support to workaround antimeridian problems

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Changes
 
+## Unreleased
+
+Added function to translate GeoJSON objects to be "pacific centered".
+
+
 ## [0.4.0] - 2024-06-11
 
 - Enhanced `fixed_geometry`, adding option to fix antimeridian issues.

README.md

@@ -14,12 +14,26 @@ pip install cldfgeojson
 ```
 
 
-## Adding speaker areas to CLDF datasets
+## Creating CLDF datasets with speaker area data in GeoJSON
 
 The functionality in [`cldfgeojson.create`](src/cldfgeojson/create.py) helps adding speaker area
 information when creating CLDF datasets (e.g. with [`cldfbench`](https://github.com/cldf/cldfbench)).
 
 
+## Manipulating geo-referenced images in GeoTIFF format
+
+The [`cldfgeojson.geotiff`](src/cldfgeojson/geotiff.py) module provides functionality related to
+images in [GeoTIFF](https://en.wikipedia.org/wiki/GeoTIFF) format.
+
+
+## Commandline interface
+
+`cldfgeojson` also provides [`cldfbench` sub-commands](https://github.com/cldf/cldfbench?tab=readme-ov-file#commands):
+
+- [`geojson.webmercator`](src/cldfgeojson/commands/webmercator.py)
+- [`geojson.overlay`](src/cldfgeojson/commands/overlay.py)
+
+
 ## `leaflet.draw`
 
 This package contains the [`leaflet.draw`](https://github.com/Leaflet/Leaflet.draw) plugin in the form of `data://` URLs in 

src/cldfgeojson/create.py

@@ -147,6 +147,8 @@ def aggregate(shapes: typing.Iterable[typing.Tuple[str, geojson.Feature, str]],
         typing.List[geojson.Feature],
         typing.List[typing.Tuple[Languoid, list, str]]]:
     """
+    Aggregate features, merging based on same language of family level Glottocode.
+
     :param shapes: Iterable of (feature ID, GeoJSON feature, Glottocode) triples.
     :param glottolog: Glottolog data can be supplied either as `pyglottolog.Glottolog` API object \
     or as glottolog-cldf `pycldf.Dataset`.

src/cldfgeojson/geojson.py

@@ -1,6 +1,6 @@
 import typing
 
-__all__ = ['MEDIA_TYPE', 'Geometry', 'Feature']
+__all__ = ['MEDIA_TYPE', 'Geometry', 'Feature', 'pacific_centered']
 
 # See https://datatracker.ietf.org/doc/html/rfc7946#section-12
 MEDIA_TYPE = 'application/geo+json'
@@ -33,3 +33,50 @@ class Feature(typing.TypedDict, total=False):
     properties: typing.Union[None, JSONObject]
     id: typing.Union[str, float, int]
     bbox: list
+
+
+def pacific_centered(obj: typing.Union[Geometry, Feature]) -> typing.Union[Geometry, Feature]:
+    """
+    Adjust longitudes of coordinates of objects to force a pacific-centered position in place.
+
+    Some mapping tools do not support "continuous worlds", i.e. displaying the same content at
+    360° longitude increments. A typical workaround is "moving" objects to the appropriate "world
+    copy". The same workaround also works for tools like shapely, which do maths in the cartesian
+    plane, to avoid problems caused by the antimeridian.
+
+    For language data, it is often useful to display pacific-centered maps, in order to not cut
+    through the area of any language family. For this purpose, 154°E is a suitable central
+    longitude, because the cut at 26°W does not cut through any macroareas. See
+    https://en.wikipedia.org/wiki/154th_meridian_east and
+    https://en.wikipedia.org/wiki/26th_meridian_west
+
+    :return:
+    """
+    PACIFIC_CENTERED = 154
+
+    def fix_position(pos):
+        pos = list(pos)
+        if pos[0] <= PACIFIC_CENTERED - 180:
+            # Anything west of 26°W is moved by 360°.
+            pos[0] += 360
+        return pos
+
+    geom = obj['geometry'] if 'geometry' in obj else obj
+    if geom['type'] == 'Point':
+        # Point -> [lon, lat]
+        geom['coordinates'] = fix_position(geom['coordinates'])
+    elif geom['type'] in {'MultiPoint', 'LineString'}:
+        # MultiPoint -> [[lon, lat]..]
+        # LineString -> [[lon, lat]..]
+        geom['coordinates'] = [fix_position(pos) for pos in geom['coordinates']]
+    elif geom['type'] in {'Polygon', 'MultiLineString'}:
+        # Polygon -> [[[lon, lat]..]..]
+        # MultiLineString -> [[[lon, lat]..]..]
+        geom['coordinates'] = [[fix_position(pos) for pos in line] for line in geom['coordinates']]
+    else:
+        # MultiPolygon -> [[[[lon, lat]..]..]..]
+        assert geom['type'] == 'MultiPolygon'
+        geom['coordinates'] = [[[
+            fix_position(pos) for pos in line] for line in poly] for poly in geom['coordinates']]
+
+    return obj

tests/test_geojson.py

@@ -0,0 +1,19 @@
+import pytest
+from shapely.geometry import shape
+
+from cldfgeojson.geojson import *
+
+
+@pytest.mark.parametrize(
+    'type_,coords,check',
+    [
+        ('Point', [-170, 0], lambda s: s.x > 0),
+        ('MultiPoint', [[-170, 0], [170, 0]], lambda s: s.centroid.x == 180),
+        ('Polygon', [[[170, 0], [-170, 1], [-170, -1], [170, 0]]], lambda s: s.centroid.x > 180),
+        ('MultiPolygon',
+         [[[[170, 0], [-170, 1], [-170, -1], [170, 0]]]],
+         lambda s: s.centroid.x > 180)
+    ]
+)
+def test_pacific_centered(type_, coords, check):
+    assert check(shape(pacific_centered(dict(type=type_, coordinates=coords))))