計算pcpatch對象中pcpoint所有屬性的平均值，返回新的pcpoint對象。
文法
pcpoint ST_patchAvg(pcpatch pc);參數
| 參數名稱 | 描述 |
| pc | pcpatch對象。 |
樣本
SELECT ST_AsText(ST_PatchAvg(pa)) FROM patches WHERE id = 7;
-------------------------------------
{"pcid":1,"pt":[-126.46,45.54,54.5,5]}