Martin,
I have done a lot of development in CAD/CAM and I think I would take the
machining approach to the offset problem. This would be to generate the
profile of a ball rolling a long the profile. Then you will have to
decide how to handle the end caps which really only defines where you
initially place the ball. The two logical placement positions are:
1) center the ball on an extension of the profile
------profile----------->#<--r--.
2) center the ball normal to the end of the profile
------profile----------->#
^
|
r
|
.
where # = end of the profile
r = is the ball radius
. = center of the ball
In the very narrow V case using option 2) I would think t you would get
something like:
..
. .
# #
\ /
\/
Sorry for the crude graphics but the .... lines should be shown normal
to the \ and / lines. For case 1) you would have two arcs starting on
the extensions of the \ and / lines arcing downward toward the center
and meeting at the angle bisector of \ and / if they are equal in
length, which is the degenerate case I think you were asking about.
I have not checked out any of the degenerate cases for the buffer
algorithm, but I assume you are doing the reasonable thing. In which
case, I would kind of expect that if I generated a buffer along a
profile and then extended the original profile from its ends until it
went through the buffer and then wrapped the ends around to the right or
left side to meet and form a polygon and intersected the polygon with
the buffer then I would get the same as if I had generated the buffer on
the right or left respectively.
But, this might not be what ESRI does, so it would be nice if Jing or
others with access to ESRI products could post some images of what ESRI
does if that is the use case that needs to be matched.
-Steve
Martin Davis wrote:
Yes, I know that negative buffer won't doesn't handle left/right - that
suggestion was in answer to Stephen's question about "shrinking"
buffers.
What I'm looking for is some examples of what left/right buffers look
like (especially for pathological cases such as very narrow V shapes)
Martin Davis, Senior Technical Architect
Vivid Solutions Inc. www.vividsolutions.com
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
zhangjing
Sent: May 17, 2006 6:28 PM
To: GEOS Development List
Subject: Re: RE: [geos-devel] left and right buffer
Our client need a tool like ArcToolbox Buffer which has
functionality of Left/Right/Full buffer, and i believe
negative distances could not be applied to polyline geometry.
Thanks.
Am I missing something? Isn't this the functionality that negative
buffer distances gives today?
Martin Davis, Senior Technical Architect
Vivid Solutions Inc. www.vividsolutions.com
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
Stephen Woodbridge
Sent: May 17, 2006 10:06 AM
To: GEOS Development List
Subject: Re: [geos-devel] left and right buffer
Hi Martin,
I think a useful variant of this for polygons it to be able
to specify
inside or outside, so you could effectively grow and shrink
the polygon.
The "grow" option is great for finding abutters, and I think
the buffer
command today already does this.
The "shrink" option is great for defining/showing boundary offsets
within a lot that might be needed to insure zoning rules.
-Steve
Martin Davis wrote:
I'm curious what your use case is for this
functionality. Can you
post some sample data that you want L/R buffers for, and
perhaps an
image of what you expect the results to look like?
Martin Davis, Senior Technical Architect
Vivid Solutions Inc. www.vividsolutions.com
Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of
zhangjing
Sent: May 17, 2006 12:10 AM
To: geos-devel@geos.refractions.net
Subject: [geos-devel] left and right buffer
hi,
Is there any way in GEOS to calculate geometry's left or right
buffer ?
TIA
Jing Zhang
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