Information request

in fact the points are not in a rectangular array and pixels are missing, like you said

I'll put the code and binary file online tomorrow as I have not access to it today, but reading it is not the problem

when read, the values are in three arrays of same size, which I will have to convert to a 2D masked array... we'll see tomorrow if I have succeeded

many thanks


Antoine De Pauw wrote:

Thanks Jeff,

In fact my points are arranged in three unsorted arrays, with a simple scheme (thats why I couldn't plot them with imshow and others)


[-10][ 17][0.3]
[ 37][ 23][3.7]
... ... ...

and so for many rows...

what I have to do is looping through my arrays like that

while i < rowcount:

it is evidently an idea of how it could be done easily but my knowledge of these libraries is too weak for me to figure out how to do it

my data comes from huge binary files but is extremely simple, so it would be really easy for anyone to help me as the problem itself is how to put unsorted points on the map with latitude and longitude coordinates

Antoine: You haven't said if your data forms a rectangular array. If
so, you can build a 2-d array from the input file and plot it with
imshow. If not, you can still plug the elements into a 2-d masked
array, leaving the missing pixels masked. You say the points are
'unsorted', does that mean they are randomly distributed and do not form
a rectangular grid?

It would really be much easier to help if you gave us more information,
such as how the data is structured, what the pixel footprint is, etc.
Perhaps you could post the binary file on an ftp site somewhere with
code to read it.

Also, please hit 'reply all' when replying, so the matplotlib users
mailing list is CC'ed.


Antoine De Pauw wrote:


I'm sorry, as english is not my mothertongue and it is sometimes difficult to be understandable.

All is in the script I gave to you initially, except the point drawing code which would be useless as it is proven not to work (I dont know the method to do it).

What I have is a map, and a set of pixels I have to put on it with geographic coordinates.

I cannot find the right method to put colour pixels on the map, that's the problem.

I have that map in miller projection, and three arrays containing respectively latitude, longitude and satellite measured value.

What I need to obtain is something approximately like this: but with the basemap toolkit.

So, my question is: how could I do to plot a coloured pixel at coordinates lat:lon on that map? If I have just the method to project a geographic coordinate on the map and put a coloured pixel at the right place, all is done and I just have to loop my arrays... Also, I would have to implement some antialiasing on the map.


Are the pixels arranged on a regular grid - or are they randomly
distributed? If they are on a grid, it's easy (using pcolor or imshow)

If you could send me your data I may be able to get you started.

(I'm cc'ing the matplotlib list so others can join in the discussion).


If this is not possible to do it in a simple and explainable way, please tell me and I'll continue using matlab or searching for the bit of code which will save me

Anyway, I have to thank you for your interest to help me..

Many thanks,

Antoine De Pauw

Antoine De Pauw wrote:

Hi, and thanks for the answer

In fact, what I do is reading a binary file to obtain 3 arrays (Lat,Lon,Val) describing geographic points which are associated by index (like point 1 is Lat[0]:Lon[0] with value Val[0])

What I need to do is to plot some points on the map (miller projection for most) based on latitude and longitude, to obtain a colour map (points are unordered, it is from IASI satellite computations)

I'm able to create a map, draw simple things on it, etc but the problem I have is any method I try for plotting points is failing, either pcolor, pcolormesh, imshow, etc.

When I found your post on that mailing list, I figured out that you might have the experience and skills to easily explain to me how to manipulate these points and plot them on the map, as there's like no help on the web except standard examples...

Please tell me if this is possible for you to give me some tips, or if it takes too much of your time just advice me some lectures

Best regards,

De Pauw Antoine

Antoine: It would really help to have a script demonstrating your
problem. It sounds to me like you want to plot markers representing a
set of points - for that you should use the scatter method. pcolor,
pcolormesh and friends are for plotting gridded data.


De Pauw Antoine wrote:

Dear sir,

I&#8217;m currently trying to improve our plotting tools here at the &#8220;Quantum
Chemistry and Photophysics&#8221; section of the Université Libre de
Bruxelles, and I ran, after many time passed at searching for a
solution, on an explanation from you here:

It seems that you could help me find a solution, as I cannot plot any
points on maps.

Could you please tell me what I could do to plot data in a simple way,
assuming I have 3 unordered arrays containing respectively latitude,
longitude and values to plot?

Some tips would be very nice from you as any method I have tried so far
give me some errors&#8230;

Thank you very much in advance,

Best regards,

PS: I give you the code I&#8217;m using currently, missing the plotting part

from mpl_toolkits.basemap import Basemap

from numpy import *

from import fread

import matplotlib.pyplot as plt

import numpy as np

import os

import sys

import array


print('preparing map')

map =



labels=np.arange(-180,180,60), labelstyle="+/-")

#map.drawparallels(np.arange(-90,90,30), linewidth=0.5,
labels=np.arange(-180,180,30), labelstyle="+/-")

print('reading binary data')









print('shifting latitudes and projecting to map')


while i < nbreligne:






print('plotting data')

#plotting code comes here

Antoine: If you send me a self-contained script that produces the
problem you see, I can help you debug it. As it stands now, I have very
little to work with - it could be your plotting commands, or it could be
your data.


print('saving map')



*Antoine De Pauw*
Collaborateur de recherches, Informatique - Research collaborator, IT
Laboratoire de chimie quantique et photophysique - Quantum chemistry and
photophysics laboratory
*Université Libre de Bruxelles - ULB <;\*

Jeffrey S. Whitaker Phone : (303)497-6313
Meteorologist FAX : (303)497-6449
NOAA/OAR/PSD R/PSD1 Email : Jeffrey.S.Whitaker@...259...
325 Broadway Office : Skaggs Research Cntr 1D-113
Boulder, CO, USA 80303-3328 Web : Jeffrey S. Whitaker: NOAA Physical Sciences Laboratory

Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328

Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328

Jeffrey S. Whitaker Phone : (303)497-6313
Meteorologist FAX : (303)497-6449
NOAA/OAR/PSD R/PSD1 Email : Jeffrey.S.Whitaker@...259...
325 Broadway Office : Skaggs Research Cntr 1D-113
Boulder, CO, USA 80303-3328 Web : Jeffrey S. Whitaker: NOAA Physical Sciences Laboratory