GeoWeb Blog

The Need for Restful Services for Geospatial Information

pcarlos — Tue, 17 Jul 2007 22:54:55 +0000

So far the OGC has mainly interpreted Web Services in non-restful terms. While the idea of linking to remote resources has been part of GML since version 1., it has not been exploited in a restful sense in anything beyond the most simple experiments. As pointed out by Sean Gillies and others (see geo-web-rest@googlegroups.com ) rest depends on having a consistent http interface. Sean has already described this very well, so I will just quote his e-mail here:

“A uniform interface is the “core tenet” of REST:

(http://rest.blueoxen.net/cgi-bin/wiki.pl?RestInPlainEnglish)

For the Web, it is:

- GET: “give me a representation of the resource”;
- PUT: “replace the resource’s representation with this one”;
- POST: “create a new resource from this representation”;
- DELETE: “eliminate the resource”.

The closest thing WxS has to resources are the service endpoints specified by the online resource URLs. What is their HTTP interface?

- GET: “get a capabilities document, a feature collection, or some other thing depending on the values of ’service’, ‘request’, and other parameters”;
- PUT: undefined
- POST: “get a capabilities document, or a feature collection, *or* create, update, or delete features, or do almost anything depending on the values of ’service’, ‘request’, and other parameters”;
- DELETE: undefined

GET and POST are more or less interchangeable, depending on the particular implementation. What’s important to WxS are the other request arameters: “service”, “request”, “typename”, etc. WxS has *no* uniform HTTP interface, and is therefore *not* RESTful.”

So by this definition, our OGC WxS services do NOT appear to be restful. One might wonder if we could also advance toward a more restful architecture by eliminating capabilities documents – factoring these into additional interfaces?

-Ron

(Visit Sean Gillies’ Blog http://zcologia.com/news/)

Crowd Sourcing and the Role of Government in the GeoWeb

pcarlos — Mon, 16 Jul 2007 21:16:01 +0000

We have all seen that some pretty exciting technologies for sourcing geographic data are on the horizon. These appear to challenge the traditional methods for data collection and may significantly impact the role of government in this regard. Several companies have shown that road data can be acquired by so called pilot vehicles – GPS equipped cars, vans or trucks that tell us where the roads are, and the state of the traffic at the same time. Furthermore this can be done without a crew of surveyors. Similar approaches applied to photographs of public buildings submitted to sites like Flickr have been used to construct building geometry models. Again this is accomplished without surveys or other formal methods for data collection. Combined with imagery from satellites and remotely piloted vehicles, can the day be far off where government as data collector is a thing of the past?

If this is the case, what is the role of government in the GeWeb? Just another data consumer?

-Mohammed

Do we need formal standards bodies?

pcarlos — Mon, 02 Jul 2007 20:30:44 +0000

Why do we need formal standards bodies? It was only a short while ago that the idea of creating an online encyclopedia would have seemed little more that a pipe dream – now Wikipedia is an increasingly important and increasingly respected source for all kinds of information about nearly every topic on earth. Why can we not do the same thing with standards and specifications? A Specipedia or Wikispec? How is the creation of open standards different in a process sense from the creation of open source software? A Wiki, some process management tools and we are away? No?

- George

What is a Feature?

admin — Wed, 27 Jun 2007 17:19:33 +0000

We all talk these days about modern GIS being feature based - but does anyone really know what that means? Is a feature just an alias for an object? An application domain object? Do we go back to the old way of thinking where features were things one sees on the map? You mean they are not? How can someone say a coverage is a feature? An observation? Are features only discrete things like rivers, airports and shipping lanes? Vector things? What are vector things anyways? Does the old distinction of vector and raster really provide a suitable framework for talking about the world? Why raster? What does that mean?If I look out the window I am fortunate enough to see the mountains and the ocean going off into the distance. They are not lines nor points. I can think of them as continuous surfaces - elevation surfaces. At the same time, I see discrete, named things of interest like mountain peaks, ridges and cliffs - and I see these things on a map. Is ths what features are - discontunities - distinguished aspects of the otherwise continuous environment? I define a lake as polygon wih sharply defined edges - but is the water and land boundary really so well defined? What about swamps and marsh lands along the shore? How far can I push the idea of discrete features?

Features are supposed to be named application objects with a list of properties that characterize them. Sounds like an object? So a road has a width, a number of lanes, a surface type, the date it was constructed. Real simple huh? But the texture of the road is not constant along its length - heck even the number of lanes varies from one place to another. So the properties of the road must be thought of functions of the position on the road? Is this true for all features?

In the early days of GIS, many GIS were raster based. In fact there was a sort of competition for a time between vector-based and raster-based GIS. How can that be? What is a feature in a raster-based GIS? Well think of that road. It has an associated characteristic function which is like an image defined on the land surface - it is 1 when there is a road point and it is 0 when it is not a road. Is that a useful model of the geometry of a road? In some cases it is - and lots it is isn’t.

All of these are old issues and old debates being given new life in the age of the GeoWeb.

Separation Makes the Heart Grow Fonder

admin — Mon, 25 Jun 2007 18:00:00 +0000

An established principle in the IT and Web Worlds is the separation of presentation and content. In some ways a derivative of the famous Model-View-Controller paradigm introduced long ago by Xerox Parc, Separation of Content and Presentation, has fared well with the Web crowd - at least with the XML crowd … but DOES IT REALLY WORK? and DOES IT REALLY WORK FOR GEO STUFF? If I want to put a name on every street - how do I do it? I can apply a style to the names of the feature instances which uses some sort of “text along path” and presto - every street is named. Using a separate style I can ensure I have complete control over text placement, font and colour - and NONE of this is in the content!! All sounds great but what about handling label placement conflicts? How do I detect the intersection of a label with another label or with some other feature rendering? How do I do the cartographic finishing stuff that makes for a quality presentation? What if a street is made of many component street features - do I get many copies of the name - or do I have to have a complex model where the street is made of many segments (and thus I get only one) . How complex does it need to be?

3D Visualization in Geography - Moving to a 3D GeoWeb

admin — Fri, 22 Jun 2007 18:00:57 +0000

The world of 3D Geographic Visualization is certainly changing. Not long ago it meant little more than visualization of terrain surfaces or possibly the display of things like the distribution of temperature on the land or ocean surface. Times have changed. Now we have rich 3D content models in GML (cityGML), and visualizations in X3D and Collada. Our world is now populated by 3D buildings with photo-textured surfaces, and we have geo-immersive image environments with 3D freedom of movement. Furthermore, we are seeing big advances in the modeling of the built environment with the use of BIM (Building Information Model), IFC and cityGML. This further complemented by the integration of sensor data into the building environment to deal with issues from environmental management to perimeter security and surveillance - and here we see further GeoWeb technologies including OASIS Obix, the old GML, and the SWE (Sensor Web Enablement) - all part of a next generation of GeoWeb as an immersive 3D world. Of course the standards world has overlaps - not everyone uses KML for earth browser visualization. There are misunderstandings as to the meaning of feature and the importance of separating content and presentation. Some people think of Collada for content, while others insist it is only for visualization. Some browsers use Collada for building visualization and others use X3D. But convergence and rationalization is happening (note the Web3D Consortium) - and this will be a panel session at the GeoWeb 2007.

The 3D world presents many challenges - the need for exceptional performance â€“ the need for new navigation paradigms (e.g. drive along a street in the Earth Browser) - better integration of 2D and 3D views of the world (e.g. overlay restaurants in Google Earth and turn on 3D buildings) - the greater complexity of the entire environment and hence the need for much more sophisticated clutter management - better integration of real time sensor data - and the means to provide flexible user driven styling that accomodates both sensor data and geographic data in as smooth a manner as possible. Can it be done?

Microsoft On Board

admin — Tue, 19 Jun 2007 18:00:09 +0000

Microsoft will be returning as a Gold sponsor as well as co-sponsor of the popular fireworks reception along with Oracle Corporation. As part of the Gold sponsorship, Dr. Vincent Tao, director of Microsoft Local Search and the Virtual Earth division, will deliver a plenary speech on Thursday afternoon.

Microsoft will also deliver a workshop focusing on GeoRSS, Interoperability and the Microsoft Virtual Earthâ„¢ platform to take place on Monday, July 23 rd from 9:00am-12:00pm.