From: Hiroyasu Yasuda <hyasuda@ce...>  20071210 23:11:42

On 2007/12/10, at 23:41, Andrew Ross wrote: > On Mon, Dec 10, 2007 at 11:11:42PM +0900, Hiroyasu Yasuda wrote: >> >> On 2007/12/10, at 17:53, Arjen Markus wrote: >> >>>> Dear all: >>>> >>>> I would like to plot vectors in general curve coordinate as >>>> attached >>>> picture. Of course I have already try to be plotting with plvec2. >>>> When I gave the vector data which is u =1.0 and v=0.0, the plotted >>>> vectors look like along coorthogonal coordinate. >>>> >>>> I think that plplot has the vector plotting function in general >>>> curve >>>> coordinate because I read the reference of plplot and sample >>>> code of >>>> x22f. Can we plot that things? >>>> >> >> Hello Arjen: >> >>> that means that the components of the vector are not cartesian >>> but based on the (local) coordinate system (or grid orientation)? >> >> Yes, that is, I have been computing with local coordinate system. >> >>> That means that PLplot will have to keep track of this more general >>> coordinate system. Isn't it simpler to convert the components from >>> the curve coordinate system to the cartesian plotting coordinates? >> >> When I'm computing and then plot the vectors with local coordinate >> system, do we have to convert the vector component to plot the >> vectors along local coordinate under plplot? > Hello, Andrew: > The vector components are always assumed to be cartesian. As Arjen > said, if you want to use local coordinates for the vector components, > you need to convert them to cartesian cordinates before plotting. I understand that you mention. However, the plplot reference of plvec2 in Chapter 20 said that: NOTE: this function is intended for use from a Fortran 77 caller only. The C user should instead call plvect using the builtin transformation function pltr2 for the same capability. Can we plot directly the vectors along curve coordinate with plvec2 ? Regards, Hiro 