Created
April 27, 2020 13:35
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_ogc_crs84 = 'urn:ogc:def:crs:OGC:1.3:CRS84' | |
_web_mercator_epsg = 'EPSG:3857' | |
def _meters_per_pixel(zoom: int, lat: float=0.0, tile_size:int=256) -> float: | |
""" | |
Return the pixel resolution for a given mercator tile zoom and lattitude. | |
:param zoom: Mercator zoom level | |
:param lat: Latitude in decimal degree. Optional (default: 0) | |
:param tile_size: Mercator tile size (default: 256). | |
:type tile_size: int, optional | |
:return: Pixel resolution in meters | |
:rtype: float | |
""" | |
return (math.cos(lat * math.pi / 180.0) * 2 * math.pi * 6378137) / ( | |
tile_size * 2 ** zoom | |
) | |
def zoom_for_pixelsize(pixel_size, max_z=24, tile_size=256, lat=0) -> int: | |
""" | |
Get mercator zoom level corresponding to a pixel resolution. | |
Freely adapted from | |
https://github.com/OSGeo/gdal/blob/b0dfc591929ebdbccd8a0557510c5efdb893b852/gdal/swig/python/scripts/gdal2tiles.py#L294 | |
:param pixel_size: Pixel size in meters | |
:param max_z: Max mercator zoom level allowed. Optional (default: 24) | |
:param tile_size: Mercator tile size. Optional (default: 256). | |
:param lat: Latitude of pixel size. Optional (default: 0) | |
:return: Mercator zoom level corresponding to the pixel resolution | |
""" | |
for z in range(max_z): | |
if pixel_size > _meters_per_pixel(z, lat, tile_size=tile_size): | |
return max(0, z - 1) # We don't want to scale up | |
return max_z - 1 | |
def zoom_for_poly_wgs84(poly_wgs84: Polygon, map_size: int = 900) -> int: | |
""" | |
Computes the **approximate** zoom value needed to cover the given polygon in a web map. | |
Parameters | |
:param poly_wgs84: Polygon in wgs84 | |
:param map_size: approx map widget size in pixels. optional | |
:return: zoom to use to show polgyon | |
""" | |
wm_poly = reproject(poly_wgs84, _ogc_crs84, _web_mercator_epsg) | |
(xmin, ymin, xmax, ymax) = wm_poly.bounds | |
width_m = xmax - xmin | |
pixel_size = width_m / map_size | |
return zoom_for_pixelsize(pixel_size, lat=poly_wgs84.centroid.y) |
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