How to load Global Multi-Resolution Topography (GMRT) Web Map Service (WMS) in openlayers?

0
votes

I'm trying to load the Global Multi-Resolution Topography (GMRT) WMS into an openlayers map using OpenStreetMap (OSM) as base layer. The URL for the GMRT webservice is: https://www.gmrt.org/services/mapserver/wms_merc?

The code I'm trying is:

<!DOCTYPE html>
<html lang="en">
<head>
    <link rel="stylesheet" href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" type="text/css">
    <style>
        .map {
            height: 400px;
            width: 100%;
        }
    </style>

    <script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>

    <title>OpenLayers example</title>

</head>

<body>

<h2>My Map</h2>

<div id="map" class="map"></div>

<script type="text/javascript">
    var map = new ol.Map({
        target: 'map',
        layers: [
            new ol.layer.Tile({
                source: new ol.source.OSM()
            }),
            new ol.layer.Image({
                source: new ol.source.ImageWMS({
                    url: 'https://www.gmrt.org/services/mapserver/wms_merc?'
                })
            })
        ],
        view: new ol.View({
            center: ol.proj.fromLonLat([37.41, 8.82]),
            zoom: 4
        })
    });
</script>

</body>
</html>

The code does not output the GMRT layer, but only the base layer with OSM in it.

When scanning through the connections established by the browser, I find a successful request to www.gmrt.org:

GEThttps://www.gmrt.org/services/mapserver/wms_merc?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&FORMAT=image%2Fpng&TRANSPARENT=true&CRS=EPSG%3A3857&STYLES=&WIDTH=1235&HEIGHT=600&BBOX=-1873624.4373262404%2C-1947003.9844800094%2C10209540.993994422%2C3923359.7878215266
[HTTP/1.1 200 OK 343ms]

SERVICE WMS
VERSION 1.3.0
REQUEST GetMap
FORMAT  image/png
TRANSPARENT true
CRS EPSG:3857
STYLES  
WIDTH   1235
HEIGHT  600
BBOX    -1873624.4373262404,-1947003.9844800094,10209540.993994422,3923359.7878215266

I've checked this post, which appears to be a similar problem, and also looked at the GetCapabilities, but the returned XML doesn't say a lot to me.

Any ideas of what I'm doing wrong? I'm new to openlayers, so I'd appreciate as much detail as possible.

1
openlayers

1 Answers

1
votes

ImageWMS and TileWMS always need a params option to specify the WMS LAYERS parameter

source: new ol.source.ImageWMS({
    url: 'https://www.gmrt.org/services/mapserver/wms_merc?',
    params: { 'LAYERS': 'GMRT' }
})