matplotlib-users Mailing List for matplotlib

On Wed, 2004-12-22 at 17:30 -0600, John Hunter wrote:

>  - 4x image speedups for large images

This is a biggie!!  Ladies and gentlemen, my impression is that imshow
is now at least as fast as, and perhaps faster than, DS9 for
astronomical image display.  (I'm looking at 1024 square full disk solar
images.)  Nice job, John.

Happy happy to all,
Steve

John,

Many thanks for the lengthy and thorough explanations on transformations 
in matplotlib. I am working my way through them and the source files. I 
am still trying to get my line+triangle example to work; i think it 
might be flexible in the end, if we want to, e.g., position the head 
anywhere along the stem, or use different polygons for the head. Your 
polygon example is certainly flexible for shaping the arrow, but for 
instance, if i want to draw an 'oriented path' in 2d space, it will 
become more complicated.

I can now position the stem correctly and the head 'almost' correctly 
using offsets. Here is what i have in my Arrow class:

  orig, dest = zip( xdata, ydata )
  self._x = tuple( xdata )
  self._y = tuple( ydata )
  self._center = dest    # Temporary
  radius = 4

  # Stem
  self._stem = Line2D( self._x, self._y, **kwargs )
  self._stem.set_transform( ax.transData )

  # Head
  self._head = RegularPolygon( tuple(self._center), 3, 

      radius = radius, orientation = angle, **kwargs )
  trans = identity_affine()
  trans.set_offset( tuple( dest ), ax.transData )
  self._head.set_transform( trans )

and the draw() method just says:

  def draw( self, renderer ):
         # Draw stem and head
         self._stem.draw( renderer )
         self._head.draw( renderer )

You instantiate it, for example, with:

  ax = axes( [0.1, 0.1, 0.8, 0.8], polar = polar )
  ax.set_xlim( [0,10] )
  ax.set_ylim( [0,10] )
  arr = ax.arrow( [1, 4], [1, 5] )

to draw an arrow from (1,1) to (4,5).

There are two things:
1) I know the center of the arrow head isn't right; i'll shift it later
2) The arrow is drawn correctly (even on polar axes) but there is a 
slight gap between the tip of the stem and the bottom of the head; 
although the center should coincide with the tip (called 'dest' in the 
code excerpt).

Why isn't the triangle centered where the tip of the stem is?

Dominique

>
>
>    John> Thanks very much indeed -- that has me sorted.  I'll give
>    John> imshow a go as well when I get a chance.
>
>    John> I've attached an image of the results to give you an idea
>    John> what I'm up to.
>
>Very nice..  what do the colors represent, pray tell? 
>
Nothing too exciting I'm afraid. I've got this object I call an atlas 
which is a collection of maps. Each map specifies the list of shapes 
(=countries/states/counties etc) that make up the particular map.

Anyway, to produce this picture I just numbered each country according 
to the order it appears in the list in my 'World' map. This is just a 
toy I've been using for testing.

> Also, in case
>you missed the announcement for 0.65, matplotlib now a number of new
>colormaps, in addition to the trusty jet.
>
>   autumn bone cool copper flag gray hot hsv jet pink prism spring
>   summer winter
>
I did see that -- I'll have to see about making the colour map choice 
available to everyone (or maybe just check today's date and use spring, 
summer, autumn, winter as appropriate).

John

>>>>> "John" == John Gill <jn...@eu...> writes:

    John> Thanks very much indeed -- that has me sorted.  I'll give
    John> imshow a go as well when I get a chance.

    John> I've attached an image of the results to give you an idea
    John> what I'm up to.

Very nice..  what do the colors represent, pray tell?  Also, in case
you missed the announcement for 0.65, matplotlib now a number of new
colormaps, in addition to the trusty jet.

   autumn bone cool copper flag gray hot hsv jet pink prism spring
   summer winter

    John> I can't praise matplotlib highly enough, it has done 90% of
    John> the hard work in getting a very handy mapping tool together
    John> in a matter of days.

Great - thanks for the encouragement.

    John> Hope Santa brings you what you deserve.

With three kids, why do I get the feeling I won't be on the receiving
end of Christmas this year? :-)

JDH

>>>>> "John" == John Gill <jn...@eu...> writes:

    John> I'm having trouble getting the alpha keyword to do anything
    John> when I use the OO interface (as per gtk embeded example).

I'm not sure about the exact status of alpha vis-a-vis alpha - perhaps
Steve can clarify.  a gdk.Color does not have and alpha channel, nor
does a gdk.GC, but a gdk.Pixbuf does.  Basically, alpha is (mostly)
unsupported on the GTK backend (you can do alpha blending of images
because antigrain handles images across backends).  

But you should probably be using the gtkagg backend, which has alpha
support for all plot elements, and does a better job of anti-aliasing.
In some measurements, eg animation, it is a little slower than the
pure GTK backend, so you may want to do a little profiling.  It will
probably be faster than GTK for large collections, perhaps 2x or so,
since it does the collection drawing in extension code and the other
backends have a python implementation.

    John> Aside from this, I'd just like to say what a great package
    John> matplotlib is.  I've been using it a lot the last week to
    John> plot maps -- first I started using pcolor to plot hurricane
    John> footprints (I'll see if I can get the OK to release some of
    John> the plots, pcolor produced some wonderful pictures with a
    John> few lines of code).

if/when you have regularly spaced grids, imshow will likely be an
order of magnitude faster than pcolor for large data sets, so keep it
in mind....

    John> Inspired by this I've also been plotting simple maps by
    John> creating collections of polygons (eg one polygon for each
    John> country in the world) + associating a value with each
    John> polygon.  Again, great pictures in a few lines of code +
    John> using the collections the speed is pretty good, even with
    John> 3000+ polygons it was all pretty snappy.

    John> I'll see if I can get an example together -- to do this I'll
    John> need to get some un-restricted shape files, but I'll see
    John> what I can do.

That would be great - I'll keep my eyes peeled...

JDH

I'm having trouble getting the alpha keyword to do anything when I use 
the OO interface (as per gtk embeded example).

The attached code demonstrates the problem.

With matlab_test() I get alpha blending as expected, with the 
gtk_embed_test() it seems to be ignored.

Aside from this, I'd just like to say what a great package matplotlib 
is.   I've been using it a lot the last week to plot maps -- first I 
started using pcolor to plot hurricane footprints (I'll see if I can get 
the OK to release some of the plots, pcolor produced some wonderful 
pictures with a few lines of code).

Inspired by this I've also been plotting simple maps by creating 
collections of polygons (eg one polygon for each country in the world) + 
associating a value with each polygon.  Again, great pictures in a few 
lines of code + using the collections the speed is pretty good, even 
with 3000+ polygons it was all pretty snappy.

I'll see if I can get an example together -- to do this I'll need to get 
some un-restricted shape files, but I'll see what I can do.

Many thanks for matplotlib.

John