Merge pull request #3 from geopython/encode-v32

Encoding for GML v3.2 and GeoRSS

Author: constantinius

README.md

@@ -1,6 +1,6 @@
 # pygml
 
-A pure python parser for OGC GML Geometries.
+A pure python parser and encoder for OGC GML Geometries.
 
 [![PyPI version](https://badge.fury.io/py/pygml.svg)](https://badge.fury.io/py/pygml)
 [![CI](https://github.com/geopython/pygml/actions/workflows/test.yaml/badge.svg)](https://github.com/geopython/pygml/actions/workflows/test.yaml)
@@ -29,3 +29,18 @@ Geometry(geometry={'type': 'Point', 'coordinates': (1.0, 1.0)})
 >>> print(geom.__geo_interface__)
 {'type': 'Point', 'coordinates': (1.0, 1.0)}
 ```
+
+Conversely, it is possible to encode GeoJSON or Geo Interfaces to GML
+
+
+```python
+>>> from pygml.v32 import encode_v32
+>>> from lxml import etree
+>>> tree = encode_v32({'type': 'Point', 'coordinates': (1.0, 1.0)}, 'ID')
+>>> print(etree.tostring(tree, pretty_print=True).decode())
+<gml:Point xmlns:gml="http://www.opengis.net/gml/3.2" srsName="urn:ogc:def:crs:OGC::CRS84" gml:id="ID">
+  <gml:pos>1.0 1.0</gml:pos>
+</gml:Point>
+
+>>>
+```

pygml/axisorder.py

@@ -1,6 +1,36 @@
+# ------------------------------------------------------------------------------
+#
+# Project: pygml <https://github.com/geopython/pygml>
+# Authors: Fabian Schindler <[email protected]>
+#
+# ------------------------------------------------------------------------------
+# Copyright (C) 2021 EOX IT Services GmbH
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies of this Software or works derived from this Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+# ------------------------------------------------------------------------------
+
+
 import re
+from typing import Union
 
-# copied from https://github.com/geopython/OWSLib/blob/a9c1be25676ab530fd0327c2450922f288ca25f4/owslib/crs.py
+# copied from:
+# https://github.com/geopython/OWSLib/blob/a9c1be25676ab530fd0327c2450922f288ca25f4/owslib/crs.py
 AXISORDER_YX = {
     4326, 4258, 31466, 31467, 31468, 31469, 2166, 2167, 2168, 2036, 2044, 2045,
     2065, 2081, 2082, 2083, 2085, 2086, 2091, 2092, 2093, 2096, 2097, 2098,
@@ -158,22 +188,40 @@
     r'http://www\.opengis\.net/gml/srs/epsg\.xml\#|'
     r'urn:EPSG:geographicCRS:|'
     r'urn:ogc:def:crs:EPSG::|'
-    r'urn:ogc:def:crs:EPSG:)([0-9]+)'
+    r'urn:ogc:def:crs:OGC::|'
+    r'urn:ogc:def:crs:EPSG:)([0-9]+|CRS84)'
 )
 
 
-def is_crs_yx(crs: str) -> bool:
-    """
+def get_crs_code(crs: str) -> Union[int, str]:
+    """ Extract the CRS code from the given CRS identifier string,
+        which can be one of:
           * EPSG:<EPSG code>
           * http://www.opengis.net/def/crs/EPSG/0/<EPSG code> (URI Style 1)
           * http://www.opengis.net/gml/srs/epsg.xml#<EPSG code> (URI Style 2)
           * urn:EPSG:geographicCRS:<epsg code>
           * urn:ogc:def:crs:EPSG::<EPSG code>
+          * urn:ogc:def:crs:OGC::<EPSG code>
           * urn:ogc:def:crs:EPSG:<EPSG code>
+
+        Returns the code as an integer in case of EPSG code or as the
+        string 'CRS84'
     """
     match = RE_CRS_CODE.match(crs)
     if not match:
         raise ValueError('Failed to retrieve CRS code')
 
-    code = int(match.groups()[1])
+    value_group = match.groups()[1]
+
+    try:
+        return int(value_group)
+    except ValueError:
+        return value_group
+
+
+def is_crs_yx(crs: str) -> bool:
+    """ Determines whether the given CRS uses Y/X (or latitude/longitude)
+        axis order.
+    """
+    code = get_crs_code(crs)
     return code in AXISORDER_YX

pygml/dimensionality.py

@@ -0,0 +1,49 @@
+# ------------------------------------------------------------------------------
+#
+# Project: pygml <https://github.com/geopython/pygml>
+# Authors: Fabian Schindler <[email protected]>
+#
+# ------------------------------------------------------------------------------
+# Copyright (C) 2021 EOX IT Services GmbH
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies of this Software or works derived from this Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+# ------------------------------------------------------------------------------
+
+from typing import Optional
+from collections.abc import Sequence
+
+from .types import GeomDict
+
+
+def get_dimensionality(geometry: GeomDict) -> Optional[int]:
+    """ Returns the dimensionality of a given GeoJSON geometry.
+        This is obtained by descending into the first coordinate
+        and using its length.
+        When no coordinates can be retrieved (e.g: in case of
+        GeometryCollections) None is returned.
+    """
+
+    coordinates = geometry.get('coordinates')
+
+    if coordinates:
+        # drill down into nested coordinates
+        while isinstance(coordinates[0], Sequence):
+            coordinates = coordinates[0]
+        return len(coordinates)
+    return None

pygml/georss.py

@@ -25,16 +25,19 @@
 # THE SOFTWARE.
 # ------------------------------------------------------------------------------
 
-from typing import List
+from pygml.axisorder import get_crs_code
+from typing import Callable, List
 
 from lxml import etree
+from lxml.builder import ElementMaker
 
 from .basics import (
     parse_pos, parse_poslist, swap_coordinate_xy, swap_coordinates_xy
 )
+from .dimensionality import get_dimensionality
 from .types import GeomDict
 from .pre_v32 import NAMESPACE as NAMESPACE_PRE32, parse_pre_v32
-from .v32 import NAMESPACE as NAMESPACE_32, parse_v32
+from .v32 import NAMESPACE as NAMESPACE_32, encode_v32, parse_v32
 from .v33 import NAMESPACE as NAMESPACE_33_CE, parse_v33_ce
 
 
@@ -120,3 +123,73 @@ def parse_georss(element: Element) -> GeomDict:
         result['bbox'] = bbox
 
     return result
+
+
+GEORSS = ElementMaker(namespace=NAMESPACE, nsmap=NSMAP)
+
+GmlEncoder = Callable[[GeomDict, str], Element]
+
+
+def encode_georss(geometry: GeomDict,
+                  gml_encoder: GmlEncoder = encode_v32) -> Element:
+    """ Encodes a GeoJSON geometry as a GeoRSS ``lxml.etree.Element``.
+        Tries to use the native GeoRSS elements ``point``, ``line``,
+        or ``polygon`` when possible. Falls back to ``georss:where``
+        with using the ``gml_encoder`` function (defaulting to GML 3.2):
+          - MultiPoint, MultiLineString, MultiPolygon geometries
+          - Polygons with interiors
+          - GeometryCollections
+          - any geometry with CRS other than CRS84 or EPSG:4326
+          - when dealing with >2D geometries
+    """
+    type_ = geometry['type']
+    coordinates = geometry.get('coordinates')
+    crs = geometry.get('crs')
+    dims = get_dimensionality(geometry)
+
+    code = None
+    if crs:
+        crs_name = crs.get('properties', {}).get('name')
+        code = get_crs_code(crs_name)
+
+    if code in (None, 4326, 'CRS84') and dims == 2:
+        if type_ == 'Point':
+            return GEORSS(
+                'point',
+                ' '.join(
+                    str(v) for v in swap_coordinate_xy(coordinates)
+                )
+            )
+
+        elif type_ == 'LineString':
+            return GEORSS(
+                'line',
+                ' '.join(
+                    ' '.join(
+                        str(v) for v in coordinate
+                    ) for coordinate in swap_coordinates_xy(coordinates)
+                )
+            )
+
+        elif type_ == 'Polygon':
+            # only exterior
+            if len(coordinates) == 1:
+                return GEORSS(
+                    'polygon',
+                    ' '.join(
+                        ' '.join(
+                            str(v) for v in coordinate
+                        ) for coordinate in swap_coordinates_xy(coordinates[0])
+                    )
+                )
+
+    # fall back to GML encoding when we have:
+    #   - MultiPoint, MultiLineString, MultiPolygon geometries
+    #   - Polygons with interiors
+    #   - GeometryCollections
+    #   - any geometry with CRS other than CRS84 or EPSG4326
+    #   - when dealing with >2D geometries
+    return GEORSS(
+        'where',
+        gml_encoder(geometry, 'ID')
+    )