| 1 | | It may not be necessary to actually calculate the buffer for extending the distance of geometry A to determine whether geometry B is fully included in the buffer for extending the distance of geometry A. Because in reality, the point on geometry A that is closest to geometry B is the one that determines whether geometry B is fully included in the buffer zone of the extended distance of geometry A. We refer to this point as **P1**. |
| 2 | | |
| 3 | | So, we can simplify this problem as "**Is geometry B completely contained within the buffer zone of the extended distance from point P1?**" And the buffer zone of a point is a circle, and we only need to consider its radius. Under what circumstances does a circle contain a geometry? We call the point on geometry B that is farthest from point P1 as **P2**, and finally simplify the problem as "**Is the distance between P1 and P2 less than the distance?**". |
| 4 | | |
| 5 | | Finally, we can obtain the following equivalent formula: |
| 6 | | {{{ST_DFullyWithin(A, B, R) <=> ST_Contains(ST_Buffer(A, R), B) <=> ST_MaxDistance(ST_ClosestPoint(A, B), B) ≤ R}}} |
| 7 | | |
| 8 | | Sorry for the lengthy explanation, and thank you for your patience. |
