small error in tms bounds calculation

[dcherian]

The right for bounds should be exactly 180; and IIUC left and right for xy_bounds should have the same absolute value and opposite sign.

import morecantile

tms = morecantile.tms.get("WebMercatorQuad")
tile = morecantile.Tile(x=0,y=0,z=0)
print(tms.bounds(tile))
# BoundingBox(left=-180.0, bottom=-85.0511287798066, right=180.00000000000009, top=85.0511287798066)
print(tms.xy_bounds(tile))
# BoundingBox(left=-20037508.342789244, bottom=-20037508.34278925, right=20037508.34278925, top=20037508.342789244)

[vincentsarago]

this is clearly a precision issue coming from

morecantile/morecantile/models.py

Lines 1112 to 1118 in 9600968

	left = origin_x + math.floor(t.x / cf) * matrix.cellSize * cf * matrix.tileWidth
	top = origin_y - t.y * matrix.cellSize * matrix.tileHeight
	right = (
	origin_x
	+ (math.floor(t.x / cf) + 1) * matrix.cellSize * cf * matrix.tileWidth
	)
	bottom = origin_y - (t.y + 1) * matrix.cellSize * matrix.tileHeight

we get bottom=-20037508.34278925 and right=20037508.34278925 while it should be .342789244 for both values 😭

[vincentsarago]

to be simple, when we calculate to coordinates for the tile's corners we do origin + pixelSize * nPixel, for tile 0-0-0 this result in :

x_origin = -20037508.342789244
pixel_size = 156543.033928041  # from TMS document
n_pixel = 256  # from TMS document 

pixel_size * n_pixel
>> 40075016.685578495

origin + pixelSize * nPixel
>> 20037508.34278925

This is a big issue for morecantile because we do calculation based on number from a JSON document (TMS) while mercantile or utile use equations.