Fair enough 
Just to complete the picture, I think what is needed is what FME
provides with its option "Preserve Shared Boundaries":
http://docs.safe.com/fme/2009/html/Transformers/content/transformers/generalizer.htm
This seems to be an additional feature beyond the standard algorithms
- would be nice to know how its achieved, and especially if there are
open source implementations of this feature.
k
···
On Fri, May 21, 2010 at 3:04 PM, Bob Jolliffe <bobjolliffe@gmail.com> wrote:
On 21 May 2010 13:58, Knut Staring <knutst@gmail.com> wrote:
On Fri, May 21, 2010 at 2:35 PM, Bob Jolliffe <bobjolliffe@gmail.com> wrote:
On 21 May 2010 13:30, Knut Staring <knutst@gmail.com> wrote:
On Fri, May 21, 2010 at 2:25 PM, Bob Jolliffe <bobjolliffe@gmail.com> wrote:
Generating an orgunit hierarchy in dxf is relatively straightforward.
As long as you have some kind of parent id reference to work with.I am not sure of the algorithm to use for the simplification part but
I guess it must be pretty standard? You are just reducing the number
of points on a polygon right? My rusty maths could probably figure
out an algorithm but this has got to already exist. Does anyone have
any pointers?Yes - there is Douglas-Peucker, Visvalingam and Special Visvalingam,
you can test them at the following link. But some of these create
cracks between polygons.
http://mapshaper.com/test/demo.htmlOk. This an online shaper. Can't see any code to download
I
guess the three names above are the algorithms? Any idea what the
cracks are about? Faulty algorithm, faulty implementation of
algorithm or faulty shapefiles to start with. Might be the shapefiles
need to be pre-processed (cleaned) before transforming.Not quite sure, maybe it is linked to polygons not really sharing
borders, just overlapping, and then Switzerland's border with Germany
gets simplified differently from Germany's border with Switzerland.
Though I could be completely wrong - and it may also depend a lot on
the parameters one chooses. But it seems that the commercial tools
like FME and ArcToolbox may handle it better, or maybe the data was
just clearner, or that the tools do some automatic precleaning, as
opposed to the default versions of the algorithms as implemented in
the online Mapshaper and also in PostGIS (see below link) don't quite
preserve common borders between polygons.If there is some reasonable java code to do this, then
I would create a java class to do it somewhere in dhis and make that
class available as a an extension to the xalan xslt processor. That
sounds complicated but its not really. I did something similar with
calculating dates off excel's (dodgy) date representation.I think this is interesting, as it would potentially allow people to
upload their own shapefiles without worrying about simplification and
conversion to GeoJSON. What will also be needed is a matching
algorithm - though Jan Henrik has already implemented identical
matching and manual visual matching in the client.By the way, in addition to simplification, there is "smoothing". Most
of this is available as part of the Java Topology Suite:
http://www.vividsolutions.com/jts/jtshome.htm
http://lists.refractions.net/pipermail/jump-users/2005-July/002564.htmlYes well if someone else can provide the simplification/smoothing or
what have you I can make sure its available to the input transform.
Other than that I'm a bit out of my depth with these processes at the
moment.