Transforming point from EPSG:3844 to EPSG:3857 with proj4js

Question

I'm having an issue transforming a point from EPSG:3844 to EPSG:3857 using Proj4JS. The transformation it performs seems off compared to the result given by PostGIS, pyproj, rgeo-proj4 or even epsg.io.

PostGIS sample:

select st_astext(st_transform(st_geomfromtext('point(432142.945 474552.670)', 3844), 3857));

This is the code in question (JSFiddle):

proj4.defs([
  [
    'EPSG:3844',
    '+proj=sterea +lat_0=46 +lon_0=25 +k=0.99975 +x_0=500000 +y_0=500000 +ellps=krass +towgs84=2.329,-147.042,-92.08,0.309,-0.325,-0.497,5.69 +units=m +no_defs +type=crs',
  ],
  [
    'EPSG:3857',
    '+proj=merc +a=6378137 +b=6378137 +lat_ts=0 +lon_0=0 +x_0=0 +y_0=0 +k=1 +units=m +nadgrids=@null +wktext +no_defs +type=crs',
  ],
]);
const actual = proj4('EPSG:3844', 'EPSG:3857', [432142.945, 474552.67]);
const expected = [2685681.568887065, 5743146.959786006];
console.log('Actual:', actual);
console.log('Expected:', expected);

<script src="https://cdnjs.cloudflare.com/ajax/libs/proj4js/2.8.0/proj4.js"></script>

I suspect it has something to do with the Helmert transformation parameters given in +towgs84=2.329,-147.042,-92.08,0.309,-0.325,-0.497,5.69? If so, what are the correct parameters?

Answer 1

You are right regarding wrong towgs84 parameters. If you take the ones from https://spatialreference.org/ref/epsg/3844/html/:

TOWGS84[33.4,-146.6,-76.3,-0.359,-0.053,0.844,-0.17326243724756094]

you'll get much better result: [2685681.014671648, 5743147.970431625]. It's still not exactly what you expect, but at least you know where the discrepancy comes from.