atlas: remove usage of tegola.Tile

[ear7h]

note: this pr had a different name because I originally wrote this as part of the changes in 46e9eeb

This pr has two major changes to remove the tegola.Tile from the encode function. The first is related to clipping and the second to the epsilon value. I've written the explicit changes below bc they can be hard to follow.

This pr also has new tests for Encode that test the clipping mechanism. This required a change in the test provider to be able to specify the features it contains.

clipping

tegola/tile.go

Lines 101 to 104 in 46e9eeb

	t.bufpext = &geom.Extent{
	0 - t.Buffer, 0 - t.Buffer,
	t.Extent + t.Buffer, t.Extent + t.Buffer,
	}

tegola/tile.go

Lines 192 to 194 in 46e9eeb

	func (t *Tile) PixelBufferedBounds() (bounds [4]float64, err error) {
	return t.bufpext.Extent(), nil
	}

tegola/atlas/map.go

Lines 208 to 213 in 46e9eeb

	pbb, err := tegolaTile.PixelBufferedBounds()
	if err != nil {
	return fmt.Errorf("err calculating tile pixel buffer bounds: %v", err)
	}
	clipRegion = geom.NewExtent([2]float64{pbb[0], pbb[1]}, [2]float64{pbb[2], pbb[3]})

and the new:

tegola/atlas/map.go

Lines 208 to 211 in 428bd2c

	clipRegion = (&geom.Extent{
	0, 0,
	float64(m.TileExtent), float64(m.TileExtent),
	}).ExpandBy(float64(m.TileBuffer))

epsilon

Current:

tegola/tile.go

Lines 209 to 225 in 46e9eeb

	// This is from Leafty
	func (t *Tile) ZEpislon() float64 {
	if t.Z == MaxZ {
	return 0
	}
	epi := t.Tolerance
	if epi <= 0 {
	return 0
	}
	ext := t.Extent
	denom := (math.Exp2(float64(t.Z)) * ext)
	e := epi / denom
	return e
	}

New:

tegola/maths/simplify/epislon.go

Lines 13 to 28 in 428bd2c

	// This is from Leafty
	func ZEpislon(z uint, tileExtent float64) float64 {
	if z == tegola.MaxZ {
	return 0
	}
	epi := DefaultTolerence
	if epi <= 0 {
	return 0
	}
	denom := (math.Exp2(float64(z)) * tileExtent)
	e := epi / denom
	return e
	}

[coveralls]

Pull Request Test Coverage Report for Build 1795

• 8 of 22 (36.36%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.9%) to 44.626%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cmd/tegola/cmd/cache/worker.go	0	2	0.0%
atlas/map.go	8	11	72.73%
atlas/atlas.go	0	9	0.0%

Files with Coverage Reduction	New Missed Lines	%
atlas/atlas.go	1	5.06%
atlas/map.go	1	62.75%

Totals
Change from base Build 1787:	-0.9%
Covered Lines:	24740
Relevant Lines:	55439

---

💛 - Coveralls

[ear7h]

Since it wasn't much, I also removed the last use of tegola.Tile from the atlas package and added it to this PR. However, I ran into some inconsistency between SeedMapTile and PurgeMapTile, I think they should both use a tile or both use a zxy.

tegola/atlas/atlas.go

Line 105 in d5f77ab

func (a *Atlas) SeedMapTile(ctx context.Context, m Map, z, x, y uint) error {

tegola/atlas/atlas.go

Line 138 in d5f77ab

func (a *Atlas) PurgeMapTile(m Map, tile *slippy.Tile) error {

I'm leaning towards the tile...

[ARolek]

@ear7h let's use the tile for SeedMapTile.

[ARolek]

This looks really good, thanks for tackling it. I have a few comments inline. Also, if tegola tile is no longer being used, is there any reason to not purge it with the commit?

[ARolek]

@ear7h this looks great. Please clean up the commit history and then I will rebase it into v0.11.x

[ear7h]

I had to rebase, but I was running into merge issues and simply applied the commit 3ff9ac6 to v0.11.x. GH automatically closed this because I accidentally pushed freshly created branch without applying the commit.

[ARolek]

just remove encode-cleanup.patch from the commit and then we're good.