I have a list of $\{x,y,z\}$ pairs representing points in $R^3$. For every unique value of $z$ there are many $\{x,y\}$ pairs defining a polygon/contour in that particular $z$-plane. My dataset looks like this:

    Take[ptv, 3]
    (*{{61.52, -217.26, -80}, {63.48, -217.64, -80}, {65.43, -217.64, -80}}*)

These are coordinates of points residing on the $z=-80$ plane. There are other pairs for $z=-75$, $z=-70$, etc. Therefore `ptv` is of the form:

`ptv`: {{$x_1,y_1,-80$}, {$x_2,y_2,-80$}, ..., {$x_k,y_k,-80$}, ..., {$x_1,y_1,-75$}, ..., {$x_m,y_m,-75$}, ...}

My **goal** is to create a 3D surface where:

(1). the points in every $z$-plane are connected into a polygon/contour and
(2). the points in every $z$-plane are connected with their neighbors in the immediately above and below plane.

I have achieved **(1)**, via:

    Graphics3D[{Line[ptv], Point /@ ptv}]

The result looks like this: 
![Plot1][1]

If I, instead, use:

    ListSurfacePlot3D[ptv, AxesLabel -> {"x","y","z"}]

Then I get some ugly artifacts (edges at the boundaries of the volume) as shown here: 
![Plot2][2]

Whereas, I was expecting a more "smooth" surface without any "openings". Any hints on:

1. Whether `ListSurfacePlot3D[]` is the proper function to use (i.e. in the documentation it is mentioned that `ListSurfacePlot3D[]` may "fold" over; perhaps this is why I'm experiencing these ruffles?) or
2. What other alternatives are there to consider ?

**EDIT 1**:
Minimally working example:

    ClearAll["Global`*"];
    ptv = Import["http://leaf.dragonflybsd.org/~beket/ag1", "Table"]
    ListSurfacePlot3D[ptv, AxesLabel -> {"x", "y", "z"}]


**EDIT 2**:
I excluded random $z$-planes to explore the dependence of the produced surfaces on my dataset. There is considerable visual variability in the output, including some *very* irregular images. Here is the code:

    (* Identify the values of z-planes *)
    planes = ({x, y, z} = #; z)& /@ ptv // Union;
    
    (* Generate some random sequences with z-planes-to-be-excluded *)
    excludedPlanes = Table[
        RandomSample[planes, RandomInteger@{1, 4}],
        {k, 1, 20}]] // Union // Reverse;
    
    (* Filter data by discarding points residing on excluded planes *)
    FilterData[p_] := Select[ptv,
        Function[v, And@@(Unequal[v, #]& /@ p)][Last[#]]&]
    
    (* Generate the 3D surfaces *)
    ListSurfacePlot3D[#, AxesLabel->{"x","y","z"}]& /@ FilterData/@ excludedPlanes

And here is a screenshot:

![enter image description here][3]


  [1]: https://i.sstatic.net/YrVbv.png
  [2]: https://i.sstatic.net/QHraN.png
  [3]: https://i.sstatic.net/Bs47c.png