Frequently Asked Questions

1. Can I have a layer with a transparent background?
2. Why do I need to login to download the KMZ files?
3. How can I draw other polygons on top of the maps?
4. What's this "Unexpected element html" error about?
5. Why are the tiles distorted in lower zoom levels?

1. Can I have a layer with a transparent background?

Yes, you can adjust the opacity of folders, placemarks, overlays and any other KML elements using the slider at the bottom of the "Places" section of the side bar (this screenshot is from an older version of Google Earth, but you will figure it out):

Move mouse over image

Because of that, all maps have a default opacity of 100%. If you want to see more of the satellite imagery base layer, use the slider.

2. Why do I need to login to download the KMZ files?

We are sorry for this, but running this service is quite resource intensive and by using the Google user authentication (super easy on the Google App engine) it is possible to

• balance server load across users,
• exclude malicious use,
• and potentially implement user specific configurations.

Your email address will not be sold to others or used in any other unfriendly way.

3. How can I draw other polygons on top of the maps?

Unfortunately, it is not possible to display KML polygons on top of the map overlays of this site, because polygons don't interact nicely with ground overlays (this problem is not specific to this application).

This is an example of how a single map tile is displayed using a KML GroundOverlay in your Google Earth client:

<?xml version="1.0" ?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <GroundOverlay>
    <name>Map tile for Bing Maps Road</name>
    <Icon>
      <href>http://ecn.t5.tiles.virtualearth.net/tiles/r0230102033300.png?g=414&amp;shading=hill</href>
    </Icon>
    <drawOrder>1</drawOrder>
    <visibility>1</visibility>
    <LatLonBox>
      <north>37.8575071563</north>
      <south>37.8228024335</south>
      <west>-122.475585938</west>
      <east>-122.51953125</east>
    </LatLonBox>
  </GroundOverlay>
</kml>

You can try it yourself (it's north of the San Francisco Golden Gate bridge): map-tile-example.kml

This is an example of a KML Polygon on top of that (polygon-example.kml ):

<?xml version="1.0" ?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <Placemark>
    <name>Polygon relative to ground</name>
    <Style>
      <PolyStyle>
        <color>aaff0000</color>
        <outline>0</outline>
      </PolyStyle>
    </Style>
    <Polygon>
      <altitudeMode>relativeToGround</altitudeMode>
      <outerBoundaryIs>
        <LinearRing>
          <coordinates>-122.47,37.85,0 -122.51,37.82,0 -122.47,37.82,0 -122.47,37.85,0</coordinates>
        </LinearRing>
      </outerBoundaryIs>
    </Polygon>
  </Placemark>
</kml>

When the altitudeMode of the polygon is set to clampToGround, then the polygon will be hidden by active map overlays. When the mode is relativeToGround (as in the example above), then result looks like below, which is not very useful:

There is, however, a workaround. When your polygons are simple geometric shapes (such as a triangle in the example above), then you could make transparent PNG images (example:blue-triangle.png) out of them and display them as ground overlays with a high drawOrder on top of the map tiles (ground-overlay-example.kml ):

<?xml version="1.0" ?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <GroundOverlay>
    <name>Ground overlay with draw order</name>
    <drawOrder>99</drawOrder>
    <Icon>
      <href>http://ge-map-overlays.appspot.com/images/blue-triangle.png</href>
    </Icon>
    <LatLonBox>
      <north>37.85</north>
      <south>37.82</south>
      <east>-122.47</east>
      <west>-122.51</west>
    </LatLonBox>
  </GroundOverlay>
</kml>

Which then yields a quite acceptable result:

If you have other ideas how to get this working, please leave them in the comments below

4. What's this "Unexpected element html" error about?

Some users get this Error while parsing file ... at line1, column 121: Unexpected element "html" message:

If you see this, then you managed to download a web page instead of the intended .kmz file. The most likely explanation is that you tried to download the kmz file by right-clicking on the link while not being logged in (and thus downloaded the page that asked you to login).

I changed the .kmz file links of this web site to make this more unlikely to happen, and if you try do download one of our .kmz files from an external site, please make sure you don't right-click them.

5. Why are the tiles distorted in lower zoom levels?

In the screen shot below the map overlay shows the the southern border of Russia much further south than it actually is (yellow line):

This is because all map sources of this site use a spherical Mercator projection (also known as EPSG:900913, EPSG:3857, or "Google projection"), whereas Google Earth uses the WSG84 coordinate system. And while the positions of the corners of each tile are accurately transformed between the two systems, it is not possible to somehow "stretch" the tiles themselves in order to better match the ground. But from zoom level 6 or 7 on this problem is almost neglectable.

Comments

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