[postgis-users] Amoeba Hulls

[Paul Ramsey]

This wouldn't be in vanilla arcview, was it in Network Analyst? The top 
80% of points by drive distance might yield this shape.  Finding the 
points would be straightforward, and then the hull building would be the 
hand-waving part.

P

William Andersen wrote:
> Paul, Steve,
> 
> Thanks for the quick replies, unfortunately it's pretty hard to tell 
> from those images if they match.
> 
> I've done some more digging and it turns out that these shapes were 
> created in Arcview 3.x. The notes I have say...
> 
>  > This approach selects a number of the outliers and joins the extreme 
> points using elliptical arcs.
>  > The arcs are all created in a direction moving out from the store.
> 
> However, I dont see customer points at the discontinuities in the hulls, 
> so it appears that the "extreme points" are perhaps interpolated.
> 
> 
> Will
> 
> On 7/5/06, *Paul Ramsey* <pramsey at refractions.net 
> <mailto:pramsey at refractions.net>> wrote:
> 
>     William,
> 
>     It doesn't look like this is a standard algorithm, but more likely a
>     particular empirical technique provided by the particular software you
>     were using.  So substituting some other technique might yield a
>     different shape entirely... do any of the techniques mentioned here
>     <http://www.geospatial-online.com/geospatialsolutions/article/articleDetail.jsp?id=1348
>     <http://www.geospatial-online.com/geospatialsolutions/article/articleDetail.jsp?id=1348>>
>     sound like what was done to your data?
> 
>     Paul
> 
>     William Andersen wrote:
>      >
>      > I'm fairly new to postgis, and working to automate a number of
>      > processes.
>      >
>      > We are trying to compute market area polygons that look like the
>      > attached image. These were created by some older software.
>      >
>      >
>      > They are referred to as Amoeba Hulls, and they contain 80% of a
>      > store's customers. However I can't find any solid documentation that
>      > would allow me to reproduce them.
>      >
>      > Does anyone have any ideas how these shapes are created or an
>      > alternate name that I might be able to google? Additionally, we may
>      > be in a position to finance the development of this feature.
>      >
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