| Re: Reding data into IDL [message #8793] |
Mon, 21 April 1997 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Richard Hall writes:
> I have a set of co-ordinates (lat,long) containing ca. 800 points.
> I wish to plot these points on a map. My problem is,
> how do I convert the ascii file into a format understood by IDL?
The nice thing about IDL is that no conversion is necessary. This
data is ready to go! Suppose you have 2 columns by 800 rows of
data. Read the ASCII data like this:
data = FltArr(2, 800)
OPENR, lun, filename, /Get_Lun
READF, lun, data
FREE_LUN, lun
lat = REFORM(data(0,*))
lon = REFORM(data(1,*))
If you want to plot these points on a map, you can do it directly
with a routine like PLOTS. If the points are in lat/lon coordinates
nothing needs to be done except to establish a map projection.
For example,
Map_Set, /Orthographic, /Isotropic
PLOTS, lon, lat, PSYM=4
If you wish to plot these points on a map as an image or contour
plot, then you will need to grid the points into a 2D array using
the TRIANGULATE and TRIGRID routines. There is an excellent
article on how to do this in the Map Projection Tips section
of my web page.
> Also, the map data supplied with IDl is a little to coarse for my
requirements.
> How do I go about obtaining a finer set of co-ordinates, and loading them
into
> IDL.
Go back to your installation CD ROM and download the high resolution
CIA database.
Cheers!
David
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
2642 Bradbury Court, Fort Collins, CO 80521
Phone: 970-221-0438 Fax: 970-221-4762
E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com
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