Drawing Dashed Routes behind Buildings in Birds eyes

Recently I was asked how to draw route lines in Birds eye so that they become dashed when behind a building. Needless to say this turned into a pretty good brain teaser as the dashed lines on the Birds eye tiles are part of the image. So after some thought the possible methods that I could think of included:

  • Use the 3D API of Virtual earth to determine where buildings are and see if based on the Birds eye orientation if a building is between the camera and the road. This could be done ahead of time and the data stored. It could also be done programmatically if the user is using 3D. This would require a significant amount of development. This method would also only work where 3D models exist.
  • Create regions where tall buildings exist and then if a polyline is drawn in this region the direction in which the line runs can be determined. If the road runs horizontal more horizontal than vertical to the current birdseye orientation then make the line dashed. This method would be easier to develop and could be used dynamically, but would not be perfect. However, looking at some Birds eye imagery I’ve noticed that the dashed lines do not always show up when they should.

I ended up putting together some sample code on how to do the second method. This is were the code for the article "Dashed Polylines in Virtual Earth" originated from.

What the code does is defines a set of circular regions where tall buildings are known to exist (user defined) and then calculates the heading of a section of a path (http://rbrundritt.spaces.live.com/blog/cns!E7DBA9A4BFD458C5!393.entry). If heading is more perpendicular than parallel to the Birds eye orientation the line is drawn as a dashed line.

As an added bonus, polylines done appear to be rendered when added in Birds eye mode. So the map needs to be flipped to a different map style, the polyline added, and then flipped back to Birds eye. For simplicity I used an array of points for my route. An actual VE route can be used when using client tokens and retrieving the route geometry (http://rbrundritt.spaces.live.com/blog/cns!E7DBA9A4BFD458C5!782.entry).

The complete source code for this sample can be found here: http://cid-e7dba9a4bfd458c5.skydrive.live.com/self.aspx/VE%20Sample%20code/dashedRoutes.zip

Here is a screen shot of this code in action:

image

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