38U 37U boundaries issue

[senyai]

Hi! I have this polygon:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
        [42.0175123214722,52.3537568545561],
        [41.9911193847656,52.3522365310418],
        [42.0013117790222,52.352714914338],
        [42.0175123214722,52.3537568545561]
          ]
        ]
      }
    }
  ]
}

It looks all right on https://geojson.io, but when I use from_latlon the coordinates aren't looking good:

for lon, lat in (
        [42.0175123214722,52.3537568545561],
        [41.9911193847656,52.3522365310418],
        [42.0013117790222,52.352714914338],
        [42.0175123214722,52.3537568545561],
    ):
    res = utm.from_latlon(lat, lon)
    print(res)

(296891.7091715876, 5804572.595912797, 38, 'U') (703702.9711657077, 5804427.828889267, 37, 'U') (295783.8970581499, 5804502.368612623, 38, 'U') (296891.7091715876, 5804572.595912797, 38, 'U')

Is this expected behavior?

[bartvanandel]

Yes, this is expected behavior. If you provide the points individually, the algorithm will determine the zone for each point individually. You can actually see this in the results you've pasted, which contain zone numbers 38 and 37.

To have the results all in the same zone, you can either force the zone, or provide the latitudes and longitudes as lists. In the latter case, the first point will determine the zone, and all other points will be put into that zone as well.

This will currently only work if all points are on the same side of the equator, but there are some requests to change or work around this.

[senyai]

Thank you for your explanation.