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Hi Ansley,
Thanks a lot, it works fine! Now, some
data are over land and they are NaN values indeed. According to
"Setting a missing value" at Ferret FAQ having an ocean mask with earth's
surface may help to get only data over ocean, Where could I find an ocean mask with earth's surface at 0.2 minute resolution?
Cheers
Arturo
----- Original Message -----
Sent: Tuesday, February 16, 2010 1:29
PM
Subject: Re: [ferret_users] Reading
variables from an ascii file
Hi Arturo-
It might be helpful for your C program to add
the longitude and latitude values in each line so it's easier to see what
you're doing, but that's not strictly necessary. So, the second and third
columns would be lat and lon - but read on and see if you think this is
necessary -
19600101000000 18.05000 271.94998 7.2 278. 0.26
1.34 0.72 0.88 5.73 4.50 3.99 3.64 255.
26. ...
19600101010000 18.05000 271.94998 7.2 278. 0.26 1.34
0.72 0.88 5.73 4.50 3.99 3.64 255. 26.
...
19601231230000 18.05000 271.94998 7.2 278. 0.26 1.34
0.72 0.88 5.73 4.50 3.99 3.64 255.
26.
19600101000000 18.05000 272.1500 7.2 278. 0.26 1.34
0.72 0.88 5.73 4.50 3.99 3.64 255.
26.
19600101010000 18.05000 272.1500 7.2 278. 0.26 1.34
0.72 0.88 5.73 4.50 3.99 3.64 255.
26.
...
19601231230000 18.05000 272.1500 7.2 278.
0.26 1.34 0.72 0.88 5.73 4.50 3.99 3.64
255. 26.
Is time listed as
each hour of the year? If so you should be able to read the data in a
way similar to the ASCII reading Examples 6 and 7 (see "ASCII data, reading,
examples" in the Users Guide Index). Time is varying fastest, then
Longitude, then Latitude, correct?
So, first just learning how to read
one variable. I'll just make up some example longitude and latitude
axes; you'll adjust these to match your data. They don't have to be regularly
spaced, but we are assuming they're on a grid.
There are several ways
to define coordinate axes - see the documentation.
DEFINE AXIS/X=271.95:279.0:0.2/UNITS=degrees_lon xaxis
DEFINE AXIS/Y=18.05:19.0:0.05/UNITS=degrees_lat yaxis
DEFINE
AXIS/T="1-jan-1960:00:00":"31-Dec-1960:23:00":1/UNITS=hours taxis
DEFINE
GRID/X=xaxis/Y=yaxis/T=taxis
xytgrid
FILE/var="tvar,v1"/grid=xytgrid/order=txy
file.dat
I'm assuming the data looks like this - without
the lon and lat variables I talked about at the start of this
message.
19600101000000 7.2 278. 0.26 1.34 0.72
0.88 5.73 4.50 3.99 3.64 255. 26.
0.67 4.74 3.68 3.34 3.09 271. 21.
0.58 5.73 5.59 5.38 5.22 236.
19.
19600101010000 7.2 278. 0.26 1.34 0.72
0.88 5.73 4.50 3.99 3.64 255. 26.
0.67 4.74 3.68 3.34 3.09 271. 21.
0.58 5.73 5.59 5.38 5.22 236.
19.
...
19601231230000 7.2 278. 0.26 1.34 0.72
0.88 5.73 4.50 3.99 3.64 255. 26.
0.67 4.74 3.68 3.34 3.09 271. 21.
0.58 5.73 5.59 5.38 5.22 236.
19.
If you do put the lon and lat data into the
file, then you'd read it with FILE/var="tvar,xvar,yvar,v1"/...
This
will read the time variable into "tvar" which you can just ignore, because it
contains information that's already captured in the definition of the time
axis. Then the variable whose value as listed in your examples as 7.2 will be
v1. Try this, and look at your variable in Ferret (do some commands like
SHADE at a particular time, or plot a time series at a single XY location and
see if it looks correct.)
Now you can read more variables. A
detail here is that Ferret will only read 20 variables from an ASCII
file. I count 26 in your example. So if you try
yes?
file/var="tvar,v1,v2,v3,v4,v5,v6,v7,v8,v9,v10,v11,v12,v13,v14,v15,v16,v17,v18,v19,v20,v21,v22,v23,v24,v25,v26"/grid=xytgrid
file.dat
you'll get an error message. To get around
that you might do this - probably naming your variables with meaningful
names -
yes?
file/var="tvar,v2,v3,v4,v5,v6,v7,v8,v9,v10,v11,v12,v13,v14,v15"/grid=xytgrid
file.dat
yes? save/clobber/file=my_data.nc
v1,v2,v3,v4,v5,v6,v7,v8,v9,v10,v11,v12,v13,v14,v15,v16,v17,v18,v19
yes?
cancel data file.dat
yes?
file/var="v20,v21,v22,v23,v24,v25,v26"/grid=xytgrid/format=(99x,F6.2,...)
file.dat
yes? save/append/file=my_data.nc
20,v21,v22,v23,v24,v25,v26
where the FORMAT statement
would specify the Fortran format for the remaining variables to be read
in.
Hope this gets you started!
Ansley
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