Hi Blake, I have done this sort of thing pretty often... I find PostGIS makes it pretty easy.
My approach is to generate an arbitrary equal area projection which reasonably robustly covers the area of interest. (Let me know if you need a hand with this) The buffering query then transforms the lat/long point into this coordinate system to generate the buffer, then transforms the result back to lat/long. This does generate "circles" which are not round in a lat long "projection". eg: (assume your new equal area projection is SRID:100000 in a geometry column called circle & your lat/long data is SRID:4326 called point & the buffer distance is $NM) update <table> set circle=transform(buffer(transform(point,10000),1852*$NM),4326); This uses your new projection to generate the correct buffer, but all input is lat/long as is the output.... Of course you can add another parameter to buffer to set the number of points you want to define the circle. HTH, Brent Wood --- On Fri, 9/12/08, Blake Crosby <[EMAIL PROTECTED]> wrote: > From: Blake Crosby <[EMAIL PROTECTED]> > Subject: [postgis-users] Buffer/Nautical Miles > To: "PostGIS Users Discussion" <[email protected]> > Date: Friday, September 12, 2008, 8:36 AM > I'm trying to create "circles" by using the > buffer function around a point. > > The radius values i'm working with are in nautical > miles. The definition > of a nautical mile is 1 minute of 1 degree. > > Since this unit of measurement is based on a degree, and > WSG84 is based > on degrees of lat/long (and not meters like UTM) will the > following be > valid for a circle with a radius of 2 nautical miles around > point > (72.3,-45.3)? > > st_buffer(st_geomfromtext('POINT(-45.3 72.3)', > 4326), 0.0166667*2) > > I'm trying to troubleshoot a problem I'm having and > want to rule out any > issues with my usage of buffer. > > Blake > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
