It is a bit hard to explain every aspect from first time.
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doubleclick will set the max speed and direction of the actor once it triggered
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direction is still based on camera but you can rotate camera and double click in diferent direction ( like you show, but you can rotate camera to choose a different direction)
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sphere is hollow, is just an image with stars, planets etc (like sky_sphere bp where you see clouds)
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camera is with actor all time
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the problem i face at the moment, i when i click the actor moves only on axes Y and X it never goes to Z when i click
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As example if you know game eve online, i try to do that movement with double click.