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I ask a new question about the problem I have, because I tried it but I don't know how to solve it.

(I'm learning OpenLayers, and I see that it isn't that easy).

Using a html select, I run a PHP query and write a GeoJSON. What I can't do is how to dynamically load the resulting data and update the map every time the query is run. In a previous answer a user told me more or less how to do it, but I don't know how to apply it, if with ajax or that ...

In the HTML, I send by ajax the query I make:

<head>
<script type="text/javascript">
    $(document).ready(function() {
        $('form').submit(function(e){
            e.preventDefault();
            var data = '&parcel='+$('#parcel').val();
            $.ajax({
                type:"POST",
                dataType: "Json",
                url : "functionsPHP/obParcel.php",
                data:data,
                success:function(response){
                      if(response.ok){
                            datos = data.data;
        
                      }else{
                            alert('no data!');
                      }
                }
            });
            $("#formParcel")[0].reset();
        })
    })
    </script>
</head>
<body>
<form id="formParcel" name="parcelchooser" method="post" onSubmit="return false;">
<div class="col caja">
    <select id="parcel" name="parcel">
        <option value="">Select option...</option>
        <?php include "functionsPHP/parcels.php" ?>
    </select>
</div>
<input type="submit" value="OK" class="button"></input>
</form>
</body>

The PHP query:

require("db_config.php");
$conexion = "host=$db_host port=$db_port dbname=$db_name user=$db_user password=$db_pass";
$dbconn = pg_connect($conexion);
if (!$dbconn){
    echo "<center>Error DB conection!</center>";
    exit;
}
$parcel = $_POST['parcel'];
$parcel = str_replace("#",",",$parcel);

$query = "SELECT id, cadastralc, od, poligon, parcel, longitude,latitude, ST_AsGeoJSON(geom, 7) AS geojson FROM parcelsWHERE considered = 'Yes' AND id = '$parcel'";

$result = pg_query($dbconn, $query) or die('Query failed: ' . pg_last_error());

$rows = pg_num_rows($result);

// Mi variable de respuesta
$respuesta = array();

if ($rows != 0){
    $geojson = array(
        'type' => 'FeatureCollection',
        'features' => array()
    );
    $i = 0;
    while ($line = pg_fetch_assoc($result)) {
        $feature = array(
            'type' => 'Feature',
            'geometry' => json_decode($line['geojson'], true),
            'properties' => $data[]=$line,
            'id' => $i++
            );
        array_push($geojson['features'], $feature);
    }
    $observa = json_encode($geojson);
    $response["ok"] = true;
    $response["data"] = $observation;
    $response["menssage"] = "Send";
    $response["status"] = 200;
    $filename = "../data/parcels.json";
    $archivo = fopen($filename, "w");
    fwrite($file, $observation);
    fclose($file);
}else {
    $response["ok"] = false;
    $response["menssage"] = "No data";
    $response["status"] = 200;
}
echo json_encode($response);
pg_free_result($result);
pg_close($dbconn);

This is the script where I define the map and load the GeoJSON.

var styles = {
    'MultiPolygon': new ol.style.Style({
        stroke: new ol.style.Stroke({
          color: 'red',
          width: 3,
        }),
        fill: new ol.style.Fill({
          color: 'rgba(255, 255, 0, 1)',
        }),
    }),
};
var styleFunction = function (feature) {
    return styles[feature.getGeometry().getType()];
};
var osm = new ol.layer.Tile({
    title: "OSM",
    //baseLayer:true,
    source: new ol.source.OSM(),
    visible:true,
    displayInLayerSwitcher:true,
    preview: "images/logo_OSM.png"
});
//The @Eoin response
var vectorParcels = new ol.source.Vector({
    format: new  ol.format.GeoJSON(),
    loader: function(extent, resolution, projection) {
        var proj = projection.getCode();
        var xhr = new XMLHttpRequest();
        xhr.open('POST', "functionsPHP/obParcel.php");
        var onError = function() {
           vectorParcels.removeLoadedExtent(extent);
        }
        xhr.onerror = onError;
        xhr.onload = function() {
            xhr.responseText;
            if (xhr.status == 200) {
                vectorParcels.addFeatures(
                vectorParcels.getFormat().readFeatures(xhr.responseText));
                vectorParcels.refresh();
           } else {
             onError();
           }
         }
         xhr.send();
    },
});
var vectorlayer = new ol.layer.Vector({
    source:vectorParcels 
});
var view = new ol.View({
    projection: projection,
    zoom:5.6,
    center: [984934.497931, 5074393.544263]
});
var map= new ol.Map({
    target: 'map',
    view:view,
    layers: [osm, vectorlayer],
    controls: ol.control.defaults({
      zoom: false,
      attribution: false,
      rotate: false,
    }),
});
map.addControl (new ol.control.ScaleLine({
    units:'metric',
    minWidth:100
    })
);

var zoomslider = new ol.control.ZoomSlider();
//zoomslider.Target(document.getElementById('EP'));
map.addControl(zoomslider);
    
var zoomExt = new ol.control.ZoomToExtent({
extent: [-514454.2,4072762.7, 2856113.0,6173863.8],
    className:'ext'
})
mainbar.addControl(zoomExt);
var mousePosition = new ol.control.MousePosition({
    coordinateFormat: function(coordinates){
        var coord_x = coordinates[0].toFixed(3);
        var coord_y = coordinates[1].toFixed(3);
        return 'Lon: ' + coord_x + ' | ' + 'Lat: ' + coord_y;
    },
    projection: 'EPSG:3857',
    target: document.getElementById('myposition'),
    undefinedHTML: '&nbsp;'
});

map.addControl(mousePosition);

I'm POSTing the selected field, and I get the GeoJSON in the html form. The header that sends, for example is, parcel: 2 but that data should not be collected by (the @Eoin response) instead of sending it by the post I put in the form?

//The @Eoin response
var vectorParcels = new ol.source.Vector({
format: new  ol.format.GeoJSON(),
    loader: function(extent, resolution, projection) {
        var proj = projection.getCode();
        var xhr = new XMLHttpRequest();
        xhr.open('POST', "functionsPHP/obParcel.php");
        var onError = function() {
           vectorParcels.removeLoadedExtent(extent);
        }
... 
3
  • As per the Tour there should be only one question asked per question.
    – PolyGeo
    Jan 29 '21 at 12:43
  • How and when do you run your .php query? What does it do?
    – TomazicM
    Jan 29 '21 at 13:43
  • Just edit the question now with the ajax and the php query. I use ajax to submit the query. What I want is to update the map every time the query is run. the data is in a DB postgress and thought the best way was through a php query and write the output to a file GeoJSON.
    – user68481
    Jan 29 '21 at 14:00
1

Firstly, you want to create a new VectorSource, like this:

var vectorSource = new Vector({
  format: new GeoJSON(),
  loader: function(extent, resolution, projection) {
     var proj = projection.getCode();
     var xhr = new XMLHttpRequest();
     xhr.open('POST', "functions/parcel.php");
     var onError = function() {
       vectorSource.removeLoadedExtent(extent);
     }
     xhr.onerror = onError;
     xhr.onload = function() {
       if (xhr.status == 200) {
         vectorSource.addFeatures(
             vectorSource.getFormat().readFeatures(xhr.responseText));
       } else {
         onError();
       }
     }
     xhr.send();
   },
 });

Secondly, make a VectorLayer from this source:

var vectorlayer = new VectorLayer({
     source:vectorSource 
})

Thirdly, add this layer to the map when it gets created:

var map = new Map({
  layers: [
    new TileLayer({
      source: new OSM(),
    }),
    vectorLayer ],
  target: 'map',
  view: new View({
    center: [0, 0],
    zoom: 2,
  }),
});

If you want to see a full working example with styling, check out this link: https://openlayers.org/en/latest/examples/vector-layer.html

Just a small side note, the geoJSON specification states that ID's don't belong inside the properties on the geoJSON.

4
  • 1
    What's missing in the above answer is method for updating the layer when desired: vectorSource.refresh();
    – TomazicM
    Jan 29 '21 at 14:47
  • I have edited the question with the HTML part. It gives an error of the type: Uncaught SyntaxError: Unexpected token Q in JSON at position 0 at JSON.parse (<anonymous>) at Vg (JSONFeature.js: 191) at e.readFeatures (JSONFeature.js: 61) at XMLHttpRequest.xhr.onload (viewer.js: 311
    – user68481
    Jan 29 '21 at 16:52
  • That is not a problem with openlayers, its probably related to the PHP serving up something other than a GeoJSON. Add a console.log(xhr.responseText) to the xhr.onload function and make sure that it is a valid geoJSON.
    – Eoin
    Jan 29 '21 at 18:08
  • It doesn't receive the data that is selected in the select of the html form. How can that data be passed to the vectorSource?
    – user68481
    Feb 1 '21 at 9:25
1

The Loader wasn't receiving the data sent by Post. So, now the page where I do the query, receives the data in json format. Also I removed the vecLayer from the Map Layer Array, and added it to the map later because the vecLayer doesn't exist. I put it all in one function, and now it works. I would have to adjust map.getView (). fit (vectorParcels.getExtent ()); because it zooms in too big for me, if the polygon thant I want to visualize is large, it doesn't grab into the map container div.

obParcel.php:

...
$params = json_decode(file_get_contents('php://input'), true);
$parcel = $params["parcel"];
...

scriptMap:

function drawParcel(parcelId){
    var vectorParcels = new ol.source.Vector({
        format: new  ol.format.GeoJSON(),
        loader: function(extent, resolution, projection) {
            var proj = projection.getCode();
            var url = "functionsPHP/obParcel.php"
            var xhr = new XMLHttpRequest();

            var params = {
                parcel: parcelId
            }

            xhr.open('POST', url);
            xhr.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
            var onError = function() {
               vectorParcels.removeLoadedExtent(extent);
            }
            xhr.onerror = onError;
            xhr.onload = function() {
                xhr.responseText;
                console.log(xhr.responseText);
                if (xhr.status == 200) {
                    vectorParcels.addFeatures(
                    vectorParcels.getFormat().readFeatures(xhr.responseText));
                    map.getView().fit(vectorParcels.getExtent());
                    $("#formParcel")[0].reset();
               } else {
                 onError();
               }
             }
             xhr.send(JSON.stringify(params));
        },
    });
    var vectorlayer = new ol.layer.Vector({
        source:vectorParcels,
        visible:true,
        displayInLayerSwitcher: false,
        style: styleFunction,               
    });

    map.addLayer(vectorlayer)
}

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