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add z_index function #24

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add z_index function #24

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9f812d0
add z_index function
rafaqz Jan 22, 2023
074d559
Update src/tiles.jl
rafaqz Jan 22, 2023
8c5e037
Merge branch 'master' into z_index
asinghvi17 Sep 26, 2024
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23 changes: 23 additions & 0 deletions src/tiles.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,26 @@ function Tile(point, zoom::Integer, crs::WGS84)
return Tile(xtile, ytile, zoom)
end

"""
z_index(extent::Extent, res::NamedTuple, crs::WebMercator) => Int

Calculate a z value from `extent` and pixel resolution `res` for `crs`.
The rounded mean calculated z-index for X and Y resolutions is returned.

`res` should be `(X=xres, Y=yres)` to match the extent.

We assume tiles are the standard 256*256 pixels. Note that this is not an
enforced standard, and that retina tiles are 512*512.
Comment on lines +121 to +122
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Perhaps it's best to directly add the tile size as an argument?

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Ok I considered that too. I guess a keyword with default is best.

"""
function z_index(extent::Extent, res::NamedTuple, crs::WebMercator)
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Should this also accept tuples (x, y) as Makie does? In that case we can also make z_index(..., Tuple) = z_index(..., (; X = ..., Y = ...)) or so.

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There should probably also be a catchall method to error when crs is not WebMercator (for now...)

ntiles = map(r -> r / 256, res)
tile_size_X = (extent.X[2] - extent.X[1]) / ntiles.X
tile_size_Y = (extent.Y[2] - extent.Y[1]) / ntiles.Y
tile_size = (tile_size_X + tile_size_Y) / 2
z = log2(CE / tile_size)
return round(Int, z)
end

struct TileGrid
grid::CartesianIndices{2, Tuple{UnitRange{Int}, UnitRange{Int}}}
z::Int
Expand Down Expand Up @@ -140,6 +160,7 @@ end

Base.length(tilegrid::TileGrid) = length(tilegrid.grid)
Base.size(tilegrid::TileGrid, dims...) = size(tilegrid.grid, dims...)
Base.axes(tilegrid::TileGrid, dims...) = axes(tilegrid.grid, dims...)
Base.getindex(tilegrid::TileGrid, i) = Tile(tilegrid.grid[i], tilegrid.z)
Base.firstindex(tilegrid::TileGrid) = firstindex(tilegrid.grid)
Base.lastindex(tilegrid::TileGrid) = lastindex(tilegrid.grid)
Expand Down Expand Up @@ -216,3 +237,5 @@ function GeoInterface.extent(tilegrid::TileGrid, crs::WebMercator)

return Extent(X=(left, right), Y=(bottom, top))
end