`xy_bbox` does not consider `cornerOfOrigin`

[claxn]

When requesting the xy_bbox property from a TileMatrixSet instance with cornerOfOrigin="bottomLeft", top and bottom of the bounding box are flipped. There is probably a bug in xy_bbox, since it does not consider the cornerOfOrigin. The following lines need to consider the right tile indices, depending on cornerOfOrigin:

https://github.com/developmentseed/morecantile/blob/main/morecantile/models.py#L1262-L1266

Here is a MWE with a walkthrough of the issues:

from morecantile.models import TileMatrixSet, Tile
import pyproj

extent = [-100_000, -100_000, 200_000, 200_000]
tms = TileMatrixSet.custom(
            extent,
            pyproj.CRS.from_epsg(3857),
            minzoom=0,
            maxzoom=1,
            corner_of_origin="bottomLeft",
        )

The expected bounding box is BoundingBox(left=-100000.0, bottom=-100000.0, right=200000.0, top=200000.0), but the result is flipped in y:

tms.xy_bbox

BoundingBox(left=-100000.0, bottom=200000.0, right=200000.0, top=-100000.0)

This is due to two reasons. First, tms._lr and tms._ul return the wrong coordinates for y:

tms._ul(Tile(0, 0, 0)).y, tms._lr(Tile(0, 0, 0)).y 

(-100000.0, 200000.0)

xy_bounds of a tile is correct:

tms.xy_bounds(Tile(0, 0, 0))

BoundingBox(left=-100000.0, bottom=-100000.0, right=200000.0, top=200000.0)

The first issue is because there is a wrong index in the coordinate computation:

https://github.com/developmentseed/morecantile/blob/main/morecantile/models.py#L1123

https://github.com/developmentseed/morecantile/blob/main/morecantile/models.py#L1158

This should be the same as in xy_bounds, which means:

origin_y + (t.y + 1) * matrix.cellSize * matrix.tileHeight in tms._ul and origin_y + t.y * matrix.cellSize * matrix.tileHeight in tms._lr.

The second issue is, that tms.xy_bbox uses the wrong tile to compute the bounding box of the tms:

https://github.com/developmentseed/morecantile/blob/main/morecantile/models.py#L1262-L1266

This needs to be adjusted to:

if matrix.cornerOfOrigin == "topLeft":
    left, top = self._ul(Tile(0, 0, zoom))
    right, bottom = self._lr(Tile(matrix.matrixWidth - 1, matrix.matrixHeight - 1, zoom))
else:
    left, top = self._ul(Tile(0, matrix.matrixHeight - 1, zoom))
    right, bottom = self._lr(Tile(matrix.matrixWidth - 1, 0, zoom))

I hope I am not misunderstanding sth. here - please let me know if you require further inputs from my side. Maybe it would be also a good idea to cross-compare bounds in new tests, e.g.: tms._lr(Tile(0, 0, 0)).y == tms.xy_bounds(Tile(0, 0, 0)).bottom

Thank you in advance!

[vincentsarago]

@claxn please provide a MWE 🙏

xy_box use _lr and _ul method which take the origin in account 🤷

morecantile/morecantile/models.py

Lines 1120 to 1124 in 71f1ee1

	y_coord = (
	origin_y - t.y * matrix.cellSize * matrix.tileHeight
	if matrix.cornerOfOrigin == "topLeft"
	else origin_y + t.y * matrix.cellSize * matrix.tileHeight
	)

https://github.com/developmentseed/morecantile/blob/71f1ee18dec9857fcb518721b2f8ca14453055c2/morecantile/models.py#L1155C9-L1159

[claxn]

@vincentsarago I updated the issue 🙂

[vincentsarago]

@claxn thank @claxn 🙏

I don't have bandwidth right now so if you could start a PR that would be lovely 🙏