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[main] Fix quadtree leaf boundaries to match cuSpatial's clamped scale #87

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[main] Fix quadtree leaf boundaries to match cuSpatial's clamped scale #87

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24 changes: 17 additions & 7 deletions src/segger/geometry/quadtree.py
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,10 @@ def get_quadtree_kwargs(
max_depth = 1
while extent // (1 << max_depth) > 0:
max_depth += 1
scale = extent // (1 << max_depth - 1)
max_depth = min(max_depth, 15)

# Match cuSpatial's own min-scale formula so it never silently clamps this up.
scale = extent / ((1 << max_depth) + 2)

# Return as dictionary
return dict(
Expand All @@ -49,7 +52,7 @@ def get_quadtree_kwargs(
y_min=y_min,
y_max=y_max,
scale=scale,
max_depth=min(max_depth, 15),
max_depth=max_depth,
)


Expand Down Expand Up @@ -100,6 +103,8 @@ def get_quadrant_bounds(
x_max: float,
y_min: float,
y_max: float,
scale: float,
max_depth: int,
):
"""
Add spatial bounds to each leaf in a cuSpatial quadtree.
Expand All @@ -115,20 +120,23 @@ def get_quadrant_bounds(
Full extent of the quadtree in x-direction.
y_min, y_max : float
Full extent of the quadtree in y-direction.
scale : float
The `scale` actually used by cuSpatial to build `quadtree` (i.e. the
leaf cell width). Must match, or leaf boundaries will be computed for
a different cell size than the tree cuSpatial built.
max_depth : int
The `max_depth` actually used by cuSpatial to build `quadtree`.

Returns
-------
cudf.DataFrame
Input DataFrame with added bounding box columns: 'x_min', 'x_max',
'y_min', and 'y_max'.
"""
width = x_max - x_min
height = y_max - y_min
levels = quadtree['level'].astype(float) + 1
coords = cp.array(keys_to_coordinates(quadtree['key'].to_numpy()))
quadrant_max = np.ceil(np.log2(max(width, height)))
quadrant_dim = 2 ** (quadrant_max - levels)

quadrant_dim = scale * 2 ** (max_depth - levels)

quadtree['x_min'] = x_min + coords[0] * quadrant_dim
quadtree['x_max'] = quadtree['x_min'] + quadrant_dim
quadtree['y_min'] = y_min + coords[1] * quadrant_dim
Expand Down Expand Up @@ -215,6 +223,8 @@ def get_quadtree_index(
x_max=x_max,
y_min=y_min,
y_max=y_max,
scale=scale,
max_depth=max_depth,
)

return indices, quadtree, kwargs
Expand Down