Give label to KML polygon

[burnin...@gmail.com]

I have been trying to figure out how to add a label to a polygon from a KML file, but I'm having no luck. Since the polygon doesn't have a position attribute, I'm unsure how to place the labels, since I want them approximately in the center of the polygons.

[Scott Reynolds]

You have to specify both a Polygon and a Point inside a MultiGeometry.

<?xml version="1.0" encoding="UTF-8"?>

<kml xmlns="http://www.opengis.net/kml/2.2">

<Document>

<Style id="polygonStyle">

<IconStyle>

<!-- Hide the pushpin -->>

<scale>0.0</scale>

</IconStyle>

<LabelStyle>

<color>ffffff00</color>

<colorMode>normal</colorMode>

</LabelStyle>

<PolyStyle>

<color>4400ff00</color>

<colorMode>normal</colorMode>

<fill>1</fill>

<outline>1</outline>

</PolyStyle>

</Style>

<Placemark>

<name>A Polygon with label</name>

<styleUrl>#polygonStyle</styleUrl>

<MultiGeometry>

<Point>

<coordinates>0.0,0.0,0.0</coordinates>

</Point>

<Polygon>

<outerBoundaryIs>

<LinearRing>

<coordinates>

10.0,10.0,0.0

10.0,-10.0,0.0

-10.0,-10.0,0.0

-10.0,10.0,0.0

10.0,10.0,0.0

</coordinates>

</LinearRing>

</outerBoundaryIs>

</Polygon>

</MultiGeometry>

</Placemark>

</Document>

</kml>

[burnin...@gmail.com]

Is the point supposed to be the "center" of the polygon? This is not ideal, as this would then have to be manual

[burnin...@gmail.com]

I should also add I'm getting the label from the ExtendedData

[Rachel Hwang]

Hi there,

Unfortunately manual is the way to go here, since polygons only take a list of positions in world space. The computation shouldn't be bad though -- you can do something simple like average positions. 

Hope that helps,

- Rachel

[burnin...@gmail.com]

Even doing it manually doesn't center the label in the polygon, it is skewed towards where there are more coordinate points

[Rachel Hwang]

That makes sense if you're doing a simple average. To center, try computing the minimum and maximum coordinates and placing your label in the center (like a bounding box).

[Scott Reynolds]

Placement of the label is a complicated problem.  Think about where you would want to label a horseshoe or a polygon with interior holes.  Also, in a dynamic viewer you might need to re-position the label if it is off-screen but part of the polygon is not.

On Tuesday, June 13, 2017 at 12:55:21 PM UTC-4, burnin...@gmail.com wrote:

[Matthew Amato]

Check out Mapbox's polylabel library: https://github.com/mapbox/polylabel I've had some success in using it with Cesium to generate ideal label positions inside of a polygon.  It's mean for 2D so large polygons sometimes don't have the ideal solution, but I find that it's much more reliable than coming up with your own algorithm.

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