function get_elevation($lat, $lon, $round = TRUE)
{
$y = $lat;
$x = $lon;
$filename = $this->data_path . 'N' . (int) $lat . 'E' . ((int) $lon < 100 ? '0' . (int) $lon : (int) $lon) . '.hgt';
if ($lat == '' || $lon == '' || !file_exists($filename)) {
return FALSE;
}
$file = fopen($filename, 'r');
$offset = (int) (($x - (int) $x) * 1200) * 2 + (1200 - (int) (($y - (int) $y) * 1200)) * 2402;
fseek($file, $offset);
$h1 = bytes2int(strrev(fread($file, 2)));
$h2 = bytes2int(strrev(fread($file, 2)));
fseek($file, $offset - 2402);
$h3 = bytes2int(strrev(fread($file, 2)));
$h4 = bytes2int(strrev(fread($file, 2)));
fclose($file);
$m = max($h1, $h2, $h3, $h4);
for ($i = 1; $i <= 4; $i++) {
$c = 'h' . $i;
if (${$c} == -32768) {
${$c} = $m;
}
}
$fx = ($lon - (int) ($lon * 1200) / 1200) * 1200;
$fy = ($lat - (int) ($lat * 1200) / 1200) * 1200;
// normalizing data
$elevation = ($h1 * (1 - $fx) + $h2 * $fx) * (1 - $fy) + ($h3 * (1 - $fx) + $h4 * $fx) * $fy;
if ($round) {
$elevation = round($elevation);
}
return $elevation;
}
function get_elevation($lat, $lon, $round = TRUE)
{
$filename = $this->data_path . $this->get_filename($lat, $lon);
if ($lat === '' || $lon === '' || !file_exists($filename)) {
return FALSE;
}
$file = fopen($filename, 'r');
$ll = $this->get_lat_long_adjustments($lat, $lon);
$lat_dir = $ll['lat_dir'];
$lat_adj = $ll['lat_adj'];
$lon_dir = $ll['lon_dir'];
$lon_adj = $ll['lon_adj'];
$y = $lat;
$x = $lon;
$offset = (int) (($x - (int) $x + $lon_adj) * 1200) * 2 + (1200 - (int) (($y - (int) $y + $lat_adj) * 1200)) * 2402;
fseek($file, $offset);
$h1 = bytes2int(strrev(fread($file, 2)));
$h2 = bytes2int(strrev(fread($file, 2)));
fseek($file, $offset - 2402);
$h3 = bytes2int(strrev(fread($file, 2)));
$h4 = bytes2int(strrev(fread($file, 2)));
fclose($file);
$m = max($h1, $h2, $h3, $h4);
for ($i = 1; $i <= 4; $i++) {
$c = 'h' . $i;
if (${$c} == -32768) {
${$c} = $m;
}
}
$fx = ($lon - (int) ($lon * 1200) / 1200) * 1200;
$fy = ($lat - (int) ($lat * 1200) / 1200) * 1200;
// normalizing data
$elevation = ($h1 * (1 - $fx) + $h2 * $fx) * (1 - $fy) + ($h3 * (1 - $fx) + $h4 * $fx) * $fy;
if ($round) {
$elevation = round($elevation);
}
return $elevation;
}
function get_elevation($lat, $lon, $round = TRUE)
{
$filename = $this->data_path . $this->get_filename($lat, $lon);
if ($lat === '' || $lon === '' || !file_exists($filename)) {
return FALSE;
}
$file = fopen($filename, 'r');
$ll = $this->get_lat_long_adjustments($lat, $lon);
$lat_dir = $ll['lat_dir'];
$lat_adj = $ll['lat_adj'];
$lon_dir = $ll['lon_dir'];
$lon_adj = $ll['lon_adj'];
$y = $lat;
$x = $lon;
//whole number - full number * lines (1201)
// * (
$line = (int) (((int) $lat - $lat) * 1201);
$pixel = round(($lon - (int) $lon) * 1201);
//Debug
if (isset($_SESSION['userdata']['id']) && $_SESSION['userdata']['id'] == "-1") {
//echo "filename:$filename, lat:$lat, lon:$lon\n";
//echo "Line:$line, pixel:$pixel, iLine:$iLine,
//offset $offset_no_adj <br />\n";
}
//file naming is from lower left corner.
//data is stored within the file from the upper left corner.
$offset = ($line * 1201 + $pixel) * 2;
fseek($file, $offset);
//reverse string - file read (handle, length)
$h1 = bytes2int(strrev(fread($file, 2)));
if ($h1 == -32768) {
$h1 = 0;
}
fclose($file);
return $h1;
}
