Is is possible to get the center (or extent) of an XYZ source in Openlayers? (I am not talking about getting the center of a view, but obtaining the center of the map defined by the source itself.) The VectorSource does have a getExtent function, but unfortunately XYZ has no such method.
Using source.getTileGrid().getExtent() unfortunately does not seem to work; here is a minimal reproducible example:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8"/>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/ol.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/ol.css">
</head>
<body>
<div id="map" class="map"></div>
<script type="text/javascript">
const src = new ol.source.XYZ({
url: 'https://s3.eu-central-1.amazonaws.com/old-maps/the-hague-1944/tiles/{z}/{x}/{y}.jpg'
})
const ext = src.getTileGrid().getExtent();
console.log(ext);
</script>
</body>
</html>
(I used this map.)
This returns [-20037508.342789244, -20037508.342789244, 20037508.342789244, 20037508.342789244] as if the center was [0, 0, 0, 0]. Which is of course not the case and if I used a different map, the result was the exact same extent.
2
Your code uses the default global tile grid and will attempt to load tiles anywhere in the world at any zoom level. Unless you are ablw to run the script
# Get the geographic coordinates of the file's left top and right bottom
lt = mercantile.lnglat(gt[0], gt[3])
rb = mercantile.lnglat(gt[0] + (ds.RasterXSize * gt[1]),
gt[3] + (ds.RasterYSize * gt[5]))
you would need to use a test map to see where tiles are being loaded and a which zoom levels, by overlaying it with a TileDebug layer. That shows tiles are available from zoom levels 10 to 16, and at level 16 X values range from 33503 to 33583 and Y values from 21602 to 21655.
With that information you can set up a constrained tile grid where only valid tiles should be requested:
const tilegrid = ol.tilegrid.createXYZ({maxZoom: 16});
const extent = ol.extent.createEmpty();
ol.extent.extend(extent, tilegrid.getTileCoordExtent([16, 33504, 21602]))
ol.extent.extend(extent, tilegrid.getTileCoordExtent([16, 33583, 21655]))
const src =new ol.source.XYZ({
url: 'https://s3.eu-central-1.amazonaws.com/old-maps/the-hague-1944/tiles/{z}/{x}/{y}.jpg',
tileGrid: new ol.tilegrid.TileGrid({
origins: tilegrid.getResolutions().map((r, i) => tilegrid.getOrigin(i)),
resolutions: tilegrid.getResolutions(),
tileSizes: tilegrid.getResolutions().map((r, i) => tilegrid.getTileSize(i)),
minZoom: 10,
extent: extent,
})
});
The extent will be in EPSG:3857 coordinates, you could use transformExtent to convert to LonLat if you need to.
4