Open Source GIS Clients

I have had a number of companies recently approach me about open source GIS options. This has something to do with my recently published articles. One interesting area has been an investigation into Flex GIS clients. Openlayers is the premier Web 2.0 GIS client; well supported, a rich library filled with an array of functionality .. but written in Javascript. Now I have nothing against Javascript, its free, has a big community behind it and runs in the browser. But I'm a Flex developer. I prefer it because .. it has an excellent IDE which makes for easy debugging, developing sophisticated interactive application is both quick and easy, applications run the same in all browsers, actionscript is object oriented. Actionscript is just nicer and easier to work with .. in my view.

So enough. Anybody who argues against these opinions I would not oppose. Its just how I feel about it. Anyway, the whole Flex GIS open source client issue. I have worked with Modest Maps for sometime now to develop mostly consumer maps. Stop right there! Consumer maps? The world of online maps remains somewhat split. GIS maps and consumer maps. Consumer maps I define as the use of basemaps - tiles which are derived from satellite images or vector road maps for example - to build mash ups; video, imagery, text using, often, the addition of map markers for access (or clickable icons geospatially placed on the map). Here is a simple example. Google, Yahoo, Bing, mapquest offer largely API's for developing consumer maps.

So what are online GIS maps. A simple question? Well maybe. GIS has moved from the desktop to the Web. It was very much a niche market. Geography type nerds generating applications and analyses in large part for government (a generalisation but close to reality). The frustration for GIS vendors was how do they broaden the market. ESRI and the other key private vendors struggled to sell into the enterprise. They still do in fact.

Suddenly google maps arrived on the scene. It shook the mapping industry to its core. Internet maps were everywhere. Its worth noting that Mapquest preceded Google, but the fanfare (and $) waited for Googles arrival. Suddenly the other GIS vendors needed to react. ESRI produced rival online products. But with a GIS twist.

So here we are today. A plethora of consumer map APIs. And ESRI sitting in a somewhat awkward position offering free API's hooking easily into their own server product(s) ArcGIS (not so easily into other providers). Offering consumer and GIS API functionality. With a focus to sell their complete stack to those interested. Their purpose is to make money.

So how about those of us wanting to build online GIS maps, but avoid the high cost of the private vendor solutions? The open source GIS stack is very mature. But how about Flex clients?

I've spent some time looking at the options. Base requirements include:

- Rendering both WFS and WMS in combination
- Overlays of these services on various basemaps
- Drawing tools for line point and polygons
- Identify functionality

I looked at both Modest Maps and OpenScales. Though not its focus there has been some work done on Modest Maps toward some level of interaction with spatial servers. I added a WMS layer at:

http://www.flexmappers.com/mapserving/mapservingWMS/

Note, I had to make some tweeks to the WMS provider, provided with the library.

Openscales is less mature. But very impressive for how long development has been underway. I built the following map application:
http://www.flexmappers.com/mapserving/openscales.html

It supplies much of the base functionality I was looking to include. WMS is proving a little challenging (but i suspect a style tag is mssing from the tile request) and the map interaction is not a smooth as Modest maps. Only openstreetmap is provided, but I am looking to port code from Modest maps to add this functionality.

Ultimately Flex should simply be rendering the points, lines, and polygons supplied by the server.

I am interested to see how easy it might be to port from one library to the other. Either way, Openscales is a very interesting project. One well worth supporting.

Flex and PHP POST

I always forget the syntax when trying to get around the Flex sandbox and use PHP. On the Flex side we need the following:

[Bindable]private var pr_url:String;

..
private function init():void
{
..
pr_url = "url to SOAP service for example";
pr.send();
}

..

<mx:HTTPService id="pr" resultFormat="e4x" result="getMonths_result(event);" fault="getMonths_fault(event);" method="POST" url="http://www.flexmappers.com/puertorico/test.php">
<mx:request xmlns="">
<url>
{pr_url}
</url>
</mx:request>
</mx:HTTPService>

On the PHP side:

<?php

header('Content-Type: text/xml');
$url = $_POST["url"];

$data = file_get_contents($url);
echo $data;
?>

OpenScales

While becoming increasingly more impressed with Openlayers I came across OpenScales. A porting of sorts of Openlayers to Actionscript 3.0. Some key links below:

My OpenStreetmap, WMS, WFS Test
http://www.flexmappers.com/openscales

Code Examples
http://openscales.org/svn/openscales/trunk/openscales-fx-examples/src/main/flex/

Demo
http://openscales.org/openscales.swf

api
http://openscales.org/mvn-site/
http://openscales.org/mvn-site/openscales-core/asdoc/index.html

GetCapabilities Test
http://openscales.org/proxy.php?url=http://sigma.openplans.org/geoserver/ows?service=WFS%26request%3DGetCapabilities

PostGIS

Here is an excellent guide to working with PostGIS. Some of my additional notes:

Load Shapefile to PostGIS

a) DB Connect:
psql -d gisdb -h localhost -U matt

b) Generate sql file from shapefile:

C:\Program files\PostgreSQL\8.2\bin>shp2pgsql.exe data\states > states.sql

c) Use pgAdmin to ru sql (tools -> query tool. In query tool open->go to the states.sql

Paul Ramsey wrote PostGIS. I recently shared some emails with him. Thought part of the discussion worth reprinting:

Q. What is the difference between PostGIS and ArcSDE?

A. At a very high level (or perhaps this is a very low level), PostGIS /
PostgreSQL is a database, and ArcSDE is not. ArcSDE is a "spatial
middleware", it runs as a separate process and talks to the real
database below it. PostGIS is a "dynamically loadable runtime" inside
the PostgreSQL process -- it runs inside the same address space as
PostgreSQL, from the point of view of the computer, it's the all the
same program.

PostGIS should be viewed in exactly the same way relative to
PostgreSQL as Oracle Spatial should vis-a-vis Oracle, SQL Server
Spatial vis-a-vis SQL Server, Informix Spatial Extender vis-a-vis
Informix, etc, etc, etc. It works exactly the same way as all those
other in-process spatial type extensions to relational databases. So,
call it an "extension", a "spatial type", a "data blade", etc.
Unfortunately, years of marketing by various vendors have muddied the
terminological water surrounding type extension mechanisms.

The most important functional differences with SDE have nothing to do
with spatial database functionality and everything to do with ESRI
product placement and marketing. You'll find that ESRI products talk
more directly to ArcSDE than they do to PostGIS (or Oracle Spatial or
SQL Server Spatial, for that matter) because ESRI is interested in
selling their whole stack (desktop + server + web apps) to their
clients, not just the ArcGIS component. It's a non-trivial benefit for a customer that (a) already has a lot of ESRI software and (b) can afford the maintenance overhead in dollars, time and expertise that ArcSDE extracts.

GeoDjango

Wikipedia defines Django as follows:

"Django's primary goal is to ease the creation of complex, database-driven websites. Django emphasizes reusability and "pluggability" of components, rapid development, and the principle of DRY (Don't Repeat Yourself). Python is used throughout, even for settings, files, and data models."

The two key links for GeoDjango:

GeoDjango Online Docs

Django Docs

WMS and Bing/Yahoo Basemap Overlays

Here is an interesting issue I found today with WMS overlay. When WMS layers are created in either Mapserver or Geoserver then added as overlays to Yahoo or Bing their alignment is wrong.

Let me step back. As mentioned in earlier posts. One can create a WMS layer in geoserver and through the excellent config interface add this as a layer to Google earth.



All align perfectly. Now adding the same WMS to Modest Maps and overlaying it on Yahoo shows the WMS misaligned:



Turning to Openlayers, I find the same problem:



In each of the latter cases the WMS layer also looks stretched. I'll find the fix and post it.

Map Technology Overview

I've been on a technology review of late. Mostly driven by client requests. I never cease to be amazed by what is now available. So far my thoughts in brief:

Mapserver is a pain to configure. Manually writing mapfiles, takes me back to the days of ArcIMS and axl files. Geoserver is far easier in every respect. It has a terrific admin interface. Setting up basic map services, WMS, WFS is easy. Exporting in formats read by google maps etc is also a piece of cake. If it were not for the need of a full application server, the choice of geospatial server would be easy. Geoserver also allows for easy generation of Georss, KML and viewing of map layers in openlayers.

Caching and tiling is another area which favours Geoserver. Geowebcache is integrated into geoserver. No need for additional work. The config screen allows for easy seeding. Mapserver works with tilecache. From the work I have done so far you tile mapserver by calling tilecache and passing the mapserver url.

I'm still working with openlayers but am so far very impressed. One thing I already notice is how much is there. I really like the Modest Maps Flex library. But with a smaller community, it does not have the same depth of code. I'm still playing here, so more feedback later.

I'd like to know one of the big fours - mapquest, MSN, Yahoo and Google - API's. I lean towards mapquest, largely due to the feedback I have read and my impressions from conferences. I recently signed up for their developer account. A couple of people were soon emailing me with contact info. On one side I thought this great, since support might be more forthcoming. On the other side, money reared its ugly head. Use of this service beyond local testing has a price tag! Reminds me why I so favour open source.

Other areas on my radar at the moment beyond testing the mapquest API include:
- Geodjango testing
- PostGIS and shapefile write up
- Javascript to Flex/Flash communication

I'll write more on this in due course. I asked Paul Ramsey (OpenGeo and PostGIS author) his thoughts on Geoserver versus Mapserver. Here is his repy:

If you are deep into OGC standards, Geoserver has a big advantage in
completeness of implementations of things like SLD and WFS. (Less on
WMS).

I did a talk last year which, though tongue-in-cheek addresses the
more important differences. Which are philosophical more than anything
else. Scriptable web rendering engine vs complete spatial web
environment.

http://s3.cleverelephant.ca/geoweb-mapserver.pdf

Most of the speed differences are gone at this point, they perform
very comparably for common use cases.