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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Will<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Did you create this using ArcView 3.x Business
Analyst? If so, the Avenue code is available from that interface. That could
give us a guide on how it was created.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Bruce Rindahl<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
postgis-users-bounces@postgis.refractions.net
[mailto:postgis-users-bounces@postgis.refractions.net] <b><span
style='font-weight:bold'>On Behalf Of </span></b>William Andersen<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, July 05, 2006
2:15 PM<br>
<b><span style='font-weight:bold'>To:</span></b> <st1:PersonName w:st="on">PostGIS
Users Discussion</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [postgis-users]
Amoeba Hulls</span></font><o:p></o:p></p>
</div>
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12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>Steve,<br>
<br>
I think you are onto something.<br>
<br>
There are exactly 101 points in each of the polygons in the (small) sample set
that I have.<br>
<br>
When i get a little more time i'll plot these with 3.6 degree wedges and see if
anything jumps out at me. <br>
<br>
My working theory is that there are a set of rules determining what happens at
each control point. In some cases it's pretty simple as we have enough points
to pick one that includes the 80% points but not the 20% points. In other cases
it seems to be extrapolated from the neighboring points using some kind of
fitted curve. <br>
<br>
Will<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><span class=gmailquote><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>On 7/5/06, <b><span style='font-weight:bold'>Stephen
Woodbridge</span></b> <<a href="mailto:woodbri@swoodbridge.com">woodbri@swoodbridge.com</a>>
wrote:</span></font></span><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Paul,<br>
<br>
Would you not just connect the dots, like this.<br>
<br>
1) determine the 80% points, say by distance or whatever<br>
2) order the points by radial angle increasing and radius decreasing<br>
3) use something like a window say plus/minus 1/2 degree and select the <br>
<st1:PersonName w:st="on">max</st1:PersonName>imum radius in the window and add
that point to the polygon<br>
4) step 1/2 degree and repeat 3)<br>
5) close the polygon<br>
<br>
You probably need to have some special handling if there is a sudden<br>
change in radius to make sure no points get clicked out of the polygon. <br>
<br>
Anyway I think this would be a good start to the algorithm.<br>
<br>
-Steve<br>
<br>
Paul Ramsey wrote:<br>
> Indeed, nice to see that everything can be strung together. I
am trying<br>
> to visualize what a "squishyhull" function would have to do to
work <br>
> though :) It's a not uncommon request... the calculated
equivalent of<br>
> someone squinting and drawing a line around a group of points.<br>
><br>
> P<br>
><br>
> Mike Leahy wrote:<br>
>> Hey there, <br>
>><br>
>> If you can determine the closest 80% of points by whatever criteria,<br>
>> wouldn't you be able to use the convexhull() function? I
just tried<br>
>> this, and it looks okay to me:<br>
>><br>
>> testdb=# select astext(convexhull('MULTIPOINT((0 1),(0 0),(1 0),(1<br>
>> 1))'::geometry));<br>
>> astext<br>
>> --------------------------------<br>
>> POLYGON((0 0,0 1,1 1,1 0,0 0)) <br>
>> (1 row)<br>
>><br>
>> I did the same thing after creating a points table with the separate<br>
>> in individual records with the same overall coordinates in the<br>
>> multipoint example above, and it worked okay too: <br>
>><br>
>> testdb=# select astext(convexhull(collect(p))) from testpoint;<br>
>> astext<br>
>> --------------------------------<br>
>> POLYGON((0 0,0 1,1 1,1 0,0 0))<br>
>> (1 row) <br>
>><br>
>> It wouldn't be too hard to modify this to work using where condition<br>
>> that filters out the records of interest...or maybe on a saved view.<br>
>><br>
>> The only problem is that it wouldn't produce a nice curvy polygon <br>
>> outline like in the sample William provided.<br>
>><br>
>> Regards,<br>
>> Mike<br>
>><br>
>> Paul Ramsey wrote:<br>
>>> So my guess is that you use drive-time to segment your population
of <br>
>>> customers relative to the store into the "nearest X%"
and then draw a<br>
>>> "shape" around that cloud of points. And
drawing the shape is the<br>
>>> "fun" part. <br>
>>><br>
>>> William Andersen wrote:<br>
>>>> It appears to be the same as this functionality in Business
Analyst<br>
>>>><br>
>>>> <a
href="http://www.esri.com/software/arcgis/extensions/businessanalyst/about/customer-market.html">http://www.esri.com/software/arcgis/extensions/businessanalyst/about/customer-market.html</a><br>
>>>> <<a
href="http://www.esri.com/software/arcgis/extensions/businessanalyst/about/customer-market.html">http://www.esri.com/software/arcgis/extensions/businessanalyst/about/customer-market.html
</a>><br>
>>>><br>
>>>><br>
>>>> I thought this was done using some older version of Arcview,
but i'm<br>
>>>> not very familiar with esri's offerings.<br>
>>>><br>
>>>> Will<br>
>>>><br>
>>>> On 7/5/06, *Paul Ramsey * <<a
href="mailto:pramsey@refractions.net">pramsey@refractions.net</a><br>
>>>> <mailto:<a href="mailto:pramsey@refractions.net">
pramsey@refractions.net</a>>> wrote:<br>
>>>><br>
>>>> This wouldn't be in vanilla arcview,
was it in Network Analyst?<br>
>>>> The top<br>
>>>> 80% of points by drive distance might
yield this shape. Finding <br>
>>>> the<br>
>>>> points would be straightforward, and
then the hull building<br>
>>>> would be the<br>
>>>> hand-waving part.<br>
>>>><br>
>>>> P <br>
>>>><br>
>>>> William Andersen wrote:<br>
>>>> > Paul, Steve,<br>
>>>> ><br>
>>>> > Thanks for the quick
replies, unfortunately it's pretty hard <br>
>>>> to tell<br>
>>>> > from those images if
they match.<br>
>>>> ><br>
>>>> > I've done some more
digging and it turns out that these<br>
>>>> shapes were <br>
>>>> > created in Arcview
3.x. The notes I have say...<br>
>>>> ><br>
>>>> > > This
approach selects a number of the outliers and joins the<br>
>>>> extreme <br>
>>>> > points using
elliptical arcs.<br>
>>>> > > The
arcs are all created in a direction moving out from the<br>
>>>> store.<br>
>>>> ><br>
>>>> > However, I dont see
customer points at the discontinuities in<br>
>>>> the<br>
>>>> hulls,<br>
>>>> > so it appears that the
"extreme points" are perhaps <br>
>>>> interpolated.<br>
>>>> ><br>
>>>> ><br>
>>>> > Will<br>
>>>> ><br>
>>>> > On 7/5/06, *Paul
Ramsey* < <a href="mailto:pramsey@refractions.net">pramsey@refractions.net</a><br>
>>>> <mailto:<a
href="mailto:pramsey@refractions.net">pramsey@refractions.net</a>><br>
>>>> > <mailto:<a
href="mailto:pramsey@refractions.net">pramsey@refractions.net </a><br>
>>>> <mailto:<a
href="mailto:pramsey@refractions.net">pramsey@refractions.net</a>>>>
wrote:<br>
>>>> ><br>
>>>> >
William,<br>
>>>> > <br>
>>>> >
It doesn't look like this is a standard algorithm, but more<br>
>>>> likely a<br>
>>>> >
particular empirical technique provided by the particular<br>
>>>> software you<br>
>>>> >
were using. So substituting some other technique might<br>
>>>> yield a<br>
>>>> >
different shape entirely... do any of the techniques <br>
>>>> mentioned here<br>
>>>> ><br>
>>>> <<a
href="http://www.geospatial-online.com/geospatialsolutions/article/articleDetail.jsp?id=1348">http://www.geospatial-online.com/geospatialsolutions/article/articleDetail.jsp?id=1348
</a><br>
>>>><br>
>>>> >
<<br>
>>>><br>
>>>> <a
href="http://www.geospatial-online.com/geospatialsolutions/article/articleDetail.jsp?id=1348">http://www.geospatial-online.com/geospatialsolutions/article/articleDetail.jsp?id=1348
</a>>><br>
>>>><br>
>>>> >
sound like what was done to your data?<br>
>>>> ><br>
>>>> >
Paul<br>
>>>> ><br>
>>>> >
William Andersen wrote: <br>
>>>> > ><br>
>>>> > >
I'm fairly new to postgis, and working to automate a<br>
>>>> number of<br>
>>>> > >
processes.<br>
>>>> > >
<br>
>>>> > >
We are trying to compute market area polygons that look<br>
>>>> like the<br>
>>>> > >
attached image. These were created by some older<br>
>>>> software.<br>
>>>> > ><br>
>>>> > ><br>
>>>> > >
They are referred to as Amoeba Hulls, and they contain<br>
>>>> 80% <br>
>>>> of a<br>
>>>> > >
store's customers. However I can't find any solid<br>
>>>> documentation that<br>
>>>> > >
would allow me to reproduce them. <br>
>>>> > ><br>
>>>> > >
Does anyone have any ideas how these shapes are<br>
>>>> created or an<br>
>>>> > >
alternate name that I might be able to google? <br>
>>>> Additionally, we may<br>
>>>> > >
be in a position to finance the development of this<br>
>>>> feature.<br>
>>>> > ><br>
>>>> >
_______________________________________________ <br>
>>>> >
postgis-users mailing list<br>
>>>> >
<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>>>> <mailto: <a
href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>><br>
>>>> >
<mailto:<a href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net
</a><br>
>>>> <mailto:<a
href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>>><br>
>>>> ><br>
>>>> <a
href="http://postgis.refractions.net/mailman/listinfo/postgis-users">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
>>>> ><br>
>>>> ><br>
>>>> ><br>
>>>> ><br>
>>>><br>
>>>>
------------------------------------------------------------------------ <br>
>>>><br>
>>>> ><br>
>>>> > _______________________________________________<br>
>>>> > postgis-users mailing
list<br>
>>>> > <a
href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a><br>
>>>> <mailto:<a
href="mailto:postgis-users@postgis.refractions.net">postgis-users@postgis.refractions.net</a>><br>
>>>> > <a
href="http://postgis.refractions.net/mailman/listinfo/postgis-users">http://postgis.refractions.net/mailman/listinfo/postgis-users</a><br>
>>>><br>
>>>> _______________________________________________<br>
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