PHP PostGIS to GeoJSON

postgis_geojson.php

<?php
/**
 * PostGIS to GeoJSON
 * Query a PostGIS table or view and return the results in GeoJSON format, suitable for use in OpenLayers, Leaflet, etc.
 * 
 * @param 		string		$geotable		The PostGIS layer name *REQUIRED*
 * @param 		string		$geomfield		The PostGIS geometry field *REQUIRED*
 * @param 		string		$srid			The SRID of the returned GeoJSON *OPTIONAL (If omitted, EPSG: 4326 will be used)*
 * @param 		string 		$fields 		Fields to be returned *OPTIONAL (If omitted, all fields will be returned)* NOTE- Uppercase field names should be wrapped in double quotes
 * @param 		string		$parameters		SQL WHERE clause parameters *OPTIONAL*
 * @param 		string		$orderby		SQL ORDER BY constraint *OPTIONAL*
 * @param 		string		$sort			SQL ORDER BY sort order (ASC or DESC) *OPTIONAL*
 * @param 		string		$limit			Limit number of results returned *OPTIONAL*
 * @param 		string		$offset			Offset used in conjunction with limit *OPTIONAL*
 * @return 		string					resulting geojson string
 */
function escapeJsonString($value) { # list from www.json.org: (\b backspace, \f formfeed)
  $escapers = array("\\", "/", "\"", "\n", "\r", "\t", "\x08", "\x0c");
  $replacements = array("\\\\", "\\/", "\\\"", "\\n", "\\r", "\\t", "\\f", "\\b");
  $result = str_replace($escapers, $replacements, $value);
  return $result;
}
 
# Retrive URL variables
if (empty($_GET['geotable'])) {
    echo "missing required parameter: <i>geotable</i>";
    exit;
} else
    $geotable = $_GET['geotable'];

if (empty($_GET['geomfield'])) {
    echo "missing required parameter: <i>geomfield</i>";
    exit;
} else
    $geomfield = $_GET['geomfield'];

if (empty($_GET['srid'])) {
    $srid = '4326';
} else
    $srid = $_GET['srid'];

if (empty($_GET['fields'])) {
    $fields = '*';
} else
    $fields = $_GET['fields'];

$parameters = $_GET['parameters'];

$orderby    = $_GET['orderby'];

if (empty($_GET['sort'])) {
    $sort = 'ASC';
} else
    $sort = $_GET['sort'];
	
$limit      = $_GET['limit'];

$offset     = $_GET['offset'];

# Connect to PostgreSQL database
$conn = pg_connect("dbname='mydbname' user='myusername' password='mypassword' host='localhost'");
if (!$conn) {
    echo "Not connected : " . pg_error();
    exit;
}

# Build SQL SELECT statement and return the geometry as a GeoJSON element in EPSG: 4326
$sql = "SELECT " . pg_escape_string($fields) . ", st_asgeojson(transform(" . pg_escape_string($geomfield) . ",$srid)) AS geojson FROM " . pg_escape_string($geotable);
if (strlen(trim($parameters)) > 0) {
    $sql .= " WHERE " . pg_escape_string($parameters);
}
if (strlen(trim($orderby)) > 0) {
    $sql .= " ORDER BY " . pg_escape_string($orderby) . " " . $sort;
}
if (strlen(trim($limit)) > 0) {
    $sql .= " LIMIT " . pg_escape_string($limit);
}
if (strlen(trim($offset)) > 0) {
    $sql .= " OFFSET " . pg_escape_string($offset);
}
//echo $sql;

# Try query or error
$rs = pg_query($conn, $sql);
if (!$rs) {
    echo "An SQL error occured.\n";
    exit;
}

# Build GeoJSON
$output    = '';
$rowOutput = '';

while ($row = pg_fetch_assoc($rs)) {
    $rowOutput = (strlen($rowOutput) > 0 ? ',' : '') . '{"type": "Feature", "geometry": ' . $row['geojson'] . ', "properties": {';
    $props = '';
    $id    = '';
    foreach ($row as $key => $val) {
        if ($key != "geojson") {
            $props .= (strlen($props) > 0 ? ',' : '') . '"' . $key . '":"' . escapeJsonString($val) . '"';
        }
        if ($key == "id") {
            $id .= ',"id":"' . escapeJsonString($val) . '"';
        }
    }
    
    $rowOutput .= $props . '}';
    $rowOutput .= $id;
    $rowOutput .= '}';
    $output .= $rowOutput;
}

$output = '{ "type": "FeatureCollection", "features": [ ' . $output . ' ]}';
echo $output;
?>

Very good, thanks!

Nice! I think you mean ST_Transform and not transform on line 68, however?

Yes, should be ST_Transform. Wish I had read @sosso comment before I figured it out for myself.

How do you enter a Where parameter that would normally be the following in postgresql: name='bob'. I get an error when quotes are used. A query like name IS NOT NULL works.

I thought pg_escape_string($parameters) would just escape the quotes by adding extra ones before each quote. I also tried with double quotes but made no difference.

Very, very good! Many thanks!

Is there any method to do the same using jsp?

very, very good!

Thanks, this is a really helpful!

Fantástico!!

Hi all! I am new to open layers and kindly need some help. I have geojson strings saved in postgresql database table and i need to access them and add new property labels .
{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"Point","coordinates":[77.06033706665039,16.95387840270996]},"properties":{"name":"Location 1","id":0}},{"type":"Feature","geometry":{"type":"Point","coordinates":[77.09518432617188,16.960229873657227]},"properties":{"name":"Location 2","id":1}},{"type":"Feature","geometry":{"type":"Point","coordinates":[77.10479736328125,16.9808292388916]},"properties":{"name":"Location 3","id":2}},{"type":"Feature","geometry":{"type":"Point","coordinates":[77.10599899291992,16.99507713317871]},"properties":{"name":"Location 4","id":3}}]}

As the property already contains name and id fields,i want to add a new property status and remark.

You can do away with the string concatenation and directly create the feature collection with the DB query:

SELECT
  json_build_object(
    'type', 'FeatureCollection',
    'features', json_agg(ST_AsGeoJSON(t.*)::json)
  )
FROM
  my_table AS t

@see https://postgis.net/docs/ST_AsGeoJSON.html