gnom.php
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<?php
/**
* Author : Julien Moquet
*
* Inspired by Proj4php from Mike Adair madairATdmsolutions.ca
* and Richard Greenwood rich@greenwoodma$p->com
* License: LGPL as per: http://www.gnu.org/copyleft/lesser.html
*/
/*****************************************************************************
NAME GNOMONIC
PURPOSE: Transforms input longitude and latitude to Easting and
Northing for the Gnomonic Projection.
Implementation based on the existing sterea and ortho
implementations.
PROGRAMMER DATE
---------- ----
Richard Marsden November 2009
ALGORITHM REFERENCES
1. Snyder, John P., "Flattening the Earth - Two Thousand Years of Map
Projections", University of Chicago Press 1993
2. Wolfram Mathworld "Gnomonic Projection"
http://mathworld.wolfram.com/GnomonicProjection.html
Accessed: 12th November 2009
******************************************************************************/
class Proj4phpProjGnom {
/**
* Initialize the Gnomonic projection
*
* @todo $def not used in context...?
* @param type $def
*/
public function init( $def ) {
/* Place parameters in static storage for common use
------------------------------------------------- */
$this->sin_p14 = sin( $this->lat0 );
$this->cos_p14 = cos( $this->lat0 );
// Approximation for projecting points to the horizon (infinity)
$this->infinity_dist = 1000 * $this->a;
$this->rc = 1;
}
/* Gnomonic forward equations--mapping lat,long to x,y
--------------------------------------------------- */
public function forward( $p ) {
/*
$sinphi;
$cosphi; // sin and cos value
$dlon; // delta longitude value
$coslon; // cos of longitude
$ksp; // scale factor
$g;
*/
$lon = $p->x;
$lat = $p->y;
/* Forward equations
----------------- */
$dlon = Proj4php::$common->adjust_lon( $lon - $this->long0 );
$sinphi = sin( $lat );
$cosphi = cos( $lat );
$coslon = cos( $dlon );
$g = $this->sin_p14 * $sinphi + $this->cos_p14 * $cosphi * $coslon;
$ksp = 1.0;
if( (g > 0) || (abs( g ) <= Proj4php::$common->EPSLN) ) {
$x = $this->x0 + $this->a * $ksp * $cosphi * sin( $dlon ) / $g;
$y = $this->y0 + $this->a * $ksp * ($this->cos_p14 * $sinphi - $this->sin_p14 * $cosphi * $coslon) / $g;
} else {
Proj4php::reportError( "orthoFwdPointError" );
// Point is in the opposing hemisphere and is unprojectable
// We still need to return a reasonable point, so we project
// to infinity, on a bearing
// equivalent to the northern hemisphere equivalent
// This is a reasonable approximation for short shapes and lines that
// straddle the horizon.
$x = $this->x0 + $this->infinity_dist * $cosphi * sin( $dlon );
$y = $this->y0 + $this->infinity_dist * ($this->cos_p14 * $sinphi - $this->sin_p14 * $cosphi * $coslon);
}
$p->x = $x;
$p->y = $y;
return $p;
}
/**
*
* @param type $p
* @return type
*/
public function inverse( $p ) {
/*
$rh; // Rho
$z; // angle
$sinc;
$cosc;
$c;
$lon;
$lat;
*/
/* Inverse equations
----------------- */
$p->x = ($p->x - $this->x0) / $this->a;
$p->y = ($p->y - $this->y0) / $this->a;
$p->x /= $this->k0;
$p->y /= $this->k0;
if( ($rh = sqrt( $p->x * $p->x + $p->y * $p->y ) ) ) {
$c = atan2( $rh, $this->rc );
$sinc = sin( $c );
$cosc = cos( $c );
$lat = Proj4php::$common->asinz( $cosc * $this->sin_p14 + ($p->y * $sinc * $this->cos_p14) / $rh );
$lon = atan2( $p->x * sinc, rh * $this->cos_p14 * $cosc - $p->y * $this->sin_p14 * $sinc );
$lon = Proj4php::$common->adjust_lon( $this->long0 + $lon );
} else {
$lat = $this->phic0;
$lon = 0.0;
}
$p->x = $lon;
$p->y = $lat;
return $p;
}
}
Proj4php::$proj['gnom'] = new Proj4phpProjGnom();