Google Earth Plugin not exact coordinates

Question

I've got quite strange google earth plugin behaviour. I get the camera position from the plugin to create some KML with coordinates, then I store it in database. When I reload the page, then it reads the kml, inserts it inside some other string - as a result I've got a string with whole kml document inside my javascript code. Then I load it into the plugin. Usually everything works, however after loading I see two things:

The coordinates returned by the API are not the same I have in the kml I'm loading
The camera position is sometimes moved a little bit, which causes errors like: I've got a camera inside a building, and after a couple of page refreshing, the camera suddenly is outside the building.

Do you have any hints how this could be fixed?

Example:

I've created a document, and inserted this camera tag inside:

<Camera>
  <gx:ViewerOptions><gx:option name='streetview'></gx:option></gx:ViewerOptions>
  <longitude>2.1201209999999993</longitude>
  <latitude>48.80452499999986</latitude>
  <altitude>2.4999999991174264</altitude>
  <heading>22.795249807940547</heading>
  <tilt>82.25987544961218</tilt>
  <altitudeMode>relativeToGround</altitudeMode>
</Camera>

Then I loaded it into the plugin, and asked to fly there. When it stopeed flying, I got the coordinates using copyAsCamera() and the latitude was changed to 48.8044078508718.

The difference is not huge, just 0.000117149 but as a result it is showing a totally different place (a different room in the palace.

I'm trying to get exactly the same place, as written in the coordinates.

You would need to show your actual code or at least and example of the issue. It is impossible to say without seeing. — Fraser
No, that is not an example. You should follow this guide when asking for help with code - sscce.org — Fraser
I don't think I'm going to place here the whole application code. So once again: I load e.g. this kml gist.github.com/szymong/45bf4b1fc4fec78ef7e6 when plugin stops flying, the camera is at this place, or another. I have no idea why it doesn't fly to the same place all the time. What's more, when I get the viewchangeend event and read the camera position with ge.getView().copyAsCamera(ge.ALTITUDE_RELATIVE_TO_GROUND).getLongitude() then I get a little bit different numbers than in the original KML. — Szymon Lipiński
And yes, I've also cut the coordinates to 6 decimal places - it behaves the same. — Szymon Lipiński
If you can't or won't show a simple example of the problem then it is impossible to say what is happening. It could be any number of reasons. — Fraser

Fraser Fraser · Accepted Answer · 2013-12-18T19:55:58

I have rewritten the answer to cover the various points you have made and the example you have provided.

street view

The KML data is setting <gx:ViewerOptions> to enter street view mode based on the camera. The key words being based on - a street view is an approximation. Things like the camera tilt and heading are no longer applicable as they are replaced by a SteeetView POV object. Further to that you can't guarantee that a camera at any given latitude and longitude will actually enter street view at the same given latitude and longitude.

relativeToGround and terrain data

Using altitude mode relativeToGround can cause the issue you are seeing. This is because the terrain data hasn't always finished streaming when the relatively positioned element (in your case a camera) is added.

To be clear you should use <altitudeMode>absolute</altitudeMode> and ge.ALTITUDE_ABSOLUTE.

The example you provided uses both <altitudeMode>relativeToGround</altitudeMode> and ge.ALTITUDE_RELATIVE_TO_GROUND.

You could also try disabling the terrain data by turning off the terrain layer, i.e.

ge.getLayerRoot().enableLayerById(ge.LAYER_TERRAIN, false);

multiple viewchangeend events

The viewchangeend event may fire in the middle of a viewchange, especially if the plugin pauses for a brief period during the change. Your markup is triggering street view mode which causes this to happen.

You can resolve this by using setTimeout to throttle the viewchangeend event like so.

var timer = null;
google.earth.addEventListener(ge.getView(), 'viewchangeend', function(){
  if(timer){
    clearTimeout(timer);
  }
    timer = setTimeout(eventHandler, 100);
  }
);

see: https://developers.google.com/earth/documentation/events#event_listeners

Tilt discrepancy

The plugin automatically "swoops" at ground level so that it moves from looking straight down (0 degrees tilt) to straight along the horizon (90 degrees tilt). This is what is causing the discrepancy in the tilt value in the view. You are viewing objects at ground level and so the view is being automatically set - this can't be disabled.

Storing and outputting KML data

Take a look through this document, it gives some really good information of storing coordinate data and covers points like the one I mentioned - A Database Driven Earth App.

.

Google Earth Plugin not exact coordinates

1 Answers