How to remove border points from InputForm?

Question

I have this code, and it generates the below ListStreamPlot. The second graph is the ListStreamPlot overlaid with the points comprising the ListStreamPlot (extracted after looking at // InputForm); unfortunately, the extracted points also include the border points. These "border points" are not of predictable coordinates, so there doesn't seem to be an easy way to remove them from the set. (I want this code to be as case-inspecific as possible, since I am analyzing many additional data sets.)

Is there a simple way -- perhaps in the original ListStreamPlot code -- to remove the "border points" from the points list?

v3 = ListStreamPlot[vectorsT, StreamStyle -> "Line", StreamPoints -> 
  {{xcorT[[midpoint + 4]], ycorT[[midpoint + 4]]}}]

points = v3[[1, 2, 1]];

xPoints = Transpose[points][[1]]; 
yPoints = Transpose[points][[2]];

pointsOnly = ListPlot[Transpose[Join[{xPoints}, {yPoints}]]] ;

graph 1:

graph 2:

Entire source code

(* Set directory to that of this notebook *)
SetDirectory[NotebookDirectory[]];

(* Import CSV'd data *)
dat = Import["test_data2b.txt", "CSV"];

(* Divide data *)
datAll = Flatten[Partition[dat[[1]], 7]];
datAllCpy = datAll;

(* Divide data into components *)
(* ID *)

ID = Flatten[Partition[datAll, 1, 7]];
datAll = RotateLeft[datAll];

(* Longitude *)
LONG = Flatten[Partition[datAll, 1, 7]];
datAll = RotateLeft[datAll];

(* Latitude *)
LAT = Flatten[Partition[datAll, 1, 7]];
datAll = RotateLeft[datAll];

(* SFC_SPD *)
SPD1 = Flatten[Partition[datAll, 1, 7]];
datAll = RotateLeft[datAll];

(* SPF_SPD _KT *)
SPD2 = Flatten[Partition[datAll, 1, 7]];
datAll = RotateLeft[datAll];

(* SFC_SPD _MP *)
SPD3 = Flatten[Partition[datAll, 1, 7]];
datAll = RotateLeft[datAll];

(* SFC_DIR *)
DIR = Flatten[Partition[datAll, 1, 7]];

(* Restore original list *)
datAll = datAllCpy;

(* Make longtitudes negative *)
LONG = Abs[LONG];
LONG = 0 - LONG;

(* Convert from degrees to radians *)
DIR = DIR *(2 Pi/360);

(* Graph data as vectors *)
xcor = LONG;
ycor = LAT;
xvc = SPD1*Cos[DIR]; 
yvc = SPD1*Sin[DIR];
vectors = Table[{{xcor[[i]], ycor[[i]]}, {-yvc[[i]], -xvc[[i]]}}, {i, 1, Length[xcor]}];

(* Calculate midpoint of data *)
midpoint = Flatten[Position[SPD1, 0.]][[1]];

(* Transpose all points to be around origin *)
LONGT = LONG - (LONG[[midpoint]]);
LATT = LAT - LAT[[midpoint]]; 

(* Graph data as vectors *)
xcorT = LONGT;
ycorT = LATT;
xvcT = SPD1*Cos[DIR]; 
yvcT = SPD1*Sin[DIR];
vectorsT = Table[{{xcorT[[i]], ycorT[[i]]}, {-yvcT[[i]], -xvcT[[i]]}}, {i, 1, Length[xcor]}];

v3 = ListStreamPlot[vectorsT, StreamStyle -> "Line", StreamPoints -> {{xcorT[[midpoint + 4]], ycorT[[midpoint + 4]]}}]

points = v3[[1, 2, 1]]; 

xPoints = Transpose[points][[1]]; 
yPoints = Transpose[points][[2]];

pointsOnly = ListPlot[Transpose[Join[{xPoints}, {yPoints}]]] ;

Show[v3, pointsOnly]

Answer 1

You can extract the Line first, then extract the points on the line:

pts = Cases[v3,
   GraphicsComplex[c__] :>
    Cases[Normal[GraphicsComplex[c]],
     Line[pts_] :> pts, Infinity],
   Infinity] // Flatten[#, 2]& ;
Graphics[{Red, Point[pts]}, Frame -> True ]

Answer 2

You could abuse the StreamColorFunction for this goal

res=
Reap[
  v3 = ListStreamPlot[vectorsT, 
          StreamStyle -> "Line", 
          StreamPoints -> {{xcorT[[midpoint + 4]], ycorT[[midpoint + 4]]}}, 
          StreamColorFunction -> ((Sow[{#1, #2}]; None) &)
       ]
];

ListPlot[res[[2]], AspectRatio -> Automatic]