Jens
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86 lines
2.8 KiB
Python
86 lines
2.8 KiB
Python
"""Choosing which raster cells a drawn selection covers.
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``rasterio.features.geometry_mask`` selects a cell when the cell *centre* falls
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inside the geometry. That is the right rule for a selection spanning many
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cells, and the wrong one for a small selection: a rectangle smaller than a cell,
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or one landing between four centres, selects nothing. The analysis then reports
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zeros, which on screen reads as "we measured this area and found nothing"
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rather than "this selection is finer than the source raster".
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Falling back to every touched cell keeps a small selection answerable, at the
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cost of analysing more ground than was drawn. That trade is only honest if it
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is stated, so the fallback is reported alongside the result.
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"""
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from __future__ import annotations
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from dataclasses import dataclass
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from typing import Any
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@dataclass(frozen=True)
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class RasterCellSelection:
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mask: Any
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mode: str
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expanded_to_touched_cells: bool
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warning: str | None
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def select_cells(
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geometry,
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*,
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out_shape: tuple[int, int],
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transform,
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cell_area_m2: float | None = None,
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) -> RasterCellSelection:
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"""Mask the cells a selection covers, widening only when it covers none.
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``geometry`` must already be in the raster's own CRS.
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"""
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from rasterio.features import geometry_mask
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from shapely.geometry import mapping
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shapes = [mapping(geometry)]
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mask = geometry_mask(shapes, out_shape=out_shape, transform=transform, invert=True)
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if mask.any():
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return RasterCellSelection(
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mask=mask,
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mode="cell_centre",
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expanded_to_touched_cells=False,
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warning=None,
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)
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touched = geometry_mask(
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shapes,
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out_shape=out_shape,
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transform=transform,
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invert=True,
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all_touched=True,
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)
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if not touched.any():
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# The selection does not reach the raster at all. Widening the rule
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# must never manufacture coverage that is genuinely absent.
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return RasterCellSelection(
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mask=mask,
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mode="cell_centre",
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expanded_to_touched_cells=False,
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warning=None,
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)
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cell_count = int(touched.sum())
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if cell_area_m2:
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analysed_ha = cell_count * float(cell_area_m2) / 10_000.0
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detail = f"{cell_count} rastercel{'' if cell_count == 1 else 'len'} ({analysed_ha:.1f} ha)"
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else:
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detail = f"{cell_count} rastercel{'' if cell_count == 1 else 'len'}"
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return RasterCellSelection(
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mask=touched,
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mode="all_touched",
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expanded_to_touched_cells=True,
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warning=(
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f"De selectie is kleiner dan één rastercel van deze bron. Het resultaat geldt voor {detail} "
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"die de selectie raken, dus voor een groter gebied dan getekend."
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),
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)
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