Hello,
This is probably more of a feature request unless someone has already done it.
For calibrating the googlemaps radar heading it would be very useful to:
- Display a line on the googlemap showing the center of the radar beam and which rotates with the radar
- Display a crosshair in the center of the panorama window
I think this type of radar "calibration mode" would make it much easier to find the exact heading value.
I am not sure how to accomplish the first part; the second is trivial.
Currently, when calibrating the radar heading, I set fov to a very small value so that I can zoom in to get a very narrow radar beam and a good heading on a landmark. This method works well enough except when I inevitably forget to change the fov back to a reasonable value. 
Cheers,
Joe