Edit in JSFiddle

function go() {
    proj4.defs('EPSG:4559',
    '+proj=utm +zone=20 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs') ;
    var map = new ol.Map({
        target: 'map',
        layers: [
            new ol.layer.GeoportalWMTS({
                layer: "ORTHOIMAGERY.ORTHOPHOTOS",
                olParams: {
                    opacity: 0.7
                }
            })
        ],
        view: new ol.View({
            center: [-6852598, 1832310],
            zoom: 12
        })
    });    
    var mpControl = new ol.control.GeoportalMousePosition({
        collapsed: false,
        systems : [
            {
                crs : 'EPSG:4559',
                label : "UTM 20 Nord",
                type : "Metric"
            },
            {
                crs : "EPSG:4326",
                label : "Géographiques",
                type : "Geographical"
            }
        ],
        units : ["DEC","M"]
    });
    map.addControl(mpControl);
}

Gp.Services.getConfig({
    apiKey: "essentiels",
    onSuccess: go
});

var infoDiv = document.getElementById("info");
infoDiv.innerHTML = "<p> Extension OL version " + Gp.olExtVersion + " (" + Gp.olExtDate + ")</p>";

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

#map {
    padding: 5px;
    width: 100%;
    height: 300px;
    box-shadow: 0 0 10px #999;
}

#info {
    padding: 5px;
    width: 100%;
    height: 20px;
    font-family: "monospace";
    font-size: 10px;
}