[GRASSLIST:4016] Re: Is Grass what I need?

[Benjamin Ducke]

I think what you need is a WebGIS, that is a system which makes
geographical data available over the internet.
Since it uses standard internet technology, such a system
can be accessed from any mobile device that has an internet browser
without the need to install any additional software on it.

If you want to work with two-dimensional, attributed vector data
you need to use a WebGIS that provides Web Feature Services (WFS).
In GIS terminology, a feature is a mathematical description of a 
geographical entity, e.g. a road network defined by the locations
of its intersections (nodes) and the length of segments in between (edges), 
also commonly refered to as vector maps.
The second important data structure in a GIS is raster data,
which stores one value for each cell in a regular grid of equal-sized
cells (like a satellite image).
Both vector and raster data has two and three-dimensional
variants (voxels in the case of raster data).

Again, I assume that your road networks are vector data of some
format (AutoCAD DXF/DWG, ArcGIS Shapefiles or whatever), so the
straight way is to look for a WebGIS that support WFS.
The alternative is to have the vector data rasterised on-the-fly by the
WebGIS and transmit as bitmap files over the internet.
This is called a Web Map Service (WMS).
Attributes will then still be queryable by the user but the amount
of data transfered over the internet line is much bigger, as
raster data need one unit of memory per cell, whereas vector data
only one per node (simply put).
Also, vector data scale more nicely on the screen, whileas raster
data will look blocky at some point (depending on the cell resolution) 
if you zoom in on it.

There are lots of open source WebGIS on the internet. Some are
ready-to-use solutions (like the famous UMN Mapserver http://mapserver.gis.umn.edu/)
, others come as a bunch of Java classes that you can put together for
a tailor-suited WebGIS.
I suggest you take a look at www.freegis.org where you will
find links to all the major projects.
GRASS also has a WebGIS engine called "GRASSlinks" but
I am not to sure about the status and maturity of it.

Since you also want to store the queryable attributes (e.g.
repair state of roads) in an SQL database system, you need
to make sure that the WebGIS can retrieve data from an
SQL database directly. As far as I remember, the PostgreSQL
database system is best supported by WebGIS (www.postgresql.org).
You should also take a look at PostGIS which allows you to
store both vector maps and attribute data in the same
database.

Other than that, search the web for literature on "WebGIS"
to get started. I think projects like yours have been
realised by the hundreds. There are also demo WebGIS servers
out there which you can log into and play around with some
demo data to see what they can do (again, try www.freegis.org
for links).

Hope this helps you on the way.

Cheers,

Benjamin


On Sat, 24 Jul 2004 10:45:47 +0200
"Lawrence Strydom" <jls at midafrica.com> wrote:

> Hi List,
> 
> I am completely new to the world of GIS and would appreciate any input  
>  from you old and wise GIS users.
> 
> Basically what I need to do is create a map depicting a network of roads  
> in a large geographical area. ( about the size of France) I will not be  
> using any relief maps so it is 2D data only. Now the map must be  
> accessible through a web browser, the user will have to be able to click  
> and zoom in to the required area of the map and add data or read data  
> which was added by other users. The data will not alter the propperties of  
> the map in any way but will simply be text which referrences a specific  
> point on the road. Eg: If a section of the road is in need of a specific  
> type of repair, then the inspector needs to be able to through his mobile  
> device access the map on the internet, click on that section of the road  
> and enter the text that states the road conditions at that point into a  
> form. THe coordinator back at HQ should then be able to read this and take  
> action accordingly.
> Just to make things a bit more interesting, all roads must be defined and  
> enterred in to a database against which reports can be run. Eg. a report  
> requesting the amount of potholes between town A and town B on route X.
> 
> As I said, I am not sure that I really need a GIS system to do this. If  
> anybody on this list has done anything simmilar or have any ideas, I would  
> love to hear from you!
> 
> Thanks in advance
> 
> -- 
> Lawrence Strydom
> Open Source Software Solutions Consultant
> email: jls at midafrica.com
> web: www.rpcdata.co.za
>            www.midafrica.com
> Tel: +27 (0)44 8770453
> Tel: +27 (0)21 4210882
> Mobile: 0833809341
> 
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