I’m trying to setup a custom CRS in flutter_map to cover a small area with a different coordinate system. I’ve setup a proj4 CRS as below:

final epsg27700 = proj4.Projection.get('EPSG:27700') ?? proj4.Projection.add('EPSG:27700', '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894 +units=m +no_defs');

final resolutions = zoomLevels.map<double>((level) => level.resolution).toList();

final crs = Proj4Crs.fromFactory(
  code: 'EPSG:27700',
  proj4Projection: epsg27700,
  resolutions: resolutions,
  bounds: bounds,
  origins: [
    Point(
      bounds.topLeft.x,
      bounds.bottomRight.y,
    )
  ],
);

Then loaded into the map:

    FlutterMap(
          mapController: widget.mapController.mapController,
          options: MapOptions(
            crs: _projection,
            initialCenter: _tileProvider.mapCenter,
            minZoom: 0,
            maxZoom: 2,
          ),
          children: [
            TileLayer(
              zoomReverse: true,
              tileProvider: _tileProvider,
              tileBounds: _tileBounds,
            )
          ],
        ),

This works correctly on first load but when I try to zoom in or out, I get the following:

Invalid value: Not in inclusive range 0..2: 3)

It seems to be that it’s trying to load resolutions outside of the ones specified. There are only 3 resolutions specified for the 3 different levels in the map file. As you can see I have specified the maxZoom at 2 but it’s attempting to find a resolution at index 3.

There’s no clear documentation on how the resolutions relate to min/maxZoom or min/maxNativeZoom or the available tile levels that I can find so I may be doing something incorrectly here.