To assign geographic context to the this.
Passing -1 as latitude or longitude, the relative value is untouched in the object. This is to easy assignment
of coordinates in more than a single step. If both are -1, nothing happens.
| this |
a FeedItem. |
| latitude |
latitude of the point, or -1 to leave the previous one. |
| longitude |
longitude of the point, or -1 to leave the previous one. |