[mapserver-users] Creating an abutter's list (was: Accessing Vertices of a Shape - PHP MapScript)

[Richard Greenwood]

I've used a buffered polygon to select adjoining polygons in 
non-topological GIS software with good success. One quick way to 
approximate a buffer would be to scale the source polygon around its 
centroid by a small factor, such as 1.1. I'm not that hot of a PHP 
programmer to offer you the code in PHP, but the basic polygon scaling 
algorithm is to walk the vertex list and calculate the vector from the 
centroid to the vertex, then created the new scaled vertex from the 
vector_length *  scale_factor. Or maybe just add a fixed amount to the 
length of the vector.

Rich

At 10:19 AM 11/19/2002 -0500, you wrote:
>Kevin Flanders wrote:
> >
> > Is there a way of exploiting this functionality to create an abutter's list
> > function for municipal applications?  If we can create a new shape that
> > mimics an existing/selected parcel, then can't we use that shape like we
> > would a user-defined query rectangle to intersect parcel features?
> >
> > I know there has been talk about abutters list before, but it doesn't seem
> > like there has been any resolution....
> >
>
>
>If I understand well, the idea is to select all parcels that are
>adjacent to a selected parcel.  It may not be possible to use
>QueryByShape for this because it looks for shapes that intersect or are
>located inside the shape you use for the query... so non-intersecting
>neighbors won't be selected.
>
>The best would be if we could create a new shape that is the parcel of
>interest with a buffer added around it and use that buffered parcel in a
>queryByShape().  Unfortunately for you there is no way to create such a
>vector buffer in MapServer.
>
>Another trick could be to sample points every few meters along the
>border of the parcel of interest and do a point query at every step with
>a tolerance of half the distance between the sampled points.  You would
>compile a list of the returned parcel ids as you walk around the parcel
>and this would give you your list of abutters.
>
>I'll CC: to the list where others may have better suggestions.
>
>Daniel
>--
>------------------------------------------------------------
>  Daniel Morissette               morissette at dmsolutions.ca
>  DM Solutions Group              http://www.dmsolutions.ca/
>------------------------------------------------------------


Richard W. Greenwood, PLS
Greenwood Mapping, Inc.
Rich at GreenwoodMap.com
(307) 733-0203
http://www.GreenwoodMap.com