----- Original Message ----- From: "Peter" <[email protected]> To: <[email protected]> Sent: Wednesday, April 09, 2014 1:40 PM Subject: Re: [rrd-users] How store wind vector data?
> The 359-0 problem can solved easy by changing from polar coordinate system > (velocity+direction) to cartesian coordinate system: > Wind_X = velocity * cos(direction * PI / 180) > Wind_Y = velocity * sin(direction * PI / 180) > > The normal AVERAGE aggregate function can applied to Wind_X and Wind_Y. > > The back transformation is: > velocity = Sqrt(Wind_X*Wind_X + Wind_Y*Wind_Y) > direction = Atan2(Wind_Y, Wind_Y) * 180 / PI > > I read in the rrd documentation, that calculated data source are possible. > So a solution would be: > Define 2 data source Wind_X, Wind_Y. > The update program has calculate Wind_X, Wind_Y from velocity+direction. Yeah, this could work. Split the wind into components, do this outside RRDtool. For graphing and printing purposes you can combine the components using CDEF. > Can I define velocity and direction as calculated data source with the > formulas? > velocity = Sqrt(Wind_X*Wind_X + Wind_Y*Wind_Y) > direction = Atan2(Wind_Y, Wind_Y) * 180 / PI Never mind the exact formulas (i've seen your other post). Yes, this should be possible with CDEF, although you may have to rewrite some of the math. _______________________________________________ rrd-users mailing list [email protected] https://lists.oetiker.ch/cgi-bin/listinfo/rrd-users
