[Geoserver-users] Polygon's crossing the 180 line. Has anyone got a successful recipe?

GeoServer GeoServer User
1

My usual experience with polygons that cross the 180 line, is that on rendering, the polygon gets split on 180 with ugly line down the 180. Data source is arcSDE. I am unsure whether the problem originates with the store (ie arcSDE) or within geoserver. Polygons are rendered correctly across other tile boundaries, but not this one. With line geometries we have some success by generating the geometry offset (entirely on one side of the 180) , and then shifting into correct position, but doesnt work for polygons.

Does anyone have polygons rendering properly, and if so, how are you doing it? (what data store, what extents/projection, how created).

Thanks

Notice: This email and any attachments are confidential.
If received in error please destroy and immediately notify us.
Do not copy or disclose the contents.

2

Hi Phil,

I discussed this with EPSG some years back - with respect to a coordinate system which replicated EPSG:4326 in a 0-360 longitude space (which I think would solve the ongoing 180 issues). They said that EPSG:4326 supported ±180 as well as 0-360 so there was no need for a new code, which I thought then, & still do, was a bit shortsighted - even if technically correct.

While ESRI can accept 0-360 data as EPSG:4326, any coordinate reprojection will always generate values in a ±180 space - a flag to specify which you want & convert accordingly is not available.

We have funded solutions in gdal & Postgis which work for points, & for lines & polygons which are not intersecting the 180 meridian, but have no solutions for such features which do. I have done this for some datasets, but it involves splitting & joining features as you note. This is non-trivial in the data as doing this changes feature ID’s - and I’m not aware of any rendering solution that successfly splits or joins the polygons on the fly. (Though you can “join” polygons that are split by plotting with no border, so the two parts appear as one).
The topological changes as well as reprojection is rquired. The geography datatype in Postgis is one step forward.

If you are looking for a collaborator & possible funder to support initiatives to address this in the OSGEO space, I’m there!!

Cheers,

Brent Wood

From: Phil Scadden <p.scadden@anonymised.com389…>
To: geoserver users geoserver-users@lists.sourceforge.net; geotools-gt2-users@lists.sourceforge.net
Sent: Thursday, February 13, 2014 9:41 AM
Subject: [Geoserver-users] Polygon’s crossing the 180 line. Has anyone got a successful recipe?

My usual experience with polygons that cross the 180 line, is that on
rendering, the polygon gets split on 180 with ugly line down the 180.
Data source is arcSDE. I am unsure whether the problem originates with
the store (ie arcSDE) or within geoserver. Polygons are rendered
correctly across other tile boundaries, but not this one. With line
geometries we have some success by generating the geometry offset
(entirely on one side of the 180) , and then shifting into correct
position, but doesnt work for polygons.

Does anyone have polygons rendering properly, and if so, how are you
doing it? (what data store, what extents/projection, how created).

Thanks

Notice: This email and any attachments are confidential.
If received in error please destroy and immediately notify us.
Do not copy or disclose the contents.

Android apps run on BlackBerry 10
Introducing the new BlackBerry 10.2.1 Runtime for Android apps.
Now with support for Jelly Bean, Bluetooth, Mapview and more.
Get your Android app in front of a whole new audience. Start now.
http://pubads.g.doubleclick.net/gampad/clk?id=124407151&iu=/4140/ostg.clktrk

Geoserver-users mailing list
Geoserver-users@anonymised.coms.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/geoserver-users

3

I discussed this with EPSG some years back - with respect to a coordinate system which replicated EPSG:4326 in a 0-360 longitude space (which I think would solve the ongoing 180 issues). They said that EPSG:4326 supported ±180 as well as 0-360 so there was no need for a new code, which I thought then, & still do, was a bit shortsighted - even if technically correct.

Which explains why the build-it-offset-and-shift works okay. (The coords are then in 0-360 space).

While ESRI can accept 0-360 data as EPSG:4326, any coordinate reprojection will always generate values in a ±180 space - a flag to specify which you want & convert accordingly is not available.

The odd thing is that the polygon in not split in the data store. However, the moment you try to render on a different projection in Arcmap or geoserver, then the polygon shows up as split.

I have postgis as an option (not ideal). When you are requesting tiles, polygons are rendered fine across tile boundaries so I dont understand why this is so hard on the 180 if you have geometry stored in 0-360 (or the projected equivalent).

(Though you can “join” polygons that are split by plotting with no border, so the two parts appear as one).

A thought but limits the kind of fill too.

If you are looking for a collaborator & possible funder to support initiatives to address this in the OSGEO space, I’m there!!

If we can find someone interested, then I would certainly try to help with the funding.

Notice: This email and any attachments are confidential. If received in error please destroy and immediately notify us. Do not copy or disclose the contents.

4

On Thu, Feb 13, 2014 at 11:59 PM, Phil Scadden <p.scadden@anonymised.com> wrote:

While ESRI can accept 0-360 data as EPSG:4326, any coordinate reprojection
will always generate values in a +-180 space - a flag to specify which you
want & convert accordingly is not available.

The odd thing is that the polygon in not split in the data store. However,
the moment you try to render on a different projection in Arcmap or
geoserver, then the polygon shows up as split.

In a different projection. Can you make an example?

Cheers
Andrea

--
== Our support, Your Success! Visit http://opensdi.geo-solutions.it for
more information ==

Ing. Andrea Aime
@geowolf
Technical Lead

GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054 Massarosa (LU)
Italy
phone: +39 0584 962313
fax: +39 0584 1660272
mob: +39 339 8844549

http://www.geo-solutions.it
http://twitter.com/geosolutions_it

-------------------------------------------------------