topic How to transform zonal and meridional velocity from regular lat lon to rotated lat lon in Map Projections Questions https://community.esri.com/t5/map-projections-questions/how-to-transform-zonal-and-meridional-velocity/m-p/823389#M185 <HTML><HEAD></HEAD><BODY><P>I am dealing with climate data(NCEP reanalysis data) which is in the regular lat lon coordinate system. I need to transform zonal and meridional velocity(u and v) from regular lat lon to rotated lat lon. I have seen this URL - <A href="http://jgrib.sourceforge.net/docs/rotLatLon.pdf" title="http://jgrib.sourceforge.net/docs/rotLatLon.pdf">http://jgrib.sourceforge.net/docs/rotLatLon.pdf</A>&nbsp; but I am not sure what this means -</P><P></P><P>"We also want to rotate horizontal vectors such as the wind. For this we need to calculate the meridional convergence at our position P. The convergence is defined as the local angle β from the regular meridian through the point P to the rotated meridian at P."</P><P></P><P><SPAN style="color: #222426; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgba(248, 248, 248, 0.6);">I need to know why meridional convergence is required here and the maths behind it. Does the wind vector pair need to be transformed together ?</SPAN></P><P></P><P><SPAN style="color: #222426; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgba(248, 248, 248, 0.6);">If this question is not suitable for this forum maybe coordinate reference system would be better ? </SPAN></P></BODY></HTML> Thu, 10 Dec 2015 03:27:55 GMT AswinDinakar 2015-12-10T03:27:55Z How to transform zonal and meridional velocity from regular lat lon to rotated lat lon https://community.esri.com/t5/map-projections-questions/how-to-transform-zonal-and-meridional-velocity/m-p/823389#M185 <HTML><HEAD></HEAD><BODY><P>I am dealing with climate data(NCEP reanalysis data) which is in the regular lat lon coordinate system. I need to transform zonal and meridional velocity(u and v) from regular lat lon to rotated lat lon. I have seen this URL - <A href="http://jgrib.sourceforge.net/docs/rotLatLon.pdf" title="http://jgrib.sourceforge.net/docs/rotLatLon.pdf">http://jgrib.sourceforge.net/docs/rotLatLon.pdf</A>&nbsp; but I am not sure what this means -</P><P></P><P>"We also want to rotate horizontal vectors such as the wind. For this we need to calculate the meridional convergence at our position P. The convergence is defined as the local angle β from the regular meridian through the point P to the rotated meridian at P."</P><P></P><P><SPAN style="color: #222426; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgba(248, 248, 248, 0.6);">I need to know why meridional convergence is required here and the maths behind it. Does the wind vector pair need to be transformed together ?</SPAN></P><P></P><P><SPAN style="color: #222426; font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 15px; background-color: rgba(248, 248, 248, 0.6);">If this question is not suitable for this forum maybe coordinate reference system would be better ? </SPAN></P></BODY></HTML> Thu, 10 Dec 2015 03:27:55 GMT https://community.esri.com/t5/map-projections-questions/how-to-transform-zonal-and-meridional-velocity/m-p/823389#M185 AswinDinakar 2015-12-10T03:27:55Z