In the part 1 I descrbed an approach for picking stars using a reticle. I wanted to extend this approach to include other objects such as deep-sky objects, planets etc. Background stars have the advantage of being point sources, and selecting a nearby background star is shown in Figure 1.
Figure 1. Reticle selecting the nearest star.
When non-point sources are involved, an intersection test is required and the item is selected if there are no other point sources within a minimum distance, or if the reticle is closer to the center of the non-point source than any other item. The object is highlighted using a rectangular border, as shown below in Figure 2 for M31.
Figure 2. Reticle selecting a deep sky object by intersection.
Deep-sky objects of less than a minimum size in the current field of view are treated similarly to point sources such as background stars (selected based on a minimum distance and highlighted using a circle and marker line), as shown below in Figure 3 for M32.
Figure 3. Reticle selecting a deep sky object of less than a minimum size.
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