/**
* Download srtm files for a specific latitude and longitude.
* @param int $lat
* @param int $lng
*/
function download_srtm_for($lat, $lon)
{
global $config;
$base_url = 'http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/';
$srtm_directory = get_srtm_directory() . "/";
$fname = srtm::get_filename($lat, $lon);
$zip_fname = $fname . '.zip';
$regions = array('Africa', 'Australia', 'Eurasia', 'Islands', 'North_America', 'South_America');
/*
* Search file in all regions
*/
foreach ($regions as $region) {
if (!($srtm_data = @file_get_contents($base_url . '/' . $region . '/' . $zip_fname))) {
continue;
}
file_put_contents($srtm_directory . $zip_fname, $srtm_data);
if (!($zip = zip_open($srtm_directory . $zip_fname))) {
die("Cannot unzip file \"" . $srtm_directory . $zip_fname . "\"\n");
}
while ($e = zip_read($zip)) {
if (zip_entry_name($e) !== $fname) {
continue;
}
zip_entry_open($zip, $e, "r");
$uncompressed = zip_entry_read($e, zip_entry_filesize($e));
file_put_contents($srtm_directory . $fname, $uncompressed);
zip_close($zip);
unlink($srtm_directory . $zip_fname);
return true;
}
}
die("Cannot find tile for {$lat},{$lon}\" in any region.\n");
}
public static function get_filename($lat, $lon)
{
$ll = srtm::get_lat_long_adjustments($lat, $lon);
//print_R($ll);
//always return filename with positive numbers (eg S-33 -> S33)
return $ll['lat_dir'] . sprintf("%02.0f", abs((int) ($lat + $ll['lat_adj']))) . $ll['lon_dir'] . sprintf("%03.0f", abs((int) ($lon + $ll['lon_adj']))) . '.hgt';
}
public static function get_filename($lat, $lon)
{
$ll = srtm::get_lat_long_adjustments($lat, $lon);
//print_R($ll);
$n_lat = $lat + $ll['lat_adj'];
$n_lon = $lon + $ll['lon_adj'];
return $ll['lat_dir'] . sprintf("%02.0f", abs((int) ($lat + $ll['lat_adj']))) . $ll['lon_dir'] . sprintf("%03.0f", abs((int) ($lon + $ll['lon_adj']))) . '.hgt';
}
function get_elevation($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;
/*
Exracting data from NASA .hgt files?
Here is a description from www2.jpl.nasa.gov/srtm/faq.html:
* The SRTM data files have names like "N34W119.hgt". What do the letters and numbers refer to, and what is ".hgt" format?
*
* Each data file covers a one-degree-of-latitude by one-degree-of-longitude block of Earth's surface.
* The first seven characters indicate the southwest corner of the block, with N, S, E, and W referring
* to north, south, east, and west. Thus, the "N34W119.hgt" file covers
* latitudes 34 to 35 North and
* longitudes 118-119 West
* (this file includes downtown Los Angeles, California).
* The filename extension ".hgt" simply stands for the word "height", meaning elevation.
* It is NOT a format type. These files are in "raw" format (no headers and not compressed),
* 16-bit signed integers, elevation measured in meters above sea level, in a
* "geographic" (latitude and longitude array) projection, with data voids indicated by -32768.
*
* International 3-arc-second files have 1201 columns and 1201 rows of data, with a total filesize
* of 2,884,802 bytes ( = 1201 x 1201 x 2).
*
* United States 1-arc-second files have 3601 columns and 3601 rows of data, with a total filesize
* of 25,934,402 bytes ( = 3601 x 3601 x 2).
*
* For more information read the text file "SRTM_Topo.txt" at http://dds.cr.usgs.gov/srtm/version1/Documentation/SRTM_Topo.txt
*** S-WiND ***
Due to the nature of HGT files, we must read the HGT differently depending if the location is
North or South of the equator.
- We read them as 2 byte binary
- check against http://www.heywhatsthat.com/profiler.html
A HGT file records elevations within a square.
Data is stored from the upper left corner. --> +----+
| |
| |
The File is named from its lower left corner --> +----+
*** Not implimented until required ***
USA has 1-arc-second files (its like HD for HGT files)
* These require 3601 rows + colums,
* so if it is ever needed, the calcs below need adjusting and testing for that.
jammin - 31/1/2016
*/
if ($lat_dir == "S") {
//South of the equator offset
//Round ensures a whole number for pixel
$line = (int) (((int) $lat - $lat) * 1201) * 1201;
$pixel = round(($lon - (int) $lon) * 1201);
$offset = ($line + $pixel) * 2;
} else {
//North of the equator offset
/* (un-modified WiND version)
$offset = ( (integer)(($x - (integer)$x + $lon_adj) * 1200)
* 2 + (1200 - (integer)(($y - (integer)$y + $lat_adj) * 1200))
* 2402 );
*/
$line = 1200 - (int) (($y - (int) $y + $lat_adj) * 1200);
$pixel = (int) (($x - (int) $x + $lon_adj) * 1200) * 2;
$offset = $pixel + $line * 2402;
}
//Debug
if (isset($main->userdata->privileges['admin']) && $main->userdata->privileges['admin'] === TRUE && $vars['debug']['enabled'] == TRUE) {
echo "DEBUG - SRTM.php - filename:{$filename},\n lat:{$lat}, lat_dir:{$lat_dir}\n lon:{$lon}, lon_dir:{$lon_dir}\n Line:{$line}, pixel:{$pixel}, offset:{$offset}<br />\n";
}
fseek($file, $offset);
//reverse string - file read (handle, length)
$h1 = $h2 = srtm::bytes2int(strrev(fread($file, 2)));
fseek($file, $offset - 2402);
$h3 = $h4 = srtm::bytes2int(strrev(fread($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 (smooths landscape from jutting out)
$elevation = ($h1 * (1 - $fx) + $h2 * $fx) * (1 - $fy) + ($h3 * (1 - $fx) + $h4 * $fx) * $fy;
if ($round) {
$elevation = round($elevation);
}
return $elevation;
}
<?php
require_once dirname(__FILE__) . '/../../globals/classes/srtm.php';
// Calculate needed files
$needed_files = array();
$bounds = $_SESSION['config']['map']['bounds'];
for ($lat = floor($bounds['min_latitude']); $lat <= ceil($bounds['max_latitude']); $lat += 1) {
// Clamp
if ($lat > 90) {
$lat = -90;
}
for ($lng = floor($bounds['min_longitude']); $lng <= ceil($bounds['max_longitude']); $lng += 1) {
// clamp
if ($lng > 180) {
$lng = -180;
}
$fname = srtm::get_filename($lat, $lng);
$needed_files[$fname] = array('exists' => file_exists(dirname(__FILE__) . '/../../files/srtm/' . $fname), 'lat' => $lat, 'lng' => $lng);
}
}
$web_folders = array('Africa', 'Australia', 'Eurasia', 'Islands', 'North_America', 'South_America');
if (!extension_loaded('zip') || !function_exists('zip_open')) {
show_error('You need <strong>"zip"</strong> extension to download srtm files.');
return true;
}
echo '<ul class="srtm">';
foreach ($needed_files as $fname => $data) {
echo '<li data-lat="' . $data['lat'] . '" data-lng="' . $data['lng'] . '" class="' . ($data['exists'] ? 'existing' : 'missing') . '">' . '<span>' . $fname . '</span></li>';
}
echo '</ul>';
echo '<div style="clear: both;"> </div>';
?>
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
ini_set('max_execution_time', 300);
header('Content-Type: application/json');
require_once dirname(__FILE__) . '/../globals/classes/srtm.php';
if (!isset($_GET['lat']) || !isset($_GET['lng'])) {
return;
}
$base_url = 'http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/';
$srtm_directory = dirname(__FILE__) . '/../files/srtm/';
$fname = srtm::get_filename((int) $_GET['lat'], (int) $_GET['lng']);
$zip_fname = $fname . '.zip';
$regions = array('Africa', 'Australia', 'Eurasia', 'Islands', 'North_America', 'South_America');
/*
* Search file in all regions
*/
foreach ($regions as $region) {
if (!($srtm_data = @file_get_contents($base_url . '/' . $region . '/' . $zip_fname))) {
continue;
}
file_put_contents($srtm_directory . $zip_fname, $srtm_data);
if (!($zip = zip_open($srtm_directory . $zip_fname))) {
echo json_encode(array('result' => '500', 'error' => 'cannot unzip'));
return;
}
while ($e = zip_read($zip)) {