[mapserver-users] Buffer features?

Thu Feb 17 06:08:20 PST 2011

Thank you everyone!  

I've got something that basically is working now.  One other thing I was
curious about, with regard to a multi-ring buffer, is isolating results
within one buffer range (for example, 0-50 meters, then 50-100 meters).
Using a simple buffer shape will give me results for all rings, 0 to
(d).  I have some ideas on addressing this, basically comparing results
from one range to another and eliminating duplicates.  But if somebody
has a better idea, I'd love to hear it.

________________________________

From: Lime, Steve D (DNR) [mailto:Steve.Lime at state.mn.us] 
Sent: Tuesday, February 15, 2011 3:59 PM
To: Bistrais, Bob
Cc: mapserver-users
Subject: RE: [mapserver-users] Buffer features?

MapServer queries, at least some of them, respect layer tolerances which
effectively acts like a buffer. You can also take the result of your

buffering operation and use it in a queryByShape() operation. Make sure
you set your layer tolerances appropriately (probably to 0) so that

you get features that intersect with the shape.

Steve

From: mapserver-users-bounces at lists.osgeo.org
[mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Bistrais,
Bob
Sent: Tuesday, February 15, 2011 1:54 PM
To: Lime, Steve D (DNR)
Cc: mapserver-users
Subject: RE: [mapserver-users] Buffer features?

OK, that makes sense.  One more thing I'm not clear on- I can draw my
buffer around the selected feature.  How can this buffer now be used to
query another layer?  I guess it's similar to other queries, but how to
select this buffer feature and use it as the input to the query?

________________________________

From: Lime, Steve D (DNR) [mailto:Steve.Lime at state.mn.us] 
Sent: Tuesday, February 15, 2011 1:43 PM
To: Bistrais, Bob
Cc: mapserver-users
Subject: RE: [mapserver-users] Buffer features?

You'd need to use 3 different layers and change your code to create 3
different buffered shapes accordingly.

Steve

From: mapserver-users-bounces at lists.osgeo.org
[mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Bistrais,
Bob
Sent: Tuesday, February 15, 2011 12:30 PM
To: Lime, Steve D (DNR)
Cc: mapserver-users
Subject: RE: [mapserver-users] Buffer features?

Not to make life more difficult, but is it possible to create a
multi-ring buffer, basically 3 polygons at 3 different distances from a
selected feature?

________________________________

From: Lime, Steve D (DNR) [mailto:Steve.Lime at state.mn.us] 
Sent: Tuesday, February 15, 2011 12:22 PM
To: Tamas Szekeres
Cc: mapserver-users
Subject: RE: [mapserver-users] Buffer features?

Not quite, I'm thinking of a single layer setup:

LAYER

   DATA myfile.shp # or whatever connection information is necessary

  TYPE POLYGON

   STATUS DEFAULT   

   NAME 'buffered_shapes'

   GEOMTRANSFORM (buffer([shape], 500))  # buffer each shape by 500 map
units

   # classes and styles follow

   TEMPLATE 'void'

END

The GEOMTRANSFORM would be applied as shapes are pulled from a data
source so you would draw or, potentially, query the transformed shapes.
The difference between a layer-level GEOMTRANSFORM and a style-level one
is the coordinates they operate on. Layer-level work would be done on a
raw feature in map coordinates and style-level works on pixels. We do
layer-level stuff already, conceptually, in the form of projections and
clipping. The GEOMTRANSFORM just provides a way of extending that
work...

Note this type of GEOMTRANSFORM expression is working for buffers in
STYLEs in trunk (but using pixels for the moment).

Steve

From: Tamas Szekeres [mailto:szekerest at gmail.com] 
Sent: Tuesday, February 15, 2011 11:12 AM
To: Lime, Steve D (DNR)
Cc: mapserver-users
Subject: Re: [mapserver-users] Buffer features?

Steve,

Did you mean to achieve something like?:

LAYER
     CONNECTIONTYPE TRANSFORM
     CONNECTION sourcelayer  # reference to another layer
     NAME transformlayer
     PROCESSING "TRANSFORM=(buffer([shape]))"
     TEMPLATE query.html
     ....
END
LAYER
     CONNECTIONTYPE SHAPE
     DATA myfile.shp
     NAME sourcelayer
     ....
END

Which is simple and easy to implement.

Best regards,

Tamas

2011/2/15 Lime, Steve D (DNR) <Steve.Lime at state.mn.us>

I'd approach RFC 22, especially the transform piece, differently now
with the parser changes  implemented in 6.0. We now have (with GEOS
enabled) an expression syntax available to support things like
buffering, convex hull, differences, etc... or combinations thereof. I'd
implement layer-level GEOMTRANSFORMs in that case using these
expressions.

On the query result side of things I'd consider adding a layer template
as a layer option. This would kinda work like the approach outlined for
Bob. You'd define a presentation template layer (no DATA value) and run
the query results through it instead of the regular layer (for certain
querymap types, e.g. highlight).

Steve

From: mapserver-users-bounces at lists.osgeo.org
[mailto:mapserver-users-bounces at lists.osgeo.org] On Behalf Of Tamas
Szekeres
Sent: Tuesday, February 15, 2011 3:06 AM
To: Bistrais, Bob
Cc: mapserver-users
Subject: Re: [mapserver-users] Buffer features?

In accordance with the problem mentioned, I recall a resonable
enhancement as described in RFC22a
<http://www.mapserver.org/development/rfc/ms-rfc-22a.html>  which would
provide an option to configure all the stuff in the mapfile (not
requiring MapScript) and would make it easier to customize the query
maps as well.

With this enhancement 2 new layer data providers could be implemented,
like:

1. CONNECTIONTYPE=QUERYRESULT would provide to represent the result sets
of one layer in a new layer.
2. CONNECTIONTYPE=TRANSFORM would provide simple geometry
transformations on a source layer and then provide the modified features
as a new layer.

By chaining these layers together in a map configuration we could get
such results
<http://trac.osgeo.org/mapserver/attachment/ticket/2128/sample4.png>  as
included in the RFC document.

I consider this kind of enhancement could be implemented within the
scope of 1-2 days of work (comparable with a fully elaborated MapScript
solution providing the same)

Best regards,

Tamas

2011/2/14 Bistrais, Bob <Bob.Bistrais at maine.gov>

This question may have come up before, but I haven't found it in the
archives.  I would like to take a selected feature and buffer it to a
specified distance.  I know it's possible to do a queryByPoint with a
buffer distance, but I need to create an actual buffer shape to display
on the map.  Has anyone done something like this before?  Does MapServer
have this capability?

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