[postgis-users] Client/Web based GIS using PostGIS

Thu May 25 07:57:05 PDT 2006

Shaun,
I have also developed WMS/SVG applications similar to what you are talking
about.  I think this is a very powerful way to go.  The really nice thing
about PostGIS is it can be set up to be very fast and minimal bandwidth with
some careful planning.
If you are interested, first go to http://www.carto.net
There are lots of examples and tutorials there.
There is also a web site I developed for a municipal client based on the
work done at carto.net that you can view at
http://www.udfcd.org/svg/svg_mapping.htm
All these examples work on IE+ASV, Firefox, Opera 9 (beta), Batik and Safari
(I think - don't have a Mac).  If the application were scaled back a bit it
might start working on a Mobile using Opera.

I am also in the process of developing some digitizing via script/SVG.  Not
ready yet but I can keep you posted.
Bruce Rindahl

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Randy
George
Sent: Wednesday, May 24, 2006 9:38 PM
To: 'PostGIS Users Discussion'
Subject: RE: [postgis-users] Client/Web based GIS using PostGIS

Hi Shaun,

	I have used svg as a client to public WMS/WFS services. It works
well where there is access to an svg renderer in the browser with decent
javascript capability. IE+ASV is still the best although FireFox with its
native svg rendering may soon be just as good. 
	It may be a bit iffy on PocketPC although there are some SVG Tiny
and SVG Basic implementations that might work at that level. I don't think
local draw and upload to the backing datastore could be done with SVG Tiny,
perhaps Basic? 

	I have doubts about 512/128 though for anything but a very simple
svg wrapping jpg image elements.

	A WMS server like GeoServer (open source) can provide static
background as an <image> element. SVG javascripting can provide the draw
capability you described. If you set up the GeoServer as a WFS-T the client
drawn elements can be pushed back to the PostGIS datastore. GeoServer also
has shp export (doesn't always work) capability and can serve data from
ArcSDE (not as well supported as PostGIS) Nice thing with OWS too is that
there are a number of public services that could be optionally stacked onto
the client as background. JPL, NOAA, USGS National Atlas ... You just want
to keep the pixel width and height optimized for the low bandwidth and
transparent image stacks won't work unless you use png which are always
larger than jpg.

	As far as caching it just depends how much you want to do on the
client. If the <image> element is entirely static i.e. no zoom and pan from
the WMS server you can just href the preset image from a local file
location. As an SVG image element you still have some zoom and pan within
the limits of the image. It might be interesting to look at a small tile set
for a local pan capability.
	If it is more complex you could of course setup a local service on
the client, but that would be a lot of work for anything more than 1 or 2
clients. You would need to install:
Apache Tomcat + PostgreSQL/PostGIS + GeoServer + datastores as well as the
client browser stuff for svg.

Obviously not possible on a handheld of any kind.

Randy

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Shaun
Kolomeitz
Sent: Wednesday, May 24, 2006 5:39 PM
To: postgis-users at postgis.refractions.net
Cc: Shaun Kolomeitz
Subject: [postgis-users] Client/Web based GIS using PostGIS

I wonder if I could pose some questions please for some collective
advice/directions?

I'd like to set-up a situation where remote sites (over 50 on a poor 512/128
satellite connection, many more on ADSL or WAN) can add and view
spatial/non-spatial data using some form of web-client or a relatively
"low-fat" / customisable  (desktop) client. The user will need to see some
background (raster and vector) data and be able to digitise on-screen as
well as import shapefiles (usually converted from Garmin GPS data). In terms
of getting over the crappy upload/download is there a way I could use a
"cache" concept where locally used data can be downloaded to the client and
new data uploaded (overnight or on the weekend ?) when the connection is not
being used for other purposes ??? I'd like to bring in handheld (PocketPC)
clients as well, but I suspect this may be more difficult.

The requirements are pretty straightforward (?) - allow users to add spatial
data (points, lines and polygons), pop-up some standard forms based on the
type of feature they are adding (a fire boundary, a pest or weed location or
distribution, a monitoring site etc), allow users to upload photo point (and
other) images to the server, provide hot-links to non-spatial data (Word
docs, HTML pages etc). Typically we try to walk before we can run and like
to start with something simple and easy to use and build on it from there
(taking the users with us, rather than dumping them into the deep end of a
complicated and intricate process). Can I use PostGres/PostGIS to store,
retrieve and display georectified and non-spatial images ?

I've set-up PostGRES/PostGIS and have tested uDIG (which looks fantastic
BTW) as well as Quantam GIS (which allows me to update PostGIS), but I'm
also keen on "thin" (web-ish?) approaches like perhaps having an SVG window
(what is better/best ?) for update purposes. I assume I can get away with a
WMS (image) for "displaying" data, but would need a more "intelligent"
window to permit updating. I'd also like to be able to distribute some data
out via a WFS/WMS to other related (but not necessarily internal clients)
who may be using MapInfo or ArcGIS products. There is an in-house ESRI
standard so I really need to funnel data to/from ArcSDE / shapefile for
broader Dept consumption on ArcGIS products.

Sorry to raise so many questions. However I get the feeling from what I am
seeing that the Open and Free-er GIS products have really matured to a point
where they are real contenders (and in some ways better) than their
proprietary commercial cousins.

The first question is - Is it possible ? The second question is - How might
I go about it ? I'll deal with the co$ts/resources later.
I'm happy to go off-line to discuss this and send a summary back to the list
if appropriate.

Thanks in advance,
Shaun Kolomeitz
Senior Technical Officer
Systems & Support Branch
Parks Division
Environmental Protection Agency

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