Transfer format between geodatabase and OpenLayers

Question

I was curious ab your opinions whats the most efficient transfer format between SpatiaLite and OpenLayers. Currently Im developing an application based on SpatiaLite (extension of SQLite) and OpenLayers and as a transfer format I use GeoJSON.

My procedure: 1) quering DB by php script, using SpatiaLite's function AsGeoJSON, thus obtaining geojson formatted data

2) using php's print() to transfer retrieved data from php variable to JS variable:

$result = $db->query($query);

$r = '{"type": "FeatureCollection","features": [';
while($row = $result->fetchArray(SQLITE3_ASSOC))
{
  $r .= '{"type":"Feature","properties":{}, "geometry":' . $row['geometry'] . '},';
}
$r .= ']}';
print'<script> CadastreBorder = ' . $r . '; </script>';

3) creating the features for Vector Layer in OpenLayers by reading

var vectorLayer = new OpenLayers.Layer.Vector(name, {style: style, rendererOptions:
{zIndexing: true}});
var formatGeoJSON = new OpenLayers.Format.GeoJSON({});
vectorLayer.addFeatures(formatGeoJSON.read(CadastreBorder));
map.addLayer(vectorLayer);

Is there any way how to achieve the same goal more efficiently and more nicely? Thanks!

Answer 1

Not sure about speed, but if you're using recent version of PHP (5.2 >=) you'd might consider using json_encode on php's arrays. Instead of creating string you'd create an array looking somewhere like this:

$geoJSON_array = Array(
    "type" => "FeatureCollection",
    "features" => Array()
    );

And for each row of geometry, add new table to "features":

Array(
    "type" => "Feature",
    "properties" => Array(),
    "geometry" => Array(... your geometry),
)

After creating such array, run json_encode over it and you're home. For safety I'd check it validates (e.g. using http://geojsonlint.com/). This may help you later on, when e.g. there would be need to support new information, or to add new kinds of elements to the map.

Question: Why are you not using fixed strategy for loading points? If you're creating this geoJSON to file/as script, you may also tell openlayers to download it automatically, likes this:

var vectorLayer = new OpenLayers.Layer.Vector(name, {
    strategies: [new OpenLayers.Strategy.Fixed()],
    protocol: new OpenLayers.Protocol.HTTP({
        url: "json/my_geojson.json",
        format: new OpenLayers.Format.GeoJSON()
    }),
    style: style,
    rendererOptions: {zIndexing: true}
});