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User-defined marker: Markers that you have full control over.
Special markers: These are generated by the system.
Sphere marker: This isn’t defined by the user but is rather defined by AerialSphere. This always uses an icon that looks like a green ball or sphere. When a sphere marker is clicked, its associated sphere is loaded.
Query marker: The marker that is added either when an end-user makes a search using the search bar, or right-clicks in the sphere. This type of marker is not limited by any other restrictions (such as setCustomMarkerDistance or setPanoMarkerList).
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