Hi all, I'm an absolutely matplotlib newbie, so I'm sorry if my question is trivial. Anyway I've read the user guide and looked at the examples without finding out a solution. Here it is my problem. Suppose I have a 2-dimensional array containg my data, and I want to produce a surface or a contour plot with it. Now the imshow() function seems the right way to go through. So far so good. Now suppose I want to draw the x,y axes for this plot, and suppose my axes are represented by **not-uniform** 1-dimensional array x[i], y[j]. How can I get the right ticks on the plot axes?? I hope to have been clear. Thanks in advance, Andrea.
>>>>> "Andrea" == Andrea Riciputi <ari...@pi...> writes: Andrea> Hi all, I'm an absolutely matplotlib newbie, so I'm sorry Andrea> if my question is trivial. Anyway I've read the user guide Andrea> and looked at the examples without finding out a solution. Andrea> Here it is my problem. Suppose I have a 2-dimensional Andrea> array containg my data, and I want to produce a surface or Andrea> a contour plot with it. Now the imshow() function seems Andrea> the right way to go through. So far so good. Now suppose I Andrea> want to draw the x,y axes for this plot, and suppose my Andrea> axes are represented by **not-uniform** 1-dimensional Andrea> array x[i], y[j]. How can I get the right ticks on the Andrea> plot axes?? You need to interpolate your data onto a rectilinear grid and then use pcolor. imshow requires that your data be an image -- eg the dx and dy between rows and columns is the same between every row and column. pcolor only assumes a rectilinear grid, so the dx and dy can vary from row to row and column to column. But you have unstructured data. In matlab, the interpolation is handled by the griddata function. Peter Groszkowski promised to post some code he uses to for this purpose back in December, but apparently he got lost in the stars. matlab uses a delaunay triangulation according to the documentation for griddata -- I think Peter uses a different approach. I looked at the scipy interpolate module but didn't see anything that looked just right -- perhaps I missed it. It surprises that scipy doesn't have a delaunay triangulation routine, but apparently it does not. A quick google for revealed http://www.python.org/pypi?:action=display&name=Delny&version=0.1.0a2 which relies on the gnu qhull library... A griddata function for mpl would be a nice complement to the meshgrid function. JDH
On Feb 25, 2005, at 12:40 PM, John Hunter wrote: >>>>>> "Andrea" == Andrea Riciputi <ari...@pi...> writes: > > Andrea> Hi all, I'm an absolutely matplotlib newbie, so I'm sorry > Andrea> if my question is trivial. Anyway I've read the user guide > Andrea> and looked at the examples without finding out a solution. > > Andrea> Here it is my problem. Suppose I have a 2-dimensional > Andrea> array containg my data, and I want to produce a surface or > Andrea> a contour plot with it. Now the imshow() function seems > Andrea> the right way to go through. So far so good. Now suppose I > Andrea> want to draw the x,y axes for this plot, and suppose my > Andrea> axes are represented by **not-uniform** 1-dimensional > Andrea> array x[i], y[j]. How can I get the right ticks on the > Andrea> plot axes?? > > You need to interpolate your data onto a rectilinear grid and then use > pcolor. imshow requires that your data be an image -- eg the dx and > dy between rows and columns is the same between every row and column. > pcolor only assumes a rectilinear grid, so the dx and dy can vary from > row to row and column to column. But you have unstructured data. > I'm not sure if that is what is being said. What may be referred to is a structured 2-d image for which it is intended that the data coordinates be taken from the x and y arrays (for corresponding locations). The contour task does allow one to give such x and y arrays, but not the image display tasks (if I remember correctly). Some clarification is needed. Perry
John Hunter wrote: >>>>>>"Andrea" == Andrea Riciputi <ari...@pi...> writes: >>>>>> >>>>>> > > Andrea> Hi all, I'm an absolutely matplotlib newbie, so I'm sorry > Andrea> if my question is trivial. Anyway I've read the user guide > Andrea> and looked at the examples without finding out a solution. > > Andrea> Here it is my problem. Suppose I have a 2-dimensional > Andrea> array containg my data, and I want to produce a surface or > Andrea> a contour plot with it. Now the imshow() function seems > Andrea> the right way to go through. So far so good. Now suppose I > Andrea> want to draw the x,y axes for this plot, and suppose my > Andrea> axes are represented by **not-uniform** 1-dimensional > Andrea> array x[i], y[j]. How can I get the right ticks on the > Andrea> plot axes?? > >You need to interpolate your data onto a rectilinear grid and then use >pcolor. imshow requires that your data be an image -- eg the dx and >dy between rows and columns is the same between every row and column. >pcolor only assumes a rectilinear grid, so the dx and dy can vary from >row to row and column to column. But you have unstructured data. > >In matlab, the interpolation is handled by the griddata function. >Peter Groszkowski promised to post some code he uses to for this >purpose back in December, but apparently he got lost in the stars. > yup.. i did get a little "lost in the stars" - I forgot about it in fact. I promise I will post it in the next few days - this time I mean it. ;) -- Peter Groszkowski Gemini Observatory Tel: +1 808 9742509 670 N. A'ohoku Place Fax: +1 808 9359235 Hilo, Hawai'i 96720, USA