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#1
benbakelaar

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I'm currently researching this, but if anyone knows how in ArcGIS off the top of your head. I have a data set with points, each of which is associated with one of 7 "networks". I want to make a coverage (overlay polygon - bounding box) for each of the networks, to show its spatial extent on the ground.

EDIT 1:
Apparently the correct name for this is a "convex hull".
http://support.esri....erm=convex hull

EDIT 2:
Got this to work...
http://arcscripts.es....asp?dbid=12084
But it required some VBA editing. Any easier solutions?

#2
benbakelaar

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My next question is, how do I produce a nice curvy coverage based on the jaggy pointy convex hull polygon?

#3
Matthew Hampton

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There's always the "export-to-Illustrator-and-simplify-the-path" answer, but that would be too easy.

There must be some complex way Arc can do it. ESRI does have a new "generalize" function on their advanced-editing toolbar...I am sure there are other solutions also.

Are you using Network Analyst?

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#4
benbakelaar

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There's always the "export-to-Illustrator-and-simplify-the-path" answer, but that would be too easy.

There must be some complex way Arc can do it.  ESRI does have a new "generalize" function on their advanced-editing toolbar...I am sure there are other solutions also. 

Are you using Network Analyst?

<{POST_SNAPBACK}>


I haven't tried Network Analyst yet, maybe I will take a look. I did find the tools I needed in XTools 4.0. But it's still quite complicated... I have to export the convex hull polygon to a polyline, then simplify the polyline, and then convert the polyline back to a polygon in order to get a fill.

Basically, I just want to turn every vertex into a bezier curve instead of a straight line, especially because my convex hull is bounded in some cases by only 5 points, so generalizing wouldn't really help much.

#5
paul

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Check out Hawths Tools (free extension).

http://www.spatialec...s/createmcp.php

#6
david17tym

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et geowizards (www.ian-ko.com) have simple tools available in arcview to:

1. generate polylines from points
2. smooth result with bezier curves
3. build polygons from polylines

the evaluation vesion limits processing to datasets with < 100 features, the full unlimited version is around ?100.

hope this helps,

dave

#7
pghardy

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My next question is, how do I produce a nice curvy coverage based on the jaggy pointy convex hull polygon?

<{POST_SNAPBACK}>

It doesn't help you in the short term, but we do know here at ESRI that "Smooth Polygon" and "Aggregate Points to Polygon" are both tools that would be useful additions to the set of geoprocessing tools, and are in the wish list for future development (competing for development resources against all the other facilities that people wish for!).

At ArcGIS 9.2, we added several tools for generalization, including "Simplify Polygon" to go alongside the previously available "Simplify Line". There was already a "Smooth Line" tool, but we haven't yet done the corresponding "Smooth Polygon" (it's harder than you might think to deal with the complexities of shared polygon boundaries).

Similarly, we have an "Aggregate Polygons" tool, but we don't yet have an "Aggregate Points to Polygons" tool. I'll record this thread as a piece of supporting evidence and use case for the requirement.

Note that there are often practical ways of achieving results for particular datasets using combinations of existing tools - e.g. for your convex hull polygons, you could use "Feature to Line", then "Smooth Line", then "Line to Polygon" tools.
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Paul Hardy
ESRI Europe (phardy@esri.com)

#8
benbakelaar

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Everyone, thanks for your replies! As some of you have suggested, I have indeed been doing a 3-step conversion process. Luckily I was only working with 10 discrete polygons.

pghardy, believe me I don't think it could ever be simple to smooth out shared polygon boundaries :) As I mention above, I was working wtih discrete polygons, and I am excited to hear about the new features in ArcGIS 9.2. I would suggest though if your coder/engineers can't tackle "Smooth Polygon" with shared boundaries, at least they could do Smooth Polygon with discrete boundaries. Or even just offer a chained tool that runs all three steps that you mention in one process.

#9
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he he, shared polygon boundaries are not a problem in ArcInfo workstation (since the coverage data model maintains topology very strictly), too bad that the generalization functionality is not super cool...
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#10
natcase

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My next question is, how do I produce a nice curvy coverage based on the jaggy pointy convex hull polygon?

<{POST_SNAPBACK}>


Do the networks in question actually have hard edges to their territories? Might it make sense to create soft edged shapes using photoshop functions to spread and feather? It makes me graphically nervous to imply delineated territories where none actually are in place.

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#11
benbakelaar

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Do the networks in question actually have hard edges to their territories? Might it make sense to create soft edged shapes using photoshop functions to spread and feather? It makes me graphically nervous to imply delineated territories where none actually are in place.

<{POST_SNAPBACK}>


Well you are completely right, the delineations are graphical only, but this is the case even with the hard-edged convex hull. In my specific case, these are emergency feeding program "collectives" which share information/resources in their immediate area, for instance, all EFP sites in a "neighborhood". In the end, we decided to leave the map displaying point data, color-coded by network. :)




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