186 lines
5.3 KiB
Python
186 lines
5.3 KiB
Python
"""Coordinate reference systems and functions
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PROJ is the law of this land: https://proj.org/. But whereas PROJ
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coordinate reference systems are described by strings of parameters such as
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+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs
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here we use mappings:
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{'proj': 'longlat', 'ellps': 'WGS84', 'datum': 'WGS84', 'no_defs': True}
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"""
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from six import string_types
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def to_string(crs):
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"""Turn a parameter mapping into a more conventional PROJ.4 string.
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Mapping keys are tested against the ``all_proj_keys`` list. Values of
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``True`` are omitted, leaving the key bare: {'no_defs': True} -> "+no_defs"
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and items where the value is otherwise not a str, int, or float are
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omitted.
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"""
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items = []
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for k, v in sorted(filter(
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lambda x: x[0] in all_proj_keys and x[1] is not False and (
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isinstance(x[1], (bool, int, float)) or
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isinstance(x[1], string_types)),
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crs.items())):
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items.append(
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"+" + "=".join(
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map(str, filter(
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lambda y: (y or y == 0) and y is not True, (k, v)))))
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return " ".join(items)
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def from_string(prjs):
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"""Turn a PROJ.4 string into a mapping of parameters.
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Bare parameters like "+no_defs" are given a value of ``True``. All keys
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are checked against the ``all_proj_keys`` list.
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"""
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parts = [o.lstrip('+') for o in prjs.strip().split()]
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def parse(v):
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try:
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return int(v)
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except ValueError:
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pass
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try:
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return float(v)
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except ValueError:
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return v
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items = map(
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lambda kv: len(kv) == 2 and (kv[0], parse(kv[1])) or (kv[0], True),
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(p.split('=') for p in parts))
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return dict((k, v) for k, v in items if k in all_proj_keys)
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def from_epsg(code):
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"""Given an integer code, returns an EPSG-like mapping.
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Note: the input code is not validated against an EPSG database.
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"""
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if int(code) <= 0:
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raise ValueError("EPSG codes are positive integers")
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return {'init': "epsg:%s" % code, 'no_defs': True}
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# Below is the big list of PROJ4 parameters from
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# http://trac.osgeo.org/proj/wiki/GenParms.
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# It is parsed into a list of parameter keys ``all_proj_keys``.
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_param_data = """
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+a Semimajor radius of the ellipsoid axis
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+alpha ? Used with Oblique Mercator and possibly a few others
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+axis Axis orientation (new in 4.8.0)
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+b Semiminor radius of the ellipsoid axis
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+datum Datum name (see `proj -ld`)
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+ellps Ellipsoid name (see `proj -le`)
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+init Initialize from a named CRS
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+k Scaling factor (old name)
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+k_0 Scaling factor (new name)
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+lat_0 Latitude of origin
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+lat_1 Latitude of first standard parallel
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+lat_2 Latitude of second standard parallel
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+lat_ts Latitude of true scale
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+lon_0 Central meridian
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+lonc ? Longitude used with Oblique Mercator and possibly a few others
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+lon_wrap Center longitude to use for wrapping (see below)
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+nadgrids Filename of NTv2 grid file to use for datum transforms (see below)
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+no_defs Don't use the /usr/share/proj/proj_def.dat defaults file
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+over Allow longitude output outside -180 to 180 range, disables wrapping (see below)
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+pm Alternate prime meridian (typically a city name, see below)
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+proj Projection name (see `proj -l`)
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+south Denotes southern hemisphere UTM zone
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+to_meter Multiplier to convert map units to 1.0m
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+towgs84 3 or 7 term datum transform parameters (see below)
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+units meters, US survey feet, etc.
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+vto_meter vertical conversion to meters.
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+vunits vertical units.
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+x_0 False easting
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+y_0 False northing
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+zone UTM zone
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+a Semimajor radius of the ellipsoid axis
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+alpha ? Used with Oblique Mercator and possibly a few others
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+azi
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+b Semiminor radius of the ellipsoid axis
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+belgium
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+beta
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+czech
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+e Eccentricity of the ellipsoid = sqrt(1 - b^2/a^2) = sqrt( f*(2-f) )
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+ellps Ellipsoid name (see `proj -le`)
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+es Eccentricity of the ellipsoid squared
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+f Flattening of the ellipsoid (often presented as an inverse, e.g. 1/298)
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+gamma
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+geoc
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+guam
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+h
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+k Scaling factor (old name)
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+K
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+k_0 Scaling factor (new name)
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+lat_0 Latitude of origin
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+lat_1 Latitude of first standard parallel
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+lat_2 Latitude of second standard parallel
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+lat_b
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+lat_t
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+lat_ts Latitude of true scale
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+lon_0 Central meridian
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+lon_1
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+lon_2
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+lonc ? Longitude used with Oblique Mercator and possibly a few others
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+lsat
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+m
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+M
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+n
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+no_cut
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+no_off
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+no_rot
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+ns
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+o_alpha
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+o_lat_1
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+o_lat_2
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+o_lat_c
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+o_lat_p
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+o_lon_1
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+o_lon_2
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+o_lon_c
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+o_lon_p
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+o_proj
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+over
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+p
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+path
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+proj Projection name (see `proj -l`)
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+q
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+R
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+R_a
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+R_A Compute radius such that the area of the sphere is the same as the area of the ellipsoid
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+rf Reciprocal of the ellipsoid flattening term (e.g. 298)
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+R_g
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+R_h
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+R_lat_a
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+R_lat_g
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+rot
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+R_V
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+s
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+south Denotes southern hemisphere UTM zone
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+sym
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+t
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+theta
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+tilt
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+to_meter Multiplier to convert map units to 1.0m
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+units meters, US survey feet, etc.
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+vopt
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+W
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+westo
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+x_0 False easting
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+y_0 False northing
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+zone UTM zone
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+wktext Marker
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"""
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_lines = filter(lambda x: len(x) > 1, _param_data.split("\n"))
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all_proj_keys = list(
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set(line.split()[0].lstrip("+").strip() for line in _lines)) + ['no_mayo']
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