[postgis-users] Create circles using a formula

[pcreso at pcreso.com]

I'm not conversant with geoserver but have used mapserver to do this sort of thing often enough.

I assume your data is in PostGIS, which means your mapserver DATA statement can be an embedded SQL query or a PostGIS view.

You can create a view on your table, along the lines of:

create view v_table 
as select *, buffer(setsrid(makepoint(lon, lat),4326),<formula to calculate radius>) as geom
from table;

(assuming you want the output data in EPSG:4326)

or you can set up your process to build the geometry in a physical table doing much the same thing, perhaps as an update or insert trigger?

Use this view, or table as the "table" you provide the WFS service from, & the geometries you are providing will be suitably sized circles.

Note this assumes a constant signal strength unchanged by topography, which is very simplistic.

Tools like GRASS allow you to apply a terrain model to the sites & carry out a line-of-sight analysis to generate more accurate polygons descibing the expected coverage from a tower.

If you are displaying thousands of features, you might find WMS with srever side rendering gives a better response time than WFS. Geoserver can provide both WMS & WFS services, but I think mapserver has some advantages in the WMS arena.

HTH,

  Brent Wood
                                 
 
On 02/06/2011, at 3:55 AM, vikashvikky wrote:

> 
> Hi,
> 
> I am doing a project for a telecom company. I have to render circles on the
> map(assuming the center of the circle as tower and circle as the area
> covered by that signal), I am using base layers as Google Maps,Yahoo
> maps(Spherical Mercator) So I have used CreateGeodesicPolygon() successfully
> to create circles by reading the values from DB.
> 
> Now Since I have to render lot of circles, it made me switch to geoserver.
> Since the data is being provided by telecom company , they provide
> Lat,Lon,Gt,Gr,Pt,Pr,lambda(I think their meaning is irrelevant here) values.
> These values are stored in the database as they are. Now should use a
> equation(FRIIS transmission equation) and substitute each row(of a tower)
> values to find the distance covered by the tower.Then I have to create
> circles with that distance(considered as radius) and lon/lat and render them
> on map using geoserver.
> 
> Please suggest me any ideas of how to carry on this task.... I wud be
> thankful to your guidance
> -- 
> View this message in context: http://old.nabble.com/Create-circles-using-a-formula-tp31752667p31752667.html
> Sent from the PostGIS - User mailing list archive at Nabble.com.
> 
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