________________________________
De: Alexandre Barboza
Enviado: segunda-feira, 23 de outubro de 2017 14:29
Para: Ian Turton
Assunto: RE: [Geoserver-users] Buffer error
Hi Ian!
Thanks again for the quick reply!
We think about its answer. When we publish the Layer using EPSG 4326, the
buffer results are being distorted when we measure it, our data is between
latitudes -22 and -23.
Does QGIS use some algorithm to compensate this distortion? This data
distortion does not occur in the QGIS or other Gis software.
Are any way to apply the same algorithm, if exist, used on QGIS on geoserver?
best regards!
________________________________
De: Ian Turton <ijtur...@gmail.com>
Enviado: segunda-feira, 23 de outubro de 2017 13:47
Para: Alexandre Barboza
Cc: geoserver-users@lists.sourceforge.net
Assunto: Re: [Geoserver-users] Buffer error
Then your map is distorted, Google maps uses EPSG:3587 (or epsg:900913 if you
are using old terms) and that is a web Mercator projection which has an
increasing E-W distortion as you move away from the equator. The other possible
issue is that depending on how you projected your point into a local CRS and
then projected the buffer back to WGS there is a chance to introduce
inaccuracies into the process. Unless you just guessed a degrees to metres
conversion factor that seemed about right for one of your points?
Anyway, on that map circular buffers should look stretched out like yours do.
Ian
On 23 October 2017 at 16:26, Alexandre Barboza
<ambarb...@hotmail.com<mailto:ambarb...@hotmail.com>> wrote:
Hi Ian
Thanks for your answer!
We are using EPSG 4326 projection, and display it on Google Maps API, always
tiled. When we open it on QGIS the buffer size dos not is the same that we
specified on X axis and Y axis. sample: when we do a buffer of 500 meters
(radius) the x axis result about 450 meters and Y axis have 500 meters.
On this url
http://www.ide.emplasa.sp.gov.br/geoserver/emplasa/TESTE_BUFFER_GEOWGS84/wms?
we did a buffer with distance of 500 meters using EPSG 4326 layer
On our website the buffer url is
http://www.ide.emplasa.sp.gov.br/geoserver/emplasa/LOCALIDADES_EMPLASA_SAUDE/wms?styles=SYS_SIMM_ESTILO_BUFFER_DINAMICO_THE_GEOM&env=polygonStrokecolor:003300;polygonFillcolor:FF0000;bufferSize:500&CQL_FILTER=NOME_MUNIC%20LIKE%20%27Diadema%27&service=WMS&version=1.1.1&request=GetMap&layers=emplasa:LOCALIDADES_EMPLASA_SAUDE&format=image/png&tiled=false&TRANSPARENT=true&srs=EPSG:900913&bbox=-5190379.968676608,-2727273.1692150906,-5187933.9837714825,-2724827.184309963&width=256&height=256
________________________________
De: Ian Turton <ijtur...@gmail.com<mailto:ijtur...@gmail.com>>
Enviado: segunda-feira, 23 de outubro de 2017 12:49
Para: Alexandre Barboza
Cc:
geoserver-users@lists.sourceforge.net<mailto:geoserver-users@lists.sourceforge.net>
Assunto: Re: [Geoserver-users] Buffer error
TBH that looks like a projected (EPSG:3857) map to me, so I would expect some
distortion. You probably don't want to use tiles for that layer either, or
maybe experiment with gutters to see if that helps with the edge cases.
Please show the actual request to the buffer process so we can test it and see
if there is any distortion when there is no projection.
Ian
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