Beyond the Mouse LAB 5: MATLAB I/O 1
September 26, 87
Instructor: Jeff Freymueller
x7286 Elvey 413B jfreymueller@alaska.eduTA: Shanshan Li
Last Updated: September 12, 2017
Due: Tuesday Oct 3, before class
Lab slides
NONE.
Exercise 1:
Download the file FAIR.pfiles.txt and open it in a text editor (could be Matlab's editor) to have a look at it. It's again a file that contains daily positioning solutions for the continuous GPS site FAIR. This is a more or less typical text file, the sort will likely cross your path at some point in your future. There's one header line documenting the meaning of the columns, a bunch of columns and many, many rows of data. Here's again what the columns mean:
epoch (decimal year) | GPS Site | Tie Site | Longitude (deg) | Latitude (deg) | Height (m) | Sigma_east (mm) | Sigma_north (mm) | Sigma_vert (mm) | cov_en | cov_eu | cov_nu | path to solution file
Your job is it to write a script that reads the whole file. Skip the one headerline by setting the right
parameter-value-pair (read the documentation!) -- you are not allowed to
remove it manually from the data file! Then your script will write the columns epoch, lon, lat, and height into
a new file FAIR2.dat. Once this works add the site 'FAIR2' to your station definition
cell array from the lab 04 and run the script to plot the data. It should be fairly similar to
station FAIR in the vertical. The latitude and longitude trends will be different because
the reference for velocities is different -- the files we gave you earlier had the motion
of the North American plate removed.
The purpose of this exercise is in having you figure out what format strings to use, how to put one together, and to decide which function to use for reading and writing your data. Plus some documentation reading.
Exercise 2:
Take the script you've just written and turn it into a function decimate_data
that has two parameters, the name of the input data file and the desired name of the output
file. There is no need for a return value here. Adapt your code from the script such that
it uses these parameters rather than operating on hardcoded file names. Then write a
script that calls decimate_data for FAIR.pfiles and creates
FAIR2.dat. I encourage you to use try-catch to make sure your
code does not just crash when a file does not exist.
Summary questions
(no need to implement these, think about them and write out your answers)
Assume your plotting routine from LAB 04 remains stable, but the respective station data you want to
display will vary. What would be a reasonable step to avoid having to edit the gps_station cell
array at the beginning of your script every time the stations you want to display change, AND you don't want to display
all available stations, but only a subset of them? For example, if you want
to read and plot only the ones that you have not made plots for already?
Now assume your data lives in different directories. How could your change your solution for LAB04 to accomodate such distributed data? Hint: Think back to the part of the solution for the flow chart problem from Lecture 1 and 2 that dealt with lecture number and dates.
Stuff to turn in (I recommend sending in an archive):
- all files for Exercise 1 (that includes the updated files from lab04, and the output figure!)
- all files for Exercise 2
- yes, I want the script AND the function solution
- written text for the summary questions
Helpful Matlab Functions:
Here is a list of functions that might be of help.
textread: read a text filetextscan: read a text file differentlyimportdata: import data from text files or imagesfopen: open a filefclose: close a filefprintf: print to a file
Dr. Jeffrey T. Freymueller
Professor of Geophysics
Geophysical Institute
University of Alaska, Fairbanks
Fairbanks, AK 99775-7320