Can Draw Order of Polygons Be Controlled in KML? - kml

Question

I have adjacent polygons (clampToGround) where a portion of the boundaries overlap. I would like to be able to control which one appears on top. The only method I've found to work thus far is to list the polygon placemarks in stack order (last on list appears on top). However, I'd like to organize the placemarks based on other logic and would like a coding method to specify which polygon is on top.
Note, I've also tried using relativeToGround and small elevation differences, but that leads to potions of the polygons fill to disappear beneath the topography.

Answer 1

You can specify <gx:drawOrder> element (which is a Google Earth KML extension) to order polygons as well as lines and rings in your KML.
Note the documentation (see below) only specifies LineStrings but also works for Lines, LinearRings, and Polygons. Anywhere "LineStrings" is mentioned below just replace it with Lines, Rings, and Polygons. The drawOrder support for Polygons is undocumented but was reported as an issue.
KML Documentation:
<gx:drawOrder>
"An integer value that specifies the order for drawing multiple line
strings. LineStrings drawn first may be partially or fully obscured by LineStrings with a later (or higher) draw order. This element may be required in
conjunction with the <gx:outerColor> and <gx:outerWidth> elements in
<LineStyle> when dual-colored lines cross each other."
Note this will only work in clients that support the Google Earth KML extensions.
In example below, the Red polygon is drawn over the blue polygon. To make the blue polygon draw over the red one change its drawOrder value to a higher number.
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2">
<Document>
<Placemark>
<name>Red Polygon</name>
<description>gx:drawOrder=3</description>
<Style>
<LineStyle>
<color>ff000000</color>
</LineStyle>
<PolyStyle>
<color>ff0000ff</color>
</PolyStyle>
</Style>
<Polygon>
<gx:drawOrder>3</gx:drawOrder>
<tessellate>1</tessellate>
<outerBoundaryIs>
<LinearRing>
<coordinates>
14.456906,37.345497,0 14.949769,37.346531,0
14.960918,37.987563,0 14.45089,37.987521,0
14.456906,37.3455,0
</coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>
<Placemark>
<name>Blue Polygon</name>
<description>gx:drawOrder=2</description>
<Style>
<LineStyle>
<color>ff000000</color>
</LineStyle>
<PolyStyle>
<color>ffff0000</color>
</PolyStyle>
</Style>
<Polygon>
<gx:drawOrder>2</gx:drawOrder>
<tessellate>1</tessellate>
<outerBoundaryIs>
<LinearRing>
<coordinates>
14.83626,38.016863,0 14.835535,37.645589,0
15.47025,37.589266,0 15.470457,38.019158,0
14.83626,38.016862,0
</coordinates>
</LinearRing>
</outerBoundaryIs>
</Polygon>
</Placemark>
</Document>
</kml>