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. > 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
