heres an optomization if you use the other distance formula: distance = squareroot((x2-x1)^2 + (y2-y1)^2)
the square root takes a long time to compute, but the other math doesnt take too long. You might thing about squaring both sides and getting.. distance^2 = (x2-x1)^2 + (y2-y1)^2 that should be faster to calculate on the fly than trig and how you would use it would be if you wanted a list of all locations where the distance was less than 21, since both sides are squared you would check to see where the distance was less than 441 (21^2). When you get your results and want to display actual distances you could just square root them at that time ----- Original Message ----- From: "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Monday, November 01, 2004 7:33 AM Subject: Re: Witango-Talk: Distance Calculations - Sort on..., search on... > Jonah, > > to avoid a lot of calculations: I have allready short the formula. The > enclosed formula was only to show how it works finally. > Also I store allready the result for "SIN(<@COLUMN 'Adressen.Geo_Breite'>) / > COS(<@COLUMN 'Adressen.Geo_Breite'>)" in the database :-)) > > But this don't help me to make the sort or to make a search in a radius :-(( > > regards > > Daniel > > ----- Original Message ----- > From: "Jonah Simpson" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Sunday, October 31, 2004 9:10 PM > Subject: Re: Witango-Talk: Distance Calculations - Sort on..., search on... > > > > Hey Daniel! > > > > What database are you using? I know MySQL can do the trigonometric > > functions in a select statement and you could order your result from > > the database... > > > > Doing trig functions is pretty gross efficiency wise. You might want > > to store some of the functions that aren't going to change in your > > location table. ie. Have columns for: > > SIN(<@COLUMN 'Adressen.Geo_Breite'>) > > COS(<@COLUMN 'Adressen.Geo_Breite'>) > > in the same table that Adressen.Geo_Breite is stored in. As well, > > pre-calculate: > > COS(@@User$Breite_1) and > > SIN(@@User$Breite_1) to avoid doing this calculation 2500 times. > > > > You might want to play with that formula and optimize it. I'm not > > super hot with my trig identites, but I'm sure you could put it into a > > form that allows you to store as much information in the database as > > possible. Then you would only have to do a couple of calculations in > > your actual select statement. > > > > Interesting problem...let us know what route you eventually take. > > > > Cheers, > > Jonah Simpson > > [EMAIL PROTECTED] > > > > > > On Sun, 31 Oct 2004 19:22:39 +0100, [EMAIL PROTECTED] > > <[EMAIL PROTECTED]> wrote: > >> > >> Distance Calculation is no problem, that works. Here the formula: > >> > >> > >> <@CALC EXPR="ACOS(SIN(@@User$Breite_1)*SIN(<@COLUMN > >> 'Adressen.Geo_Breite'>) > >> + COS(@@User$Breite_1)*COS(<@COLUMN 'Adressen.Geo_Breite'>)*COS(<@COLUMN > >> 'Adressen.Geo_laenge'>-@@User$Laenge_1)) * 6378,388" Precision="1"> > >> > >> The problem what I have is: > >> > >> 1) To do a sort of the result (OK, I can do it in a array, but this need > >> to > >> much RAM [more as 2500 records, nearly 50x on one time]) > >> > >> 2) To do a search in a specified area like "show me all points near x > >> miles(km). > >> > >> One way what make sense is to store the formula in the database, but > >> - if i make a assign to a variable, then Witango store only the result. > >> What > >> I like to store is the formula-text: > >> > >> > >> Second problem: I can't do a sort on the stored formula (Sort command: > >> <@COLUMN 'Adressen.formel' Encoding="Metahtml">) > >> > >> Any Successions ? > >> > >> THX for help > >> > >> regards > >> > >> Daniel > >> > >> ________________________________________________________________________ > >> TO UNSUBSCRIBE: Go to http://www.witango.com/developer/maillist.taf > > ________________________________________________________________________ > > TO UNSUBSCRIBE: Go to http://www.witango.com/developer/maillist.taf > > > > ________________________________________________________________________ > TO UNSUBSCRIBE: Go to http://www.witango.com/developer/maillist.taf ________________________________________________________________________ TO UNSUBSCRIBE: Go to http://www.witango.com/developer/maillist.taf
