Elevation Correction for WGS84 - 4326 GeoJSON Displaying at Correct Height

Question

GeoJSON data being displayed on the Map with a renderer for a 3D Line Symbol as a Path.

I am assuming the elevation of the Map is using `absolute-height`, but my 4326 data is showing up still too far below the earth. From my understanding, the height I have is from the ellipsoid of the 4326 datum. So, why is it not getting displayed correctly on the ArcGIS Map?

const map = new ArcGISMap({
    basemap: 'hybrid',
    ground: 'world-elevation',
});

const view = new SceneView();
view.spatialReference = SpatialReference.WGS84;

const renderer = new SimpleRenderer({
    symbol: new LineSymbol3D({
      symbolLayers: [
        new PathSymbol3DLayer({
          profile: 'circle',
          width: 0.508,
          material: { color: [255, 75, 75] },
        }),
      ],
    }),
});

const geoJSONLayer = new GeoJSONLayer();
const url = "..."
geoJSONLayer.url = url;
geoJSONLayer.outFields = ['*'];
geoJSONLayer.renderer = renderer;
map.add(geoJSONLayer);

GreteSoosalu · Answer

Looks like the elevation difference we see is because the data and the elevation model are in different vertical datums.

For the US, Esri provides a 3D elevation service based on USGS data, which is using a vertical datum of NAVD 88. This means the elevation values are orthometric (i.e. based on mean sea level).

As you’ve mentioned, your data uses 4326 ellipsoid datum, so you would need to convert the coordinates accordingly (usually GPS units should be able to do that).

Hope this helps!

PS: here are some related resources:

* ArcGIS blog: Introducing Esri’s World Elevation Services  - mentions that the heights coming from terrain service are orthometric 
* List of datasets used for the World Elevation service - note that Terrain 3D related datasets are listed under Topography
* USGS: Why don't the elevations on your maps agree with those provided by my GPS system?
* ArcGIS Pro: Vertical datums

developerarce · Answer

Yes, the feature should be about 2ft below the surface.

GreteSoosalu · Answer

Thanks for the codepen!

The ground elevation value at the area of the feature is about 340m (same when checking the location with https://apps.nationalmap.gov/viewer/ elevation tool) i.e. 30m above your feature.

Do you know approx. how many feet/meters below the ground the feature should be?