I have also created an interim solution until the API catches up:// Use the hosted 10.1 Beta ArcGIS Server Geometry Service
gsvc = new esri.tasks.GeometryService("http://servicesbeta4.esri.com/arcgis/rest/services/Geometry/GeometryServer");
// create a new point from the geolocation location
var point = new esri.geometry.Point(
location.coords.longitude, location.coords.latitude,
new esri.SpatialReference({
wkid: 4326
})
);
// set the output spatial reference for the project method
var outSR = new esri.SpatialReference({
wkid: 27700
});
// tack on two parameters in the query object - these will be added to the url and will give us a more accurate transformation
gsvc._url.query = dojo.mixin(gsvc._url.query, {
// set the datum transformation to OSGB_1936_To_WGS_1984_Petroleum (1314)
// the options are listed here: http://servicesbeta2.esri.com/arcgis/sdk/rest/dattrans.html
transformation: 1314,
// we are transforming backwards in this case
// FROM WGS84 TO OSGB36
transformForward: false
});
// call the geometry service project method as you would normally
gsvc.project([point], outSR, function (projectedPoints) {
// get the projected point
pt = projectedPoints[0];
// add it to the map
addGraphic(pt);
// zoom the map to the added point
map.centerAndZoom(pt, 17);
});