Apakah ada cara mudah untuk menggunakan Postgis GeoJSON di Openlayers 3

Saya menggunakan google-vector-layers dan leaflet-vector-layers dari Jason Sanford ( https://github.com/JasonSanford ) untuk dengan mudah menampilkan, menata, dan menambahkan popup yang dapat dikustomisasi untuk data dari database Postgis. Ini bekerja dalam kombinasi dengan versi PHP-Database-GeoJSON yang dimodifikasi dari Bryan McBride.

Apakah tidak ada yang sebanding dengan Openlayers 3 di luar sana? Saya harus mengakui, bahwa saya tidak memiliki keterampilan pemrograman untuk menulis perpustakaan seperti itu. Mungkin ada yang tahu tentang kode yang sebanding. Setelah melakukan banyak Googling di sekitar, saya menemukan banyak jawaban untuk masalah tertentu dan berhasil menerapkan hal-hal tentang cara memuat GeoJSON menggunakan strategi Ajax dan boundingBox, menata layer vektor dan menambahkan popup, tapi saya masih kehilangan yang mudah cara bagaimana menyatukan semua hal ini.

Saya bertanya-tanya apakah mungkin ada solusi yang ada yang belum saya temukan sampai hari ini, karena saya pikir PostGis> GeoJSON> Openlayers 3 (termasuk styling dan fitur tampilan melalui popup) harus menjadi cara yang cukup standar?

Karena tidak ada jawaban untuk pertanyaan saya, saya mencoba untuk terinspirasi oleh kode lain yang sudah ada, dan terus mengembangkan GeoJSON-constructor dasar di openlayers 3, yang memenuhi kebutuhan saya.

Saya sebenarnya bisa

• memuat lapisan yang berbeda dari PostGIS dengan meneruskan nama-tabel, bidang-tabel dan klausa WHERE (dengan semua kemungkinan keajaiban PosgreSQL / PostGis)
• gaya mereka (menggunakan nilai tunggal, unik atau rentang)
• perlihatkan / sembunyikan layer di min / maxResolution
• pengidentifikasi unik harus id untuk mencegah fitur dimuat beberapa kali
• lapisan dimuat melalui strategi ol.loadingstrategy.bbox sehingga hanya data yang terlihat dimuat
• mendefinisikan popup-templat khusus lapisan
• tambahkan pelabelan khusus lapisan

Jadi ini sudah merupakan paket lucu, yang dapat diadaptasi (dan ditingkatkan) dengan sangat mudah. Karena itu saya ingin membagikan kodenya di sini. Keseluruhan terdiri dari tiga bagian:

• ol3Vector.js kelas yang diperluas dari ol.layer.Vector
• file map.js di mana peta dan semua layer didefinisikan
• file get_geojson.php yang digunakan di sisi server untuk membangun sql-string dan mengembalikan GeoJSON yang valid.

Agar dapat bekerja dengan benar, ol3Vector.js perlu dimuat terlebih dahulu. Ini kodenya:

 // class to load vector layers from Postgis using a modified php-script from
 // Bryan McBride
 // https://github.com/bmcbride/PHP-Database-GeoJSON 
 //
 ol3Vector = function(options) {

 //
 // -------- Defining default style settings ----------
 //
 var fill = new ol.style.Fill({
    color: 'rgba(255,255,255,0.4)'
 });
 var stroke = new ol.style.Stroke({
    color: '#3399CC',
    width: 1.25
 });
 var text = new ol.style.Text({
    text: "",
    font: "16px Calibri,sans-serif",
    fill: new ol.style.Fill({
        color: [255, 255, 255, 1]
    }),
    stroke: new ol.style.Stroke({
        color: [0, 0, 0, 1],
        width: 2.5
    })
});

var image = new ol.style.Circle({  // actually point styling only works with image, and not with icons
    fill: fill,
    stroke: stroke,
    radius: 5
});

var style = new ol.style.Style({
    image: image,
    fill: fill,
    stroke: stroke,
    text: text
});

var styles = [style];

//
// ------------- defining options to build the new ol3Vector-layer -----------
//
var options = {
    title: options.title,
    visible: false,
    geotable: options.geotable,  // table name in PostGis-database
    fields: options.fields,      // field-names
    where: options.where,        // where-string passed to PostGis
    source: new ol.source.Vector({
        projection: "EPSG:4326",
        attributions: [new ol.Attribution({
            html: options.attribution
        })],
        strategy: ol.loadingstrategy.bbox,   //load only data off the visible map
        loader: function(extent, resolution, projection) {
            var extent = ol.proj.transformExtent(extent, projection.getCode(), ol.proj.get('EPSG:4326').getCode());
            $.ajax({
                type: "GET",
                dataType: "json",
                url: "./mapdata/get_geojson.php?" +     // define path to the get_geojson.php script
                    "geotable=" + options.geotable +
                    "&fields=" + options.fields +
                    "&where=" + options.where +
                    "&bbox=" + extent.join(","),
                context: this
            }).done(function(data) {
                var format = new ol.format.GeoJSON();
                this.addFeatures(format.readFeatures(data, {
                    dataProjection: "EPSG:4326",
                    featureProjection: "EPSG:3857"
                }));

            });

        }
    }),
    minResolution: options.minResolution,
    maxResolution: options.maxResolution,
    content: options.content,
    symbology: options.symbology,
    showLabels: options.showLabels,
    label: options.label,
    style: (function label_style() { // style function needed to be wrapped in a function to get it work
        // ------ labeling -----------
        var layerLabel = "";
        if (!options.showLabels) {
            layerLabel = "";
        } else if (options.showLabels) {
            layerLabel = options.label;
        }
        return function(feature, resolution) {
            style.getText().setText(feature.get(layerLabel));

            // ------ styling -------------
            if (!options.symbology) {
                return style;
                //            return false;        
            } else if (options.symbology) {

                var atts = feature.getProperties();

                switch (options.symbology.type) {
                    case "single":
                        // Its a single symbology for all features so just set the values for fill and stroke
                        //
                        switch (feature.getGeometry().getType()) {
                            case "Point":
                            case "MultiPoint":

                                style.image = style.getImage().getFill().setColor(options.symbology.styleOptions.fill);
                                style.image = style.getImage().getStroke().setColor(options.symbology.styleOptions.color);
                                style.image = style.getImage().getStroke().setWidth(options.symbology.styleOptions.width);
                                style.image = style.getImage().setRadius(options.symbology.styleOptions.radius);
                                break;

                            case "LineString":
                            case "MultiLineString":
                            case "Polygon":
                            case "MultiPolygon":

                                style.fill = style.setFill(new ol.style.Fill({
                                    color: options.symbology.styleOptions.fill
                                }));
                                style.stroke = style.setStroke(new ol.style.Stroke({
                                    color: options.symbology.styleOptions.color,
                                    width: options.symbology.styleOptions.width
                                }));
                                break;
                        }
                        break;

                    case "unique":
                        // Its a unique symbology. Check if the features property value matches that in the symbology and style accordingly
                        // 
                        var att = options.symbology.property;
                        for (var i = 0, len = options.symbology.values.length; i < len; i++) { // field with values to define styles
                            if (atts[att] == options.symbology.values[i].value) { // unique value to identify style
                                for (var key in options.symbology.values[i].styleOptions) {

                                    switch (feature.getGeometry().getType()) {
                                        case "Point":
                                        case "MultiPoint":

                                            style.image = style.getImage().getFill().setColor(options.symbology.values[i].styleOptions.fill);
                                            style.image = style.getImage().getStroke().setColor(options.symbology.values[i].styleOptions.color);
                                            style.image = style.getImage().getStroke().setWidth(options.symbology.values[i].styleOptions.width);
                                            style.image = style.getImage().setRadius(options.symbology.values[i].styleOptions.radius);
                                            break;

                                        case "LineString":
                                        case "MultiLineString":
                                        case "Polygon":
                                        case "MultiPolygon":

                                            style.fill = style.setFill(new ol.style.Fill({
                                                color: options.symbology.values[i].styleOptions.fill
                                            }));
                                            style.stroke = style.setStroke(new ol.style.Stroke({
                                                color: options.symbology.values[i].styleOptions.color,
                                                width: options.symbology.values[i].styleOptions.width
                                            }));
                                            break;
                                    }
                                }
                            }
                        }
                        break;

                    case "range":
                        // Its a range symbology. Check if the features property value is in the range set in the symbology and style accordingly
                        //
                        var att = options.symbology.property;
                        for (var i = 0, len = options.symbology.ranges.length; i < len; i++) {
                            if (atts[att] >= options.symbology.ranges[i].range[0] && atts[att] <= options.symbology.ranges[i].range[1]) {
                                for (var key in options.symbology.ranges[i].styleOptions) {

                                    switch (feature.getGeometry().getType()) {
                                        case "Point":
                                        case "MultiPoint":

                                            style.image = style.getImage().getFill().setColor(options.symbology.ranges[i].styleOptions.fill);
                                            style.image = style.getImage().getStroke().setColor(options.symbology.ranges[i].styleOptions.color);
                                            style.image = style.getImage().getStroke().setWidth(options.symbology.ranges[i].styleOptions.width);
                                            style.image = style.getImage().setRadius(options.symbology.ranges[i].styleOptions.radius);
                                            break;

                                        case "LineString":
                                        case "MultiLineString":
                                        case "Polygon":
                                        case "MultiPolygon":

                                            style.fill = style.setFill(new ol.style.Fill({
                                                color: options.symbology.ranges[i].styleOptions.fill
                                            }));
                                            style.stroke = style.setStroke(new ol.style.Stroke({
                                                color: options.symbology.ranges[i].styleOptions.color,
                                                width: options.symbology.ranges[i].styleOptions.width
                                            }));
                                            break;
                                    }
                                }
                            }
                        }

                        break;
                }
            }
            return styles;
        }
    })()
}

ol.layer.Vector.call(this, options);

};

ol.inherits(ol3Vector, ol.layer.Vector);

di sini contoh map.js

function init() {
document.removeEventListener('DOMContentLoaded', init);

//
// ------- Layers and Map ----------------
//
var baselayers = new ol.layer.Group({  
    title: 'Baselayers',
    layers: [
        new ol.layer.Tile({
            title: 'OSM',
            type: 'base',
            visible: true,
            source: new ol.source.OSM()
        })
    ]
});

var toplayers = new ol.layer.Group({
    title: 'Toplayer',
    layers: []
});


var view = new ol.View({
    center: ol.proj.fromLonLat([6.2, 49.6]),
    zoom: 12
});

var popup_div = document.getElementById('popup');
var popup = new ol.Overlay({
    element: popup_div,
    positioning: 'bottom-center',
    stopEvent: false
});

var map = new ol.Map({
    target: 'map',
    view: view,
    controls: ol.control.defaults().extend([
        new ol.control.Zoom(),
        new ol.control.FullScreen(),
        new ol.control.ZoomSlider(),
        new ol.control.LayerSwitcher({  //layergroups are used with the layerswitcher from https://github.com/walkermatt/ol3-layerswitcher
            tipLabel: 'Layer Switcher'
        }),
        new ol.control.OverviewMap(),
        new ol.control.ScaleLine()
    ]),
    overlays: [popup],
    layers: [baselayers, toplayers],
    interactions: ol.interaction.defaults().extend([
        new ol.interaction.Select({
            layers: [baselayers, toplayers]
        })
    ])
});

//
// ------------ define toplayers -------------------
//
var n2k_dh_l = new ol3Vector({
    title: "Natura 2000 Habitats Directive",   // name of the layer to show up in the layerswitcher
    attribution: "<br />Réseau Natura 2000 Habitats Directive",
    geotable: "n2k_dh",
    fields: "gid as id, sitecode, sitename, surfha",
    where: "sitename ilike '%moselle%'",    // You can use all the PostgreSQL or PostGis features here
    symbology: {
        type: "single",
        styleOptions: {
            fill: "rgba(100,250,0,0.1)",   // define colors as rgba()
            color: "green",                // or simple color-names
            width: 2
        }
    },
    minResolution: 0.01,
    maxResolution: 50,
    content: "<p><strong> BH {sitecode}</strong><hr>{sitename}<br />{surfha} ha </p>",
    showLabels: true,    // show labels on map
    label: "sitename"    // field used for labeling
});

var n2k_do_l = new ol3Vector({
    title: "Natura 2000 Birds Directive",
    attribution: "<br />Réseau Natura 2000 Birds Directive",
    geotable: "n2k_do",
    fields: "gid as id, sitecode, sitename, surfha",
    where: "",
    symbology: {
        type: "single",
        styleOptions: {
            fill: "rgba(100,250,0,0.1)",
            color: "magenta",
            width: 2
        }
    },
    minResolution: 0.01,
    maxResolution: 50,
    content: "<p><strong> BD {sitecode}</strong><hr>{sitename}<br />{surfha} ha </p>",
    showLabels: true,
    label: "sitecode"
});

var communes = new ol3Vector({
    map: map,
    title: "Communes",
    attribution: "<br />Communes",
    geotable: "communes",
    fields: "gid as id, surfha, commune, stats",
    where: "",
    symbology: {
        type: "unique",
        property: "stats",  // field used to style depending on their value
        values: [{
                value: "AB", 
                styleOptions: {
                    fill: "rgba(0,0,0,0.0)",
                    color: "grey",
                    width: 1.25
                }
            },
            {
                value: "CD",
                styleOptions: {
                    fill: "rgba(100,250,0,0.1)",
                    color: "green",
                    width: 2
                }
            },
            {
                value: "",
                styleOptions: {
                    fill: "rgba(250,0,0,0.1)",
                    color: "red",
                    width: 2
                }
            }
        ]
    },
    minResolution: 0.01,
    maxResolution: 50,
    content: "<p><strong>{commune}</strong><hr>{stat}<br />{surfha} ha </p>",
    showLabels: true,   
    label: "commune"    
});

var n2k_dh_r = new ol3Vector({
    map: map,
    title: "Natura 2000 Habitats Directive - site size",
    attribution: "<br />Réseau Natura 2000 Habitats Directive",
    geotable: "n2k_dh",
    fields: "gid as id, sitecode, sitename, surfha",
    where: "",
    symbology: {
        type: "range",
        property: "surfha", // field that holds values that should be displayed as ranges
        ranges: [{
            range: [1, 100], // defining range min and max values of property field
            styleOptions: {
                fill: "rgba(220,20,60,0.3)",
                color: "crimson",
                width: 1
            }
        }, {
            range: [101, 1000],
            styleOptions: {
                fill: "rgba(255,165,0,0.3)",
                color: "orange",
                width: 1
            }
        }, {
            range: [1001, 10000],
            styleOptions: {
                fill: "rgba(255,255,0,0.3)",
                color: "Yellow",
                width: 1
            }
        }]
    },
    minResolution: 0.01,
    maxResolution: 50,
    content: "<p><strong> BH {sitecode}</strong><hr>{sitename}<br />{surfha} ha </p>",
    showLabels: true,
    label: "sitecode"
});

var btk_p = new ol3Vector({
    map: map,
    title: "Habitats points",  // point layers
    attribution: "<br />Cartho",
    geotable: "btk_p",
    fields: "gid as id, btyp1_code, btyp1_name, cs",
    where: "",
    symbology: {
        type: "unique",
        property: "cs",
        values: [{
                value: "A", 
                styleOptions: {
                    fill: "rgba(0,128,0,0.3)",
                    color: "rgba(0,128,0,0.3)",
                    width: 1,
                    radius: 20 // must be set in order to render point features    
                }
            },
            {
                value: "B",
                styleOptions: {
                    fill: "rgba(255,165,0,0.3)",
                    color: "rgba(255,165,0,0.3)",
                    width: 1,
                    radius: 15
                }
            },
            {
                value: "C",
                styleOptions: {
                    fill: "rgba(255,0,0,0.3)",
                    color: "rgba(255,0,0,0.3)",
                    width: 1,
                    radius: 10
                }
            }
        ]
    },
    minResolution: 0.01,
    maxResolution: 50,
    content: "<p><strong>{btyp1_code}</strong><hr>{btyp1_name}<br />{cs}</p>",
    showLabels: false,
    label: "bewertung1"
});

// ------------------ add ol3Vectors to toplayers ----------
// 
toplayers.setLayers(new ol.Collection([n2k_do_l, n2k_dh_l, communes, n2k_dh_r, btk_p]));
//
// ------------------ show popups based on content-template for different layers --------------------
//  
map.on('click', function(evt) {
    var feature = map.forEachFeatureAtPixel(evt.pixel,
        function(feature, layer) {
            return feature;
        });
    var popupContent = map.forEachLayerAtPixel(evt.pixel,
        function(layer) {
            return layer.get('content');
        });
    if (feature) {
        popup.setPosition(evt.coordinate);
        var atts = feature.getProperties();
        for (var prop in atts) {
            var re = new RegExp("{" + prop + "}", "g");
            popupContent = popupContent.replace(re, atts[prop]);
        }
        $(popup_div).attr('data-placement', 'auto');
        $(popup_div).attr('data-content', popupContent);
        $(popup_div).attr('data-html', true);
        $(popup_div).popover();
        $(popup_div).popover('show');
        $('.popover-title').click(function() {
            $(popup_div).popover('destroy');
        });
    } else {
        $(popup_div).popover('destroy');
    }
});
} // End function init()
document.addEventListener('DOMContentLoaded', init);

Akhirnya kita membutuhkan get_geojson.php untuk mengambil data dari database PostGis.

<?php
/**
 * GET GeoJSON from PostGIS
 * Query a PostGIS table or view and return the results in GeoJSON format, suitable for use in OpenLayers, Leaflet, etc.
 * Author:  Bryan R. McBride, GISP, adapted by G.Moes
 * Contact: bryanmcbride.com
 * GitHub:  https://github.com/bmcbride/PHP-Database-GeoJSON
 * 
 * @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: 2169 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       integer     $precision      digits of returned geojson 6 = 0.111 m submeter as DEFAULT *OPTIONAL*
 * @param       real        $simplify       simplify geometry to >5.0m as DEFAULT *OPTIONAL*  
 * @param       string      $offset         Offset used in conjunction with limit *OPTIONAL*
 * @return      string                  resulting geojson string
 */


# Connect to PostgreSQL database You need to pass here the credentials to connect to Your database
require("../database/connect.php");


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'])) {
    $geomfield='the_geom';
} else
    $geomfield = $_GET['geomfield'];
if (empty($_GET['srid'])) {
    $srid = 2169;    // changethis if You need another standard SRID
} else
    $srid = $_GET['srid'];
if (empty($_GET['fields'])) {
    $fields = '*';
} else
    $fields = $_GET['fields'];
$parameters = $_GET['where'];
$bbox = $_GET['bbox'];
if (empty($_GET['precision'])) {
    $precision = 6;    // change this to Your needs
} else
    $precision = $_GET['precision'];
if (empty($_GET['simplify'])) {
    $simplify = 5.0;   // change this to Your needs
} else
    $simplify = $_GET['simplify'];    
$orderby    = $_GET['orderby'];
if (empty($_GET['sort'])) {
    $sort = 'ASC';
} else
    $sort = $_GET['sort'];
$limit      = $_GET['limit'];
$offset     = $_GET['offset'];



# Build SQL SELECT statement and return the geometry as a GeoJSON element in EPSG: 4326
$sql = "SELECT " . pg_escape_string($fields) . ", st_asgeojson(st_transform(ST_SimplifyPreserveTopology(" . pg_escape_string($geomfield) . ",".$simplify."),4326),".$precision.") AS geojson FROM " . pg_escape_string($geotable);
if (strlen(trim($parameters)) > 0) {

      $sql .= " WHERE " . str_replace("''", "'", pg_escape_string($parameters));
}
if (strlen(trim($parameters)) > 0 AND strlen(trim($bbox)) > 0){
     $sql .= " AND the_geom &&  st_transform(st_makeenvelope(".pg_escape_string ($bbox).",4326),".$srid.")";
}
if (strlen(trim($parameters)) <= 0 AND strlen(trim($bbox)) > 0) {
      $sql .= " WHERE the_geom &&  st_transform(st_makeenvelope(".pg_escape_string ($bbox).",4326),".$srid.")";
}
if (strlen(trim($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
$rs = pg_query($db_handle, $sql);
if (!$rs) {
    echo "An SQL error occured.\n";
    echo $sql;
    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 . ' ]}';

header('Content-type:application/json;charset=utf-8');
echo json_encode( $output);
?>

Selamat bersenang-senang! Semoga ini membantu seseorang untuk melangkah lebih jauh atau meningkatkan kode ini dan saya akan menerbitkannya di GitHub.