PNG Overlay not correct using L.CRS.EPSG3857 projection

Question

I am using leaflet and openstreet maps. I created a png using EPSG3857 however the image is not laying correctly on the map.

if you look at the Baja Region and Florida you will see the data on land. The data should be over the water not the land.

 var map = L.map('map', { editable: true },{crs: L.CRS.EPSG3857}).setView(initialCoordinates , initialZoom),   
 tilelayer =
    L.tileLayer(url_tile,
        {
            noWrap: true,
            maxZoom: 12, minZoom: 2, attribution: 'Data \u00a9 <a href="https://www.openstreetmap.org/copyright"> OpenStreetMap Contributors </a> Tiles \u00a9 HOT'
        }).addTo(map);

var overlay_image = 'images/webmercator-google.png';
imageBounds = [[-90, -180], [90, 180]];
L.imageOverlay(overlay_image, imageBounds, { opacity: 0.8 }).addTo(map);

Answer 1

When using EPSG:3857, Leaflet clamps all latitude data to +/-85.05° (or, to be precise, +/-20037508.34 on the EPSG:3857 Y coordinate). This is done to prevent data appearing outside of the coverage area of default EPSG:3857 tiles.

To illustrate this, consider the following bit of code:

for (var i=83; i<90; i+=0.1) {
    L.marker([i, i]).addTo(map);
}

That should (naïvely) display a lot of markers in a diagonal-ish line. But when actually doing that, the result looks like:

See how the markers don't go north of the 85.01° parallel, and how that fits the limit of tiles (blue sea versus grey out-of-map background).

Remember, EPSG:3857 and any other (non-traverse, non-oblique) cylindrical projections cannot display the north/south poles because they get projected to an infinite Y coordinate.

---

OK, so what does this have to do with your problem? You're using:

imageBounds = [[-90, -180], [90, 180]];

But, since Leaflet will clamp latitudes, that's actually the same as doing:

imageBounds = [[-85.01, -180], [85.01, 180]];

Keep this in mind when using L.ImageOverlays that cover areas near the poles. You probably want to recreate your image using a narrower band of latitudes.