Allow custom pixel selection method

[vincentsarago]

This is how it could look like.

The idea is to build a MosaicMethod class with 3 required method:

• feed: add tile data and mask
• is_done: check if we are done processing
• get_data: return tile and mask data

class FirstMethod():

    def __init__(self, tile=None):
        self.tile = tile
        self.exit_when_filled = True

    def get_data(self):
        """Return tile data and mask."""
        if self.tile is not None:
            return self.tile.data, ~self.tile.mask[0] * 255
        else:
            return None, None

    def is_done(self):
        """Check if we need more data."""
        if self.exit_when_filled and not numpy.ma.is_masked(self.tile):
            return True

    def feed(self, tile):
        """Add data to tile."""
        if self.tile is None:
            self.tile = tile

        pidex = self.tile.mask & ~tile.mask

        mask = numpy.where(pidex, tile.mask, self.tile.mask)
        self.tile = numpy.ma.where(pidex, tile, self.tile)
        self.tile.mask = mask

Implementation:

    algo = FirstMethod()

    _tiler = partial(tiler, tile_x=tile_x, tile_y=tile_y, tile_z=tile_z, **kwargs)
    max_threads = int(os.environ.get("MAX_THREADS", multiprocessing.cpu_count() * 5))

    for chunks in _chunks(assets, max_threads):
        with futures.ThreadPoolExecutor(max_workers=max_threads) as executor:
            future_tasks = [executor.submit(_tiler, asset) for asset in chunks]

        for t, m in _filter_futures(future_tasks):
            t = numpy.ma.array(t)
            t.mask = m == 0

            algo.feed(t)
            if algo.is_done():
                return algo.get_data()