Creating a function takes a list and dynamically modifies that list [duplicate]

I'm trying to create a function that uses a dynamic locatorpane to populate a list with the coordinates of user defined locators (added by alt+clicking). This code works fine:

one = ExampleData[{"TestImage", "Airplane"}] ptsa = {}; ptsb = {}; Button["Reset points", ptsa = {}] LocatorPane[Dynamic[ptsa], Dynamic[ Show[one, Graphics[{ Table[(*draw arrows between locators*) Arrow[{ ptsa[[i]], ptsa[[i + 1]] }], {i, 1, Floor[Length[ptsa], 2], 2} ], Table[ Text[(i + 1)/2, ptsa[[i]] + (ptsa[[i + 1]] - ptsa[[i]])/2 + Cross[ptsa[[i + 1]] - ptsa[[i]]]/ EuclideanDistance[ptsa[[i + 1]], ptsa[[i]]]*10],(*display line # 5 pixels orthogonal to line \ midpoint*) {i, 1, Floor[Length[ptsa], 2], 2} ] }] ] ], LocatorAutoCreate -> True, Appearance -> Style["\[CenterDot]", Medium, Red]] 

That works for the single list: "ptsa" and allows me to insert points into "ptsa" with a point-and-click interface.

However, I need to do this for many different lists (ptsb, ptsc, ptsd, etc). I tried making a function ui[ptsa_] := LocatorPane[...] so I can just do ui[ptsb] in the future, but this simply inserts {} into ptsa, which doesn't help.

I also tried defining the above simply as a = LocatorPane[...] and trying

a /. ptsa -> ptsb 

but that doesn't work either. I'm not sure how to approach this.