Convert a GML Polygon into GeoJSON.
npm install parse-gml-polygonConvert a GML Polygon into a GeoJSON geometry. Accepts the format of xml-reader (with the preserveMarkup flag) as input. Works with a subset of GML 3.3.
Parsing GML is a nightmare. This module tries to parse most of the mentioned ways to encode a polygon. I don't intend to cover all of them though. To quote the wonderful GML madness article by Even Rouault:
> But, you may have noticed that the child of a CompositeCurve is a curveMember, which is also the parent of the CompositeCurve. So we may put a CompositeCurve inside a CompositeCurve.
> […] or maybe you prefer to use gml:surfaceMembers (with a final s) instead of a gml:surfaceMember […]
> To conclude, we should mention that the authors of the GML specification have admitted that encoding polygons was a bit too complicated.
!ISC-licensed
``shell`
npm install parse-gml-polygon
`js
const h = require('hyper-xml')
const parse = require('parse-gml-polygon')
const el = h('gml:Polygon', {'gml:id': 'some-id'}, [
h('gml:exterior', [
// triangle of 0|0 0|3 3|3
h('gml:LinearRing', [
h('gml:posList', ['0 0 0 3 3 3 0 0'])
])
]),
h('gml:interior', [
// triangle of 1|1 1|2 2|2
h('gml:LinearRing', [
h('gml:posList', ['1 1 1 2 2 2 1 1'])
])
])
])
const geometry = parse(el)
console.log(geometry)
`
`js`
{
type: 'Polygon',
coordinates: [
[ // exterior/outer shape
[0, 0],
[0, 3],
[3, 3],
[0, 0]
],
[ // interior/inner shape
[1, 1],
[1, 2],
[2, 2],
[1, 1]
]
]
}
This library consumes a tree structure corresponding to XML. xml-reader parses XML into these structures. With hyper-xml, you can create them manually.
Look at these code examples to understand how to use parse-gml-polygon:
- from an XML/GML string: examples/xml-string.js
- from an XML/GML file: examples/xml-file.js
- creating a tree manually: examples/hyper-xml.js
`js`
parseGmlPolygon(tree, { transformCoords: noTransform, stride: 2}) => GeoJSON
Second argument is a map of options:
- You may optionally pass in a transformCoords function, e.g. to translate them into WGS84. The default transform is (x, y) => [x, y].stride
- specifies the default number of values that each point in the polygon has. A stride of 3 would correspond to a polygon in a 3D coordinate system. srsDimension
Please note that this value can be overridden by the attribute. stride
Default value of is 2.
-
- , which is deprecatedtodo
- see s in the tests
If you have a question or have difficulties using parse-gml-polygon`, please double-check your code and setup first. If you think you have found a bug or want to propose a feature, refer to the issues page.