matplotlib-users Mailing List for matplotlib

On 11/10/2007, Jeff Whitaker <js...@fa...> wrote:

> but I think you want
>
> values, lon = basemap.shiftgrid(180, values, lon, start=False)

Thats it! Thanks a lot!

Cheers

Adam

Disclaimer: I do know Python, but am not terribly familiar with Matplotlib as 
I'm taking over the maintenance of our graphing libraries.  This post is 
likely to leave out details that you need to help diagnose the problem, but I 
didn't think posting all 1500 or so lines of our graphing routines would be 
that helpful at this point. :)

As you can see from the attached graph, there is a break the in graph 
somewhere around 7 AM or so.  This is the data I am graphing for that red 
line:

"2007-10-09 00:00:00",0.015
"2007-10-09 01:00:00",0.015
"2007-10-09 02:00:00",0.014
"2007-10-09 03:00:00",0.012
"2007-10-09 04:00:00",0.008
"2007-10-09 05:00:00",0.002
"2007-10-09 06:00:00",-0.006
"2007-10-09 07:00:00",1.068
"2007-10-09 08:00:00",12.8
"2007-10-09 09:00:00",15.21
"2007-10-09 10:00:00",20.13
"2007-10-09 11:00:00",20.94
"2007-10-09 12:00:00",21.15
"2007-10-09 13:00:00",21.13
"2007-10-09 14:00:00",20.88
"2007-10-09 15:00:00",20.72
"2007-10-09 16:00:00",20.55
"2007-10-09 17:00:00",16.28
"2007-10-09 18:00:00",13.18
"2007-10-09 19:00:00",4.342
"2007-10-09 20:00:00",0.016
"2007-10-09 21:00:00",0.015
"2007-10-09 22:00:00",0.015
"2007-10-09 23:00:00",0.015

If I change the -0.006 at 6:00AM to 0.006, it graphs with no break in the 
line.  This is not a big deal to me, but it is a big deal to the consumer of 
these graphs.  Could this be a bug in matplotlib, or is it more likely a bug 
in what we're doing with the data (almost nothing) before it gets to the 
matplotlib graphing routines?

Thanks for any insight you can give.

j

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Adam Mercer wrote:
> On 11/10/2007, Jeff Whitaker <js...@fa...> wrote:
>
>   
>> Adam:  I assume your data is on a latitude-longitude grid?  You've asked
>> for a mollweide projection centered on the Greenwich meridian.  Your
>> data is not centered on Greenwich - but the error message is trying to
>> say that you can shift your grid (with the shiftgrid function) so that
>> is has the same orientation as the map projection region.  This only
>> comes into play with global projections that 'wrap-around' at the edges,
>> like the mollweide and mercator projections.  The orthographic
>> projection does not 'wrap around' - hence you don't get the error message.
>>     
>
> Looking at the shiftmap function it looks like I should shift the
> co-ordinate grid so that my longitude runs from -180 to 180 instead of
> 0 to 360, therefore the following shiftgrid call should do this
>
> values, lon = basemap.shiftgrid(180, values, lon)
>
> However I still get the same error and the corruption in the resulting
> plot.  I feel like I'm missing something obvious here but can't find
> it.
>
> Cheers
>
> Adam
>   
Adam:

 From the basemap docs;

shiftgrid(lon0, datain, lonsin, start=True)
    shift global lat/lon grid east or west.
    assumes wraparound (or cyclic point) is included.
     
    lon0:  starting longitude for shifted grid
           (ending longitude if start=False). lon0 must be on
           input grid (within the range of lonsin).
    datain:  original data.
    lonsin:  original longitudes.
    start[True]: if True, lon0 represents the starting longitude
    of the new grid. if False, lon0 is the ending longitude.
     
    returns dataout,lonsout (data and longitudes on shifted grid).


You did

values, lon = basemap.shiftgrid(180, values, lon)

but I think you want

values, lon = basemap.shiftgrid(180, values, lon, start=False)

HTH,

-Jeff

-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
Meteorologist               FAX    : (303)497-6449
NOAA/OAR/PSD  R/PSD1        Email  : Jef...@no...
325 Broadway                Office : Skaggs Research Cntr 1D-124
Boulder, CO, USA 80303-3328 Web    : http://tinyurl.com/5telg

On 10/11/07, Alexander Schmolck <a.s...@gm...> wrote:
> Hi,
>
> I'm using matplotlib in a C++ app (with a qt4 gui), by embedding python with
> boost::python. The C++ app calls Py_Initialize(), init_myplottingmodule(), and
> boost::python::import("matplotlib.pylab") once on startup and certain GUI
> events then fire up a matplotlib window via calls like this one:
>
> // simplified version
> void plotCurve(){
>     clf();
>     title("Diagonal line plot");
>     double O1[] = {0,1};
>     plot(std::vector<double>(O1,O1+2), std::vector<double>(O1,O1+2), "b:");
>     show();

Eeeeew, that looks really dangerous.  For starters, I would never try
to do this using pylab, but rather follow the lead of
examples/embedding_in_qt.py.  Then you won't be competing for the
mainloop....

JDH

On 10/11/07, Charles Seaton <cs...@st...> wrote:

> Any suggestions on how to get either matplotlib.dates.datestr2num or
> dateutil.parser.parse to properly handle timezone information in the
> datestring would be greatly appreciated.

Not sure how to answer this question vis-a-vid dateutil.parser, but
you may want to consider creating your own datestr -> datetime
converter using time.strptime and then allowing mpl to convert to
numbers using date2num.  I think you can use the %Z format code for
timezones.

JDH

I am having some problems getting matplotlib.dates.datestr2num to handle
timezones in the datestring.

>import matplotlib
>matplotlib.dates.datestr2num('Jan 1, 2007 12:00 PDT')
732677.83333333337
>matplotlib.dates.datestr2num('Jan 1, 2007 12:00 PST')
732677.83333333337
>matplotlib.dates.datestr2num('Jan 1, 2007 12:00-08')
732677.83333333337
>matplotlib.dates.datestr2num('Jan 1, 2007 12:00 UTC')
732677.5
>matplotlib.dates.datestr2num('Jan 1, 2007 12:00 EST')
732677.5
>matplotlib.dates.datestr2num('Jan 1, 2007 12:00-07')
732677.79166666663

The problem appears to lie with dateutil, as direct use of the
dateutil.parser.parse function shows the same problem:

> import dateutil.parser
> dateutil.parser.parse('Jan 1, 2007 12:00 EST')
datetime.datetime(2007, 1, 1, 12, 0)
> dateutil.parser.parse('Jan 1, 2007 12:00 PDT')
datetime.datetime(2007, 1, 1, 12, 0, tzinfo=tzlocal())
> dateutil.parser.parse('Jan 1, 2007 12:00 PST')
datetime.datetime(2007, 1, 1, 12, 0, tzinfo=tzlocal())

I am using dateutil version 1.2.

Any suggestions on how to get either matplotlib.dates.datestr2num or
dateutil.parser.parse to properly handle timezone information in the
datestring would be greatly appreciated.

Charles Seaton
OHSU/CMOP
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View this message in context: http://www.nabble.com/datestr2num%2C-dateutil.parse-and-timezone-problems-tf4609462.html#a13162968
Sent from the matplotlib - users mailing list archive at Nabble.com.

Hi Yadin,

I am a simple user, but I already faced this problem. The idea I used is 
to plot the data as an image, with magnitudes being converted in color 
levels.

To do that, you have to define an array (let's say 'Z', Z(x,y) with dims 
len(X) and len(Y) and fill it with tour magnitudes. Then you have a two 
dimensional array that you display as an image using :

im = pylab.Imshow(Z)

Imshow has a lot of options you can use to customize your display, and 
you can add a colorbar with :
pylab.colorbar()

I have some examples of such scripts, but commented in French, so 
perhaps not very useful for you.

See the user's guide to begin, p 38 for example.

Regards,
Alain

yadin Bocuma Rivas a écrit :
>
> I i have tree lists or array of values
> list x of 100... values
> list y of 100.. values
> list mag of 100.. values
> list x and y are coordiantes of points
> and list Mag is magnitude of something at that point
>
> how can i plot this quantities using matplotlib, any function please?
>
> my code starts as.....i need to plot the points vhat can i use?
>
> from __future__ import division
> from matplotlib.patches import Patch
> from pylab import *
>
> def func3(x,y):
>     return (1- x/2 + x**5 + y**3)*exp(-x**2-y**2)
>
>
> # make these smaller to increase the resolution
> dx, dy = 0.5, 0.5
>
> X = arange(-3.0, 3.0001, dx)
>
> Y = arange(-3.0, 3.0001, dy)
>
> Mag= X**2+Y**2
>
> ?????(X, Y, Mag)
> colorbar()
> axis([-3,3,-3,3])
> savefig('three d plot of points making a surface')
> show()
>
>
> ------------------------------------------------------------------------
>
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On 11/10/2007, Jeff Whitaker <js...@fa...> wrote:

> Adam:  I assume your data is on a latitude-longitude grid?  You've asked
> for a mollweide projection centered on the Greenwich meridian.  Your
> data is not centered on Greenwich - but the error message is trying to
> say that you can shift your grid (with the shiftgrid function) so that
> is has the same orientation as the map projection region.  This only
> comes into play with global projections that 'wrap-around' at the edges,
> like the mollweide and mercator projections.  The orthographic
> projection does not 'wrap around' - hence you don't get the error message.

Looking at the shiftmap function it looks like I should shift the
co-ordinate grid so that my longitude runs from -180 to 180 instead of
0 to 360, therefore the following shiftgrid call should do this

values, lon = basemap.shiftgrid(180, values, lon)

However I still get the same error and the corruption in the resulting
plot.  I feel like I'm missing something obvious here but can't find
it.

Cheers

Adam

On 11/10/2007, Jeff Whitaker <js...@fa...> wrote:

> Adam:  I assume your data is on a latitude-longitude grid?  You've asked
> for a mollweide projection centered on the Greenwich meridian.  Your
> data is not centered on Greenwich - but the error message is trying to
> say that you can shift your grid (with the shiftgrid function) so that
> is has the same orientation as the map projection region.  This only
> comes into play with global projections that 'wrap-around' at the edges,
> like the mollweide and mercator projections.  The orthographic
> projection does not 'wrap around' - hence you don't get the error message.

Thanks, that makes sense now.

Cheers

Adam

Adam Mercer wrote:
> Hi
>
> I'm running into a problem using the mollweide projection, with the
> following simplified code, my actual code doesn't use random data for
> values but this is a clearer example to the problem I'm experiencing:
>
> lon = numpy.arange(0, 361, 1)
> lat = numpy.arange(-90, 91, 1)
> x, y = numpy.meshgrid(lon, lat)
> values = numpy.random.random((181, 361))
>
> map = basemap.Basemap(projection='moll', lon_0=0, resolution='c')
> map.drawcoastlines()
> map.drawcountries()
> map.drawmapboundary()
> map.drawmeridians(numpy.arange(0,360,30))
> map.drawparallels(numpy.arange(-90,90,30))
>
> X, Y = map(x, y)
>
> map.contourf(X, Y, values)
>
> I get the following error:
>
>  WARNING: x coordinate not montonically increasing - contour plot
>  may not be what you expect.  If it looks odd, your can either
>  adjust the map projection region to be consistent with your data, or
>  (if your data is on a global lat/lon grid) use the shiftgrid
>  function to adjust the data to be consistent with the map projection
>  region (see examples/contour_demo.py).
>
> And the resulting map is incorrect due to the horizontal trends, see
> http://tier2.ihepa.ufl.edu/~ram/files/moll.jpg
>
>
> but if I use the orthographic projection ie:
>
> map = basemap.Basemap(projection='ortho', lat_0=-20, lon_0=-30, resolution='c')
>
> Then there are no errors, and the map is displayed as expected, see
> http://tier2.ihepa.ufl.edu/~ram/files/ortho.jpg
>
> I am unsure as to why I am receiving this error for the mollweide
> projection, as my coordinate grid is covering the entire surface.  I
> am clearly doing something wring here but I don't know what - does
> anyone know what is causing this issue?
>
> Cheers
>
> Adam
>   

Adam:  I assume your data is on a latitude-longitude grid?  You've asked 
for a mollweide projection centered on the Greenwich meridian.  Your 
data is not centered on Greenwich - but the error message is trying to 
say that you can shift your grid (with the shiftgrid function) so that 
is has the same orientation as the map projection region.  This only 
comes into play with global projections that 'wrap-around' at the edges, 
like the mollweide and mercator projections.  The orthographic 
projection does not 'wrap around' - hence you don't get the error message.


-Jeff

-- 
Jeffrey S. Whitaker         Phone  : (303)497-6313
Meteorologist               FAX    : (303)497-6449
NOAA/OAR/PSD  R/PSD1        Email  : Jef...@no...
325 Broadway                Office : Skaggs Research Cntr 1D-124
Boulder, CO, USA 80303-3328 Web    : http://tinyurl.com/5telg

=0AI i have tree lists or array of values=0Alist x of 100... values=0Alist =
y of 100.. values=0Alist mag of 100.. values=0Alist x and y are coordiantes=
 of points =0Aand list Mag is magnitude of something at that point=0A=0Ahow=
 can i plot this quantities using matplotlib, any function please?=0A=0Amy =
code starts as.....i need to plot the points vhat can i use?=0A=0Afrom __fu=
ture__ import division=0Afrom matplotlib.patches import Patch=0Afrom pylab =
import *=0A=0Adef func3(x,y):=0A    return (1- x/2 + x**5 + y**3)*exp(-x**2=
-y**2)=0A=0A=0A# make these smaller to increase the resolution=0Adx, dy =3D=
 0.5, 0.5=0A=0AX =3D arange(-3.0, 3.0001, dx)=0A=0AY =3D arange(-3.0, 3.000=
1, dy)=0A=0AMag=3D X**2+Y**2=0A=0A?????(X, Y, Mag)=0Acolorbar()=0Aaxis([-3,=
3,-3,3])=0Asavefig('three d plot of points making a surface')=0Ashow()=0A=
=0A=0A=0A=0A=0A=0A      =0A=A1S=E9 un mejor ambientalista!=0AEncuentra cons=
ejos para cuidar el lugar donde vivimos en:=0A=0Ahttp://telemundo.yahoo.com=
/promos/mejorambientalista.html=0A=0A=0A=0A=0A=0A      ____________________=
________________________________________________________________=0A=A1S=E9 =
un mejor fot=F3grafo!=0APerfecciona tu t=E9cnica y encuentra las mejores fo=
tos.                       =0Ahttp://telemundo.yahoo.com/promos/mejorfotogr=
afo.html

>
> Can this be changed?  Is there a better approach I should take in
> getting my students started using scipy and pylab together?
>

Teaching them what is a module and a namespace is a good think, why don't
telling them to do :

import pylab as pl
import numpy as npy

for instance so that they have a feeling it's almost like MAtlab, but better
structured ?

Matthieu

Hi,

I'm using matplotlib in a C++ app (with a qt4 gui), by embedding python with
boost::python. The C++ app calls Py_Initialize(), init_myplottingmodule(), and
boost::python::import("matplotlib.pylab") once on startup and certain GUI
events then fire up a matplotlib window via calls like this one:

// simplified version
void plotCurve(){
    clf();
    title("Diagonal line plot");
    double O1[] = {0,1};
    plot(std::vector<double>(O1,O1+2), std::vector<double>(O1,O1+2), "b:");
    show();
}

Although this does sort of work, it doesn't work quite right. Specifically on
clicking on the close button of the window, bad things frequently happen. For
example, the first close seems to work, but subsequent attempts to close newly
opened plots just zombify the window (it no longer repaints automatically but
stays open; replots happen to that same window, i.e. the one that was opened
second).

Now I'm somewhat aware of all the nastiness of different event loops, the
heroic efforts of ipython to make matplotlib work nicely interactively without
blocking the REPL, but somehow I would have (naively) thought that all that
work was just needed to avoid blocking. For the code above, blocking till the
window would be closed is perfectly fine. Indeed that's what happens if I try
something equivalent in the plain python shell (outside the C++ app).

Any idea about the likely cause of the problem and what might be the simplest
way to get it to work as expected (similar symptoms appear w/ matplotlib
0.87.7 and 0.91 under linux and osx)?

cheers,

'as

Hi

I'm running into a problem using the mollweide projection, with the
following simplified code, my actual code doesn't use random data for
values but this is a clearer example to the problem I'm experiencing:

lon = numpy.arange(0, 361, 1)
lat = numpy.arange(-90, 91, 1)
x, y = numpy.meshgrid(lon, lat)
values = numpy.random.random((181, 361))

map = basemap.Basemap(projection='moll', lon_0=0, resolution='c')
map.drawcoastlines()
map.drawcountries()
map.drawmapboundary()
map.drawmeridians(numpy.arange(0,360,30))
map.drawparallels(numpy.arange(-90,90,30))

X, Y = map(x, y)

map.contourf(X, Y, values)

I get the following error:

 WARNING: x coordinate not montonically increasing - contour plot
 may not be what you expect.  If it looks odd, your can either
 adjust the map projection region to be consistent with your data, or
 (if your data is on a global lat/lon grid) use the shiftgrid
 function to adjust the data to be consistent with the map projection
 region (see examples/contour_demo.py).

And the resulting map is incorrect due to the horizontal trends, see
http://tier2.ihepa.ufl.edu/~ram/files/moll.jpg


but if I use the orthographic projection ie:

map = basemap.Basemap(projection='ortho', lat_0=-20, lon_0=-30, resolution='c')

Then there are no errors, and the map is displayed as expected, see
http://tier2.ihepa.ufl.edu/~ram/files/ortho.jpg

I am unsure as to why I am receiving this error for the mollweide
projection, as my coordinate grid is covering the entire surface.  I
am clearly doing something wring here but I don't know what - does
anyone know what is causing this issue?

Cheers

Adam

On 10/11/07, Ryan Krauss <rya...@gm...> wrote:

> Can this be changed?  Is there a better approach I should take in
> getting my students started using scipy and pylab together?

Yes, this was left in initially for backward compatibility but I think
we should strive for maximal numpy compatibility going forward.  In
svn, we now have pyplot ehich is like pylab but minus the numpy stuff.
 Thus if you are using svn (or future releases) you can encourage your
students to

from scipy import *
from matplotlib.pyplot import *

I have successfully (I think) coerced my students into using
Scipy/Numpy for signal processing and dynamic system modeling.  They
are mechanical engineering coming from a Matlab background.  In order
to make using Python easy and have it feel like Matlab,  I teach them
to put

from scipy import *
from pylab import *

at the beginning of every script.  One problem with this is that the
zeros and ones functions of pylab default to integers while those from
scipy default to floating point numbers.  I have had several students
this week beating there heads against problems that turned out to be
trying to put floating point values in an array that was created using
pylab.zeros.

Can this be changed?  Is there a better approach I should take in
getting my students started using scipy and pylab together?

Thanks,

Ryan