[GIS] OpenLayers – How to construct OpenLayers.Bounds

openlayers-2

I would like to create Bounds for a layer but I am not sure in what order I have to provide the min_x / max_x and min_y / max_y coordinates.

is it correct to put it in that order: min_y, min_x, max_y, max_x

var bounds = new OpenLayers.Bounds.fromArray([{{ wms.min_y }}, {{ wms.min_x }}, {{ wms.max_y }}, {{ wms.max_x }}, ]);

Best Answer

The documentation for the Bounds constructor says:

bounds {Array(Number)} [left, bottom, right, top]

So you need to provide these parameters as numbers

var bounds = new OpenLayers.Bounds.fromArray([wms.min_x, wms.min_y, wms.max_x, wms.max_y]);

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[GIS] How to provide transform information to openlayers on Image layer

Just assigning a projection to an image won't cut it, as you can tell you're 700km east of the prime meridian. You will need to know either:

The top left corner and the metres per pixel of the image in the EPSG:900913 projection (you should use the equivalent EPSG:3857 these days).
If the image is originally in a different projection, the bounds of the image in that projection.

I assume you don't know the first (otherwise you wouldn't be asking the question!), and if it is the latter, you will need to assign the projection and bounds in your source projection before warping it.

For instance, if your image is in the unprojected WGS84 coordinate system (EPSG:4326), you'd use something like:

gdal_translate -of "PNG" -a_srs EPSG:4326 -a_ullr <coordinates of the image bounds> src_file file_out_a

This will produce an XML file with the georeference coordinates similar to the one you posted but in degrees rather than metres. Next use gdal_warp:

gdalwarp -t_srs EPSG:3857 -of "PNG" file_out_a file_out_b

It is likely you'll get black borders around your new image because a square on a spheroid doesn't map to a square on a plane. So you will need to think about mask layers or nodata values.

[GIS] Modify existing library from OpenLayers (ZoomToMaxExtent)

You don't need to change the OpenLayers code. Instead, add the bounds to your map's options:

var options = {
  maxExtent: new OpenLayers.Bounds(-16.08,49.06,6.76,58.74),
  maxResolution: 0.00138671875,
  projection: "EPSG:4326",
  units: "degrees"
};
map = new OpenLayers.Map("map", options);

Best Answer

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[GIS] How to provide transform information to openlayers on Image layer

[GIS] Modify existing library from OpenLayers (ZoomToMaxExtent)

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