On Sun, Aug 23, 2009 at 11:34 AM, P Kishor<punk.k...@gmail.com> wrote: > On Sun, Aug 23, 2009 at 11:11 AM, Simon > Slavin<slav...@hearsay.demon.co.uk> wrote: >> >> On 23 Aug 2009, at 5:00pm, P Kishor wrote: >> >>> WHERE a*x - y + c = 0 >> >> Here's the problem. This works only when the equation is exact. > > Indeed. We already laid out those presumptions. One, your height > coverage has to be continuous as you can get via an image. Two, you > can substitute any equation for your line, however, any complex line > can be broken up into segments of simple, straight lines. All GIS > software do just that. Once you can solve the problem for a simple > segment, you can repeat the solution for every segment in the line. > > Postgis/Spatialite by themselves won't solve the problem, but they may > have (don't know about Spatialite, but Postgis has a boatload of > geographic functions created by the developers) ready made functions > that can help build the solution. > > A really nice application would allow the user to click, click, click > a line (of many segments) on a representation of a terrain, go > retrieve the height values, and construct an image of the elevation > profile. >
Kinda like http://veloroutes.org/bikemaps/ > >> Which >> under normal circumstances means that all the numbers fit neatly with some >> imaginary integer formula. This isn't how real life works, especially when >> you've correctly noted that your measured heights weren't measured at >> exactly regular intervals. >> >> You're going to have to do some proper programming. For example, how to >> interpolate the height at an arbitrary position when you have a collection >> of heights measured nearby. There's no easy solution and you certainly >> can't do the majority of the work inside a SQL query. >> >> Simon. >> > > > > -- > -- Puneet Kishor http://www.punkish.org Carbon Model http://carbonmodel.org Charter Member, Open Source Geospatial Foundation http://www.osgeo.org Science Commons Fellow, http://sciencecommons.org/about/whoweare/kishor Nelson Institute, UW-Madison http://www.nelson.wisc.edu ----------------------------------------------------------------------- Assertions are politics; backing up assertions with evidence is science ======================================================================= Sent from Madison, WI, United States _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
