FeatureCollection¶

FeatureCollection objects can be used to manipulate features in several ways. Typically, you would use member functions such as fc.merge(), fc.combine() and fc.plot() to perform these manipulations.

Reading in Features¶

A FeatureCollection can be read from a file with the function geometric_features.feature_collection.read_feature_collection():

from geometric_features import read_feature_collection

fc = read_feature_collection('features.geojson')

Add a Feature¶

To add a single feature to a FeatureColleciton, use geometric_features.feature_collection.FeatureCollection.add_feature():

fc.add_feature(feature)

feature is a dictionary describing a single Feature.

Merging Features¶

A FeatureCollection fc2 can be merged into another colleciton fc1: with geometric_features.feature_collection.FeatureCollection.merge():

fc1.merge(fc2)

If the same feature name is found in both, the original feature from fc1 is retained.

Plotting Features¶

A FeatureCollection can be plotted on a given map projeciton with geometric_features.feature_collection.FeatureCollection.plot():

import matplotlib.pyplot as plt

# plot the features in fc on a cylindrical projection
fig = fc.plot('cyl')

plt.show()

Tag Features¶

All the features in a FeatureCollection can be tagged with one or more tags using geometric_features.feature_collection.FeatureCollection.tag():

fc.tag(['tag1', 'tag2'])

These features can later be split into the :ref: GemoetricData direcory (see Adding New Features) and uploaded to the GitHub repository. Tags make it easier to combine many features into a feature collection (e.g. individual ocean regions into ocean basins).

Writing out Features¶

To write out a FeatureCollection to a geojson file, call geometric_features.feature_collection.FeatureCollection.to_geojson()

fc.to_geojson('features.geojson')

Set a Group Name¶

To set the groupName property of a FeatureCollection, call geometric_features.feature_collection.FeatureCollection.set_group_name().

fc.set_group_name('Regions Group')

Group names can be used later to identify the features in a collection, e.g. in order to create a mask for that cells in a mesh that belong to the features in that group. The MPAS-Ocean model uses these features to create masks for land and for ocean regions such as ocean basins and Antarctic ice-shelf cavities.

Combine Features¶

Features in a FeatureCollection can be combined (fused together into a single feature) using geometric_features.feature_collection.FeatureCollection.combine():

fcCombined = fc.combine('my feature name')

Difference Features¶

Features in a FeatureCollection can be masked with one or more masking features from another FeatureCollection using geometric_features.feature_collection.FeatureCollection.difference():

fcMasked = fc.difference(fcMask)

In this example, any part of the features in fc that overlap with any of the features in fcMask is removed in the resulting fcMasked.

Simplify Features¶

Sometimes, features are made up of segments or polygons with tiny edges that add little relevant detail to the features but make the files describing them needlessly large. In such cases, the features can be simplified by calling geometric_features.feature_collection.FeatureCollection.simplify() with and appropriate length scale (in degrees latitude/longitude) over which the feature may be modified to make it simpler. If a length scale of zero is used, the feature will be simplified without any modification tot he shape being described (so that only edges or polygons that are truly reduntant will be removed).

fcSimplified = fc.simplify(1.0)

Fix Features at +/- 180¶

Valid geojson shapes should not cross the “antimeridian”, the location where 180 degrees longitude meets -180 degrees. Often, it isn’t practical to contstruct a feature’s geometry from the start in this way, so this function provides a bit of a hack for removing a tiny sliver of the feature around the antimeridian so that the resulting shape remians between -180 and 180 degrees longitude.

geometric_features.feature_collection.FeatureCollection.fix_antimeridian()

fcFixed = fc.fix_antimeridian()