Selecting and transforming¶

Filters starting with feat_ take features and return a list of features. Use them to pick the features you want and to prepare their geometries before rendering.

All of them accept a single feature, a list, a dict (values are used) or nested combinations, as well as bare geometries.

Selecting¶

feat_where¶

things | feat_where(prop, value, …)

Keeps the features whose property prop has one of the given values. Use 'id' as prop to match the feature ID.

{{ data.eddm['RunwayMarking'] | feat_where('markingLocation', 'OTHER:PRE_THR') | render_grp }}

feat_exclude¶

things | feat_exclude(prop, value, …)

The opposite of feat_where: drops the features whose property has one of the given values. Useful for leaving out individual segments:

{{ taxilanes['C1']
   | feat_exclude('id', '3e99e6d5-131b-2fe6-e063-15baa8c0aafe')
   | feat_join | render_line('C1') }}

You can also pass a list with *: feat_exclude('id', *excluded_ids).

feat_select_geometry¶

things | feat_select_geometry(name)

AIXM features can have several geometric properties. This filter uses only the one with the given name and drops features that do not have it.

{{ data.eddm['AircraftStand'] | feat_select_geometry('location') | render_symbol('stand') }}

feat_min_area¶

things | feat_min_area(area)

Keeps the features whose area is at least area. Lines and points have no area and are always dropped.

The area is measured in square degrees, so useful values are very small: 0.000000001 removes areas below roughly 8 m² in central Europe. For multi-part features, the total area counts; use feat_explode first to filter individual parts.

{{ buildings | feat_explode | feat_min_area(0.000000001) | render_area('OTHER:REGION') }}

Transforming¶

feat_simplify¶

things | feat_simplify(tolerance)

Simplifies each geometry by removing points that deviate less than tolerance from the simplified shape. The tolerance is given in degrees: 0.000005 is about half a metre. Simplifying makes map files smaller and faster to draw.

{% set default = 0.000005 %}
{{ data.eddm['ApronElement'] | feat_simplify(default) | render_area('OTHER:REGION') }}

feat_explode¶

things | feat_explode

Splits multi-part geometries into one feature per part. Each part keeps the properties of its feature.

feat_join¶

things | feat_join

Merges the lines of all features into as few lines as possible, joining segments that share an end point. The result is a single feature; if the segments are not connected, its geometry has several parts.

• Only lines are joined. Areas and points are skipped with a warning.
• The result keeps only the properties that are the same on all input features.

{{ taxilanes['W1'] | feat_join | feat_simplify(default) | render_line('W1') }}

feat_join_by¶

things | feat_join_by(prop)

Joins features per value of a property, returning one feature per value in the order they first appear. This replaces a loop over a group(...) result:

{# one joined line per taxiway designator, labelled with the designator #}
{% for line in data.eddm['GuidanceLine'] | feat_join_by('designator') %}
    {{- line | render_line(line.properties.designator) }}
{% endfor %}

Features without the property are joined together into one feature.

feat_union¶

things | feat_union

Combines the geometries of all features into one, merging overlapping areas. Like feat_join, the result keeps only the properties shared by all input features.

{{ data.eddm['TaxiwayElement'] | feat_union | feat_simplify(default) | render_area('OTHER:REGION') }}

feat_text_box¶

things | feat_text_box(text=None, prop=None, size=0.00008, per_char=0.00001)

Creates a square box around each label point, for example as a background behind a taxiway label. The box extends size degrees from the point in each direction, plus per_char degrees for every character of the label, given as a fixed text or the name of a property with prop. For lines and areas, a point inside the geometry is used, like for render_text.

{% for name, label in data.eddp_kml['TWYDesig'].items() %}
    {{- label | feat_text_box(text=name) | render_area('OTHER:REGION', color='taxiway') }}
{% endfor %}
COLOR:labels-twy
{% for name, label in data.eddp_kml['TWYDesig'].items() %}
    {{- label | render_text(text=name) }}
{% endfor %}