`Tile.CenterLat` is inherently confusing

[RamType0]

NetTopologySuite.IO.VectorTiles/src/NetTopologySuite.IO.VectorTiles/Tiles/Tile.cs

Line 62 in 5ac51b3

this.CenterLat = (double)((this.Top + this.Bottom) / 2.0);

Since Web Mercator does not map latitude linear, Center latitude does not represent center of the rendered map.

[FObermaier]

What do we use it for? The only reference it is used in this library is here:

NetTopologySuite.IO.VectorTiles/src/NetTopologySuite.IO.VectorTiles/Tiles/Tile.cs

Lines 384 to 411 in 16c930f

	public ulong GetSubTileIdFor(double lat, double lon)
	{
	const int factor = 2;
	int zoom = this.Zoom + 1;
	int x = 0, y = 0;
	if (lat >= this.CenterLat && lon < this.CenterLon)
	{
	x = this.X * factor;
	y = this.Y * factor;
	}
	else if (lat >= this.CenterLat && lon >= this.CenterLon)
	{
	x = this.X * factor + factor - 1;
	y = this.Y * factor;
	}
	else if (lat < this.CenterLat && lon < this.CenterLon)
	{
	x = this.X * factor;
	y = this.Y * factor + factor - 1;
	}
	else if (lat < this.CenterLat && lon >= this.CenterLon)
	{
	x = this.X * factor + factor - 1;
	y = this.Y * factor + factor - 1;
	}
	return Tile.CalculateTileId(zoom, x, y);
	}

The computation and usage of Tile.CenterLat in GetSubTileIdFor is correct as far as I can tell. The only thing I see we can do about this is clarify this in the code documentation.

[RamType0]

The computation and usage of Tile.CenterLat in GetSubTileIdFor is correct as far as I can tell.

No, it is incorrect usage.

We need the center in Web Mercator coordinate for this operation.
But you are using Longitude-Latitude coordinate center for the operation.

Try execute this code.

Tile tile001 = new(0, 0, 1);
Tile tile002 = new(0, 0, 2);

Console.WriteLine($"Tile001 center lat: {tile001.CenterLat}");
Console.WriteLine($"Tile002 bottom: {tile002.Bottom}");
Console.WriteLine($"Tile001 center lon: {tile001.CenterLon}");
Console.WriteLine($"Tile002 right: {tile002.Right}");

If the computation and usage of Tile.CenterLat in GetSubTileIdFor is correct,"Tile001 center lat" and "Tile002 bottom" are same.

But actually, it shows following result.

Tile001 center lat: 42.5255643899033
Tile002 bottom: 66.51326044311186
Tile001 center lon: -90
Tile002 right: -90

Thus, Tile.CenterLat is too much confusing as you also used it incorrectly.

BTW, I think ulong GetSubTileIdFor(double lat, double lon) is a bad API.
It returns incorrect result for lat and lon outside of the tile.
What we need is ulong GetTileIdFor(int zoom, double latitude, double longitude).