oegeo

I spent a couple of days building a ‘mashup’ application that shows the 360 degree panorama photos from CycloMedia on top of the MS Virtual Earth Bird’s Eye views. The end result is a rich visual experience of a geographical location (see screenshot on the right)

In this document I summarize the challenges and useful experiences I gained with the VE API.

• Coming from a C# background, one would expect more control over objects through properties instead of getter / setter methods which clutter up the API. You get lots of methods like map.GetZoomLevel() and map.SetZoomLevel()
• Implementing a custom icon is very simple, as long as you stay in 2D mode where you can use the SetCustomIcon() method on a shape.
• The documentation (http://msdn2.microsoft.com/en-us/library/bb429565.aspx) is not always correct:
• The VEShape control has no ID property you can set. It has a Title property that you can get and set, but that will also appear in the info box. The JS Prototype construct came to my rescue: I added a custom property to the VEShape object to hold the Cyclomedia ID …

VEShape.prototype.CycloID = null;

• … and a function to get a pointer to a VEShape corresponding to a specific Cyclomedia ID.

function findShapeByCycloId(id)
  {
  for(i=0;i<shapeLayer.GetShapeCount();i++)
  {
    shape = shapeLayer.GetShapeByIndex(i);
    if(shape.CycloID == id)
    {
      return shape;
    }
  }
  return null;
}

• For debugging and development purposes, it is convenient to have the entire function that handles the onLoadMap event in a try…catch block, as well as the function that creates the map and is fired by the body.onload event. That should cover most VE exceptions. Still I found that I got unhandled VE Exceptions.

• I had the need for an arrow that indicates the view direction in the CycloScopeLite plugin and thus can be rotated. I solved this by creating a polyline arrow as a VEShape. Its nodes are calculated from the angle value supplied by the ChangeHorzViewDir event fired by the CycloScopeLite control. See result above. This is not a watertight solution though:
  • Sometimes one of the arms of the arrow are not drawn. This behavior is hard to reproduce but seems to occur when sin(angle) or cos(angle) are close to 0.
  • It doesn’t survive a switch to 3D mode, and won’t reappear when you switch back to 2D mode. It’s not clear to me why.
  • Furthermore, a VEShape needs to be calculated in ground coordinates and its size is thus dependent on the zoom level. A scale factor is calculated to deal with this:

var scalefactor = (map.GetMapStyle() == VEMapStyle.Birdseye)?(scalefactor = 0.0001 * (2.5-map.GetZoomLevel())):(scalefactor = 0.0001 * (19.5-map.GetZoomLevel()));

• It is clear from the code snippet above that the value returned by map.GetZoomLevel() has a different range for Aerial/Road modes and for Bird’s Eye mode. Aerial/Road has 1-19, while BE has only 1 and 2.

I will write a folluw-up article on some of the more interesting topics I challenged.