I've had quick look at the maths and the basics are rather easy at first
glance,
if anyone fancies programming it before i do they are quite welcome. But i
won't be
using MapBasic.
take coordinate list of bounding polygon,
for each pt.x find pt.x-1 & pt.x+1.
calculate internal angle A by the following,
c is the distance between pt.x-1 and pt.x
b is the distance between pt.x+1 and pt.x
a the distance between pt.x-1 and pt.x+1.
A = cos-1 ((b*b + c*c + a*a)/2ba)
calculate bearing from pt.x to pt.x+1
add internal angle A to bearing
add (360 degs. - A)/2 angle to result
determine buffer's coorinate using pt.x coordinates, bearing and distance.
I fancy there might be some tuning in the regard of identifying internal
angles.
regards,
Andy Bailey
----- Original Message -----
From: "PPR Jon Bloor" <[EMAIL PROTECTED]>
To: "Mapinfo User Group" <[EMAIL PROTECTED]>
Sent: Tuesday, March 28, 2000 12:34 PM
Subject: Re: MI Date: Tue, 28 Mar 2000 09:37:53 +0100
> Dear Andy and all other listers
>
> I would like to ask... Why does Mapinfo carry out circular buffering.
> Quite often I want to create a catchment area based on a certain
> boundary plus 0.5 km for example. Often my initial polygon is quite
> complex, but the resultant buffer is always a rather poor approximation
> (despite using a range of segments per circle).
>
> I am sure (if memory serves me right) Arc/Info does the job much more
> accurately!
>
> Curious in Anticipation
>
> Jon Bloor
>
>
>
> Andy wrote:
>
> > Do you know of any good web sites covering
> > computational geometry / GIS algorithms. I am
> > interested in polygon/polygon intersection and
> > buffering but not circular buffering i.e. if you have
> > a polygon I need an algorithm that creates a buffer of
> > equal size all round the polygon so that the buffer
> > mimicks the shape of the polygon. regards,andrew bailey
>
>
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