r_/($this->a*$F),(1/$n));
                $theta_ = atan(($E-$Ef)/($rf-($N-$Nf)));

                $lamda  = $theta_/$n + $lamdao;
                $phi0   = (pi()/2) - 2*atan($t_);
                $phi1   = (pi()/2) - 2*atan($t_*pow(((1-$e*sin($phi0))/(1+$e*sin($phi0))),$e/2));
                $phi2   = (pi()/2) - 2*atan($t_*pow(((1-$e*sin($phi1))/(1+$e*sin($phi1))),$e/2));
                $phi    = (pi()/2) - 2*atan($t_*pow(((1-$e*sin($phi2))/(1+$e*sin($phi2))),$e/2));
                
                $this->lat      = rad2deg($phi);
                $this->long = rad2deg($lamda);
        }

//------------------------------------------------------------------------------
// This is a useful function that returns the Great Circle distance from the
// gPoint to another Long/Lat coordinate
//
// Result is returned as meters
//
        function distanceFrom($lon1, $lat1)
        { 
                $lon1 = deg2rad($lon1); $lat1 = deg2rad($lat1); // Added in 1.3
                $lon2 = deg2rad($this->Long()); $lat2 = deg2rad($this->Lat());
 
                $theta = $lon2 - $lon1;
                $dist = acos(sin($lat1) * sin($lat2) + cos($lat1) * cos($lat2) * cos($theta));

//              Alternative formula supposed to be more accurate for short distances
//              $dist = 2*asin(sqrt( pow(sin(($lat1-$lat2)/2),2) + cos($lat1)*cos($lat2)*pow(sin(($lon1-$lon2)/2),2)));
                return ( $dist * 6366710 ); // from http://williams.best.vwh.net/avform.htm#GCF
        }

//------------------------------------------------------------------------------
// This function also calculates the distance between two points. In this case
// it just uses Pythagoras's theorm using TM coordinates.
//
        function distanceFromTM(&$pt)
        { 
                $E1 = $pt->E();         $N1 = $pt->N();
                $E2 = $this->E();       $N2 = $this->N();
 
                $dist = sqrt(pow(($E1-$E2),2)+pow(($N1-$N2),2));
                return $dist; 
        }

//------------------------------------------------------------------------------
// This function geo-references a geoPoint to a given map. This means that it
// calculates the x,y pixel coordinate that coresponds to the Lat/Long value of
// the geoPoint. The calculation is done using the Transverse Mercator(TM)
// coordinates of the gPoint with respect to the TM coordinates of the center
// point of the map. So this only makes sense if you are using Local TM
// projection.
//
// $rX & $rY are the pixel coordinates that corespond to the Northing/Easting
// ($rE/$rN) coordinate it is to this coordinate that the point will be
// geo-referenced. The $LongOrigin is needed to make sure the Easting/Northing
// coordinates of the point are correctly converted.
//
        function gRef($rX, $rY, $rE, $rN, $Scale, $LongOrigin)
        {
                $this->convertLLtoTM($LongOrigin);
                $x = (($this->E() - $rE) / $Scale)              // The easting in meters times the scale to get pixels
                                                                                                // is relative to the center of the image so adjust to
                        + ($rX);                                                        // the left coordinate.
                $y = $rY -                                                      // Adjust to bottom coordinate.
                        (($rN - $this->N()) / $Scale);          // The northing in meters
                                                                                                // relative to the equator. Subtract center point northing
                                                                                                // to get relative to image center and convert meters to pixels
                $this->setXY((int)$x,(int)$y);                  // Save the geo-referenced result.
        }
} // end of class gPoint

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