[georss] WAS: GeoRSS Validation Service? RETURNING TO:multiplelocations and time

Fri Mar 9 15:52:21 EST 2007

Thanks Ron-
   Coordinate encoding is indeed one of the primary differences I've seen between various gml representations of a given geometry (e.g. gml:Point). But there are others. For example, in following link Dr Reed describes 2 different ways to define a polygon:

http://www.oasis-open.org/archives/emergency-gis/200507/msg00003.html

The coordinate encoding is identical in these 2 examples. I don't think this variation is attributable to spec differences.

It would be nice to come up with a running list of gml examples that cover all of the variations of gml geometries across all 3(?) versions of the gml spec. Perhaps there's one out there already - I just haven't seen one yet. I'd love to expand the list I have so far to include additional gml geometries, 3d geometries, and gml time stamps (e.g. a GML point that's represented using x,y,z,t). Would you be willing to help compile such a document?

By the way, I believe the code I posted earlier covers all of the coordinate encoding schemes the OGC has come up with so far. However, as stated on the download page, it only supports 2d tuples at the moment.

Thanks again,
Peter

----- Original Message ----
From: Ron Lake <rlake at galdosinc.com>
To: Peter Borissow <peter.borissow at yahoo.com>; Raj Singh <raj at rajsingh.org>
Cc: Allan Doyle <adoyle at eogeo.org>; georss at lists.eogeo.org
Sent: Friday, March 9, 2007 3:22:44 PM
Subject: RE: [georss] WAS: GeoRSS Validation Service? RETURNING TO:multiplelocations and time

Hi,

Let me address the issue of coordinate encoding which I think is what
you are referring to by GML variations.

The original GML encoding (v1.0, V2.1.2) used <gml:coordinates> on
Points, LineStrings etc.  This was string valued with attributes that
could be used to specify coordinate and n-tuple separators. Defaults
were comma and whitespace respectively. This is the same as used in KML.
There was another variant that used explicit x,y tags but this was
fortunately deprecated and then deleted.

GML v3.1.1 introduced the use of not string values but XML token lists
so that an additional string parser was not required, and so that all
coordinate values were visible in XML.  This required the introduction
of <gml:pos> and <gml:posList> elements.  This is also somewhat more
compact than is the case for the deprecated coordinates.

Note that <gml:coordinates> is dropped (the XML content model will still
exist) in GML v3.2 so only pos and posList will be supported.

I hope that this helps.

R

-----Original Message-----
From: Peter Borissow [mailto:peter.borissow at yahoo.com] 
Sent: March 9, 2007 11:41 AM
To: Ron Lake; Raj Singh
Cc: Allan Doyle; georss at lists.eogeo.org
Subject: Re: [georss] WAS: GeoRSS Validation Service? RETURNING
TO:multiplelocations and time

I believe I used the term "variations". I'm by no means an expert on gml
- I haven't spent the time to actually understand the differences
between the differest versions. All I know is what I've seen - and what
I've seen is a lot of different ways to express a point, line, polygon,
etc. Perhaps these differences are a result of different versions of the
spec - I just don't know.

What I've tried to do in the atom feed is capture some of the different
ways people describe a geometry using gml. I'd love to create a complete
set of examples for all the different flavors of gml - something people
can use to test thier parsers. I guess it's possible to automatically
generate these examples using schemas - I just haven't spent the time to
do something like that. In the meantime, I've employed a rather lazy
approach - I've simply been grabbing examples off the web.

Does that answer your question? 

Thanks,
Peter

----- Original Message ----
From: Ron Lake <rlake at galdosinc.com>
To: Peter Borissow <peter.borissow at yahoo.com>; Raj Singh
<raj at rajsingh.org>
Cc: Allan Doyle <adoyle at eogeo.org>; georss at lists.eogeo.org
Sent: Friday, March 9, 2007 2:14:17 PM
Subject: RE: [georss] WAS: GeoRSS Validation Service? RETURNING
TO:multiplelocations and time

Hi Peter:

What do you mean by variations of GML?  Do you mean different versions
(2.1.2, 3.1.1)?  Otherwise I don't understand what you mean?

Ron

-----Original Message-----
From: georss-bounces at lists.eogeo.org
[mailto:georss-bounces at lists.eogeo.org] On Behalf Of Peter Borissow
Sent: March 9, 2007 10:01 AM
To: Peter Borissow; Raj Singh
Cc: Allan Doyle; georss at lists.eogeo.org
Subject: Re: [georss] WAS: GeoRSS Validation Service? RETURNING
TO:multiplelocations and time

Well I finally got a chance to knock out some code this morning - a java
library to parse GeoRSS.

You can download it here:

http://www.kartographia.com/geoRSS/

Again, my hope is that we can start generating and sharing some
reference software to parse GeoRSS.

I haven't had a lot of time to test this library. I can definately use
some additional test data if you have any to share. I've created an atom
feed to try to capture all of the variations of GML - even those not yet
supported by GeoRSS.

http://www.kartographia.com/geoRSS/examples/Atom.xml

My hope is that once we have some reference software, we can start
introducing more complex GML - like multipoint!

Thanks,
Peter

----- Original Message ----
From: Peter Borissow <peter.borissow at yahoo.com>
To: Raj Singh <raj at rajsingh.org>
Cc: Pat Cappelaere <pat at cappelaere.com>; Allan Doyle <adoyle at eogeo.org>;
georss at lists.eogeo.org
Sent: Friday, March 2, 2007 5:13:53 PM
Subject: Re: [georss] WAS: GeoRSS Validation Service? RETURNING TO:
multiplelocations and time

So that's a good point - the existing GeoRSS "spec" provides the option
to specify coordinates in ANY reference frame! And you think multipoint
geometries are going to scare users?

Just kidding. 

Anyway I'll try to get a partial implementation of a java-based GeoRSS
parser out sometime this weekend or early next week for you to review. I
already wrote one a while back - I just need to clean it up. It supports
the following features:

- RSS, Atom, and RDF
- GeoRSS "Simple" Geometries
- A subset of GML Geometries (Point, Line, Polygon, MultiPoint,
MultiLine, MultiPolygon, Envelope)
- Supports the 3 different GML coordinate formats
- It also happens to support DB2 and Sybase/SQS geometry types but I'll
cut that code out

All the code does is "normalize" the geometries into a set of points and
extracts the srs attribute. Coordinate transformation, rendering,
mensuration, etc. are all higher level functions that should be handled
by other classes. 

So why do I feel the need to do this? Because I'm still trying to
convince you to adopt a wider range of gml geometries into the GeoRSS
spec. 

Have a good weekend.

Peter

----- Original Message ----
From: Raj Singh <raj at rajsingh.org>
To: Peter Borissow <peter.borissow at yahoo.com>
Cc: Pat Cappelaere <pat at cappelaere.com>; Allan Doyle <adoyle at eogeo.org>;
georss at lists.eogeo.org
Sent: Friday, March 2, 2007 3:57:55 PM
Subject: Re: [georss] WAS: GeoRSS Validation Service? RETURNING TO:
multiplelocations and time

Parsing is one thing. Doing something smart with it is another. For  
example, if you get a GeoRSS GML geometry in, for example, a state  
plane coordinate system, can you either:
a. reproject it into lat/long to show on a Google/Yahoo/MS map or
b. reproject your map into the state plane system

That's just one example of the more general point that if you support  
GeoRSS GML, you should be able to manipulate coordinate reference  
systems in your application.
---
Raj

On Mar 2, 2007, at 2:53 PM, Peter Borissow wrote:

> Parsing RSS and Atom is a joke. Parsing GML geometries is not that  
> complicated either. In fact I wrote a limited GML parser that can  
> handle points, lines, and polygons + their "multi-" varients in  
> less than an hour. Adding the GeoRSS "simple" geometries took even  
> less time.

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