Leaflet calculate map origin left top point

Question

The short question

Given:

• map center (in lat long)
• map boundaries (in lat long)
• position of the point A on the layout relative to the layout origin

How to compute: position of the point A in lat/long (not using map object only CRS)

Or simpler

Given:

• map center (in lat long)
• map boundaries (in lat long)

How to compute: position of the layout origin in pixels (not using map object only CRS)

If I had response for the second one I could figure out response for the first one.

---

Longer explanation

The whole task here is given: 1. map center (lat long) 2. map bounds (lat long) 3. point (px relative origin pixel) calculate point position (3) in lat long.

Consider zoom always constant here = 18

Why: I had map UX with properties : center and bounds all in lat long, then I have svg layout as a layer on lefalet map (SVGOverlay) , when I add some object on this svg layout it's position will be given relative to this layout origin, I want to display it as lat long.

I can use map.layerPointToLatLng to get exactly required result, but for this I had to have reference to already created leaflet map, but in some scenarios I don't have one, for example I store in db 3 parameters which describes the map and objects on it : map center, map bounds and svg object point relative to the layout origin and want to calculate lat long of the object without creating map instance.

So I was digging into leaflet library layerPointToLatLng implementation and flow from there:

• getPixelOrigin
• _getNewPixelOrigin
• getSize <-- Probably issue is here
• Given size, center & size calculate origin and then its straightforward unproject(origin + relative point position)

getSize here is just

                this._container.clientWidth || 0,
                this._container.clientHeight || 0);

So it was set up by image overlay, like this

    _reset: function () {
        var image = this._image,
            bounds = new Bounds(
                this._map.latLngToLayerPoint(this._bounds.getNorthWest()),
                this._map.latLngToLayerPoint(this._bounds.getSouthEast())),
            size = bounds.getSize();

        DomUtil.setPosition(image, bounds.min);

        image.style.width  = size.x + 'px';
        image.style.height = size.y + 'px';
    },

So I've tried replicate all this flow but with this _container ref like this

export interface MapEnv {
    zoom: number;
    crs: L.CRS;
}

export const defaultMapEnv: MapEnv = {
    zoom: 18,
    crs: CRS.EPSG3857
};

export const getMapOrigin = (
    bounds: LatLngBounds,
    center: Point,
    { crs, zoom } = defaultMapEnv
): Point => {
    //
    const lbounds = new L.LatLngBounds(bounds.southWest, bounds.northEast);
    const lcenter = new L.LatLng(center.x, center.y);

    const bounds1 = new L.Bounds(
        crs.latLngToPoint(lbounds.getNorthWest(), zoom),
        crs.latLngToPoint(lbounds.getSouthEast(), zoom)
    );

    const size = bounds1.getSize();

    const ppp = crs.latLngToPoint(lcenter, zoom);

    const orig = ppp
        .subtract(size.divideBy(2))
        .round();

    return { x: orig.x, y: orig.y };
};

export const mapPoint2LatLong = (
    orig: Point,
    point: Point,
    { crs, zoom } = defaultMapEnv
) => {

    const lorig = new L.Point(orig.x, orig.y);
    const lpoint = new L.Point(point.x, point.y);

    const res = crs.pointToLatLng(lorig.add(lpoint), zoom);

    return { x: res.lat, y: res.lng };
};

But this implementation always gives some small offset relative to the correct lat long coordinates Example:

            const pt = [57320, 43710];

            console.log('center', mapProps.center);
            console.log('bounds', mapProps.bounds);
            console.log(
                'map latlong',
                map.layerPointToLatLng(new L.Point(pt[0], pt[1]))
            );
            const orig = getMapOrigin(mapProps.bounds, mapProps.center);
            const ll = mapPoint2LatLong(orig, { x: pt[0], y: pt[1] });
            console.log('custom latlong', ll);


=====
center {x: 55.159897, y: 61.402554}
bounds 
{
northEast: (2) [55.293583, 61.804276]
southWest: (2) [55.018969, 61.094971]
}
map latlong {lat: 55.02665382398748, lng: 61.708027124404914} <-- Correct
custom latlong {x: 55.16323630220735, y: 61.35539174079896} <-- Incorrect (small offset always)

Some hints, suggestions how to correct this ?