Re: [Matplotlib-users] plotting points/locations from data file

[Michael R. <raw...@ya...>]

Sorry I should have mentioned that longitudes are negative; there is a '-' before each longitude, like so:

39.4670  -76.1670 
46.4000  -74.7670 
45.3830  -75.7170 
43.6170  -79.3830 
45.5170  -73.4170 


Also the plt.text line you sent had lon[i] rather than lons[i].  I corrected that and changed my longitudes to not have the '-' sign and the code ran without error. Could the '-' be causing a problem?  I need to input the lat, lon as in the file as shown above.

Mike

--- On Tue, 4/19/11, Ian Bell <ib...@pu...> wrote:

From: Ian Bell <ib...@pu...>
Subject: Re: [Matplotlib-users] plotting points/locations from data file
To: "Michael Rawlins" <raw...@ya...>
Cc: Mat...@li...
Date: Tuesday, April 19, 2011, 7:22 PM

If you want to plot a given marker at the point, for instance a circle, replace the last line of my code plt.text...... with 

plt.plot(lats,lons,'o')

for a circle, or 

plt.plot(lats,lons,'s')



for a square.  Refer to Plot for more information on the markers you can use.  You are getting the error because you have a delimiter different than a single space, so it isn't splitting the line.  Replace ' '  in the split command with your whitespace delimiter.  Is it a tab? Then you want '\t' .



Good luck,
Ian

----
Ian Bell
Graduate Research Assistant
Herrick Labs
Purdue University
email: ib...@pu...
cell: (607)227-7626



On Tue, Apr 19, 2011 at 7:14 PM, Michael Rawlins <raw...@ya...> wrote:



Yes, there is whitespace between each lat and lon on each line.  But, actually, I'd simply like to plot a dot at each location.  The '1' was there in my example because I do not yet know how to plot a particular symbol.  Here is what I got when I tried the code you just suggested. 



Traceback (most recent call last):
  File "test.py", line 319, in <module>
    (lat,lon)=line.strip().split(' ')
ValueError: too many values to unpack




There are 203 records in the data file.  Line 319 of test.py is this:

(lat,lon)=line.strip().split(' ')


--- On Tue, 4/19/11, Ian Bell <ib...@pu...> wrote:



From: Ian Bell <ib...@pu...>
Subject: Re:
 [Matplotlib-users] plotting points/locations from data file
To: "Michael Rawlins" <raw...@ya...>
Cc: Mat...@li...


Date: Tuesday, April 19, 2011, 6:52 PM

To clarify, you are trying to read in a set of (lat,lon) points in a file that is space delimited, store the data, and then put a text marker at each point, with each point numbered in order?  The critical part is that you want to use a list (or numpy array) instead of a dictionary.  Something like this ought to do (don't have MPL on this computer though - pretty sure this should work):





lines=open('file.txt','r').readlines()
(lats,lons)=([],[])
for line in lines:
    (lat,lon)=line.strip().split(' ')
    lats.append(float(lat))
    lons.append(float(lon))





for i in range(len(lons)):
    plt.text(lats[i],lon[i],str(i+1),ha='center',va='center',color='white')

I'm sure there are a bunch of more compact ways to do this, but this should work.





Ian
----
Ian Bell
Graduate Research Assistant
Herrick Labs
Purdue University
email: ib...@pu...


cell: (607)227-7626



On Tue, Apr 19, 2011 at 4:09 PM, Michael Rawlins <raw...@ya...> wrote:






I'm trying to plot a series of points/locations on a map. I'm reading the latitudes and longitudes from a file, with each lat, lon pair on each record (line).  Here is the code:



def make_float(line):

    lati, longi = line.split()

    return float(lati), float(longi)



my_dict = {}

with open("file.txt") as f:

    for item in f:

        lati,longi = make_float(item)

        my_dict[lati] = longi



xpt,ypt = m(-76.1670,39.4670 )

plt.text(xpt,ypt,'1',color='white')



#print my_dict



The matplotlib code which I've previously used to plot a single point on the map is below, with longitude and latitude in ( ):



xpt,ypt = m(-70.758392,42.960445)

plt.text(xpt,ypt,'1',color='white')



When replacing (-70.758392,42.960445) with (longi,lati), the code plots only a single '1' at the location of just the last coordinate pair in the file. So now I only need to plot them all. Does the code I've implemented have an implicit loop to it?







Mike







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