Tutorial GAMIT part 1

This example is discuss about GPS data processing using GAMIT/GLOBK

The example is set up to :

A. Conduct phase processing (sh_gamit).

B. Compute and plot daily repeatabilities (sh_glred).

So please note that this tutorial is only talked about phase processing using sh_gamit and compute daily repeatability using sh_glred, this tutorial is not (yet) talked about combine daily result using GLOBK processing.

As I said, using this tutorial will yield daily position of your data processing. Even your input rinex is multiple day, the command will generate daily .org file. Then, you can combine this daily result on one file repeatability using GLOBK (will be publish soon) (^_^)v.

enjoy!

–Begin Processing–

1. CREATE PROJECT DIRECTORY FOLDER.

You can done this work manually or by terminal typing on the path where you will work on GAMIT (e.g= Using, mkdir [your project]). Please note that the name of your project must be named with only 4 digit.

2. CREATE GPS DATA, IGS, and BRDC FOLDER.

Just same as before, just create folder and use “rinex”, “igs”, “brdc” as the name for the folder.

a. Rinex data.

Store your GPS data observation in this folder. If you wanna use RINEX from IGS station, you can download easily using GAMIT scritp named “sh_get_rinex”. just type in your terminal “sh_get_rinex -archive sopac cddis -yr [years] -doy [doy] -ndays [days] -sites [IGS sites]”

Noted:

  • years: 4 char year of nav data requested
  • doy: 3 char day of year of nav data requested
  • days: Number of consecutive days of data to retrieve
  • IGS sites: List of sites to be retrieved from the ftp archive (IGS websites)

3. INPUT DATA
firstly, set up GAMIT data environment using “sh_setup” command. Type the command on the terminal under your project folder.
e.g: “sh_setup -yr [year] -apr [itrf]

Noted:

  • year: 4 char year of observation
  • itrf: ITRF that will used on processing

4. ESTABLISH INPUT FILE

Input files provided in advance are lfile, sistbl, sestbl, station.info, process default. Copy and edit those file from gg/tables to directory tables under your project folder.

  • lfile: input the coordinates apriory as initial coordinates (user can use coordinates from RINEX header).
  • sittbl: listed IGS stations used by GAMIT to compute loose constrained solution.
  • sestbl: list and setting of parameters used on GAMIT computation
  • station.info: contain all information related to station that will used on the processing.
  • process.default: file which contain the default process setting.
  • sites.default: file used for controlling the use of station in the processing.
*User is strongly recommended to read GAMIT/GLOBK manual book to make modification of those input file.

 5. AUTOMATIC BATCH PROCESSING (SH_GAMIT)

type

sh_gamit -s [year] d1 d2 -expt [expt] -pres [ress]

e.g: sh_gamit –s 2011 164 167 –expt regi -pres ELEV

noted:

  • -s d1 d2: where d1 is start day and d2 is stop day to be processed. e.g: 2011 164 167
  • -expt: 4 char name of experiment/s to run (check on your input file)
  • -pres: Plot gamit residuals as skyplots. Option: NO / YES (skyplot only) / ELEV (skyplot + phase vs elevation [Default N].

6. SH_GAMIT OUTPUT

Check the summary for number of stations, Postfit RMS , Postfit nrms, ambiguity resolution, and coordinate adjustments in your <doy> folder under your project directory. Look at the sky plots and phase vs elevation angle plots in the /gifs directory. If necessary, compare the q-files and sky plots with those in the check_files directory (Note that the sky plots in check_files are still in postscript, whereas those in /gifs have been converted to gif images.)

fig 1. phase vs elevation angle plot

fig 2. Sky plot

7. SH_GLRED

before start to use sh_glred, user must get template command files into /gsoln by typing (on the terminal) at the project level “sh_glred -cmd

go to /gsoln directory under your project directory, edit globk_comb.cmd and glorg_comb.cmd to use translation-only stabilization, and to use for stablization the apr file and  stab_site list pre-generated for the example.

In globk_comb.cmd, comment out (add a character to column 1, user can put ‘x’ character)

apr_wob 10 10 0 0
apr_ut1 10 0

and uncomment (remove the ‘x’)

x apr_wob .25 .25 .1 .1
x apr ut1 .25 .1

In glorg_comb.cmd, comment out

pos_org xtran ytran ztran xrot yrot zrot
source ../tables/[stab_site.file]

and uncomment (remove the ‘x’)

x pos_org xtran ytran ztran
x source ../../tables/regional_stab_site

*please note, the user must copy [stab_site.file] from gg/tables to tables under the project directory. User can choose stab_site file that will use on the processing. Just make sure for change [stab_site.file] into stab_site name that will used in the processing.

After establishing path and other important file, then type on the terminal:

sh_glred -d [yr day] -s [yr1 d1 yr2 d2]  -expt [expt] -opt H G E LA

-s <yr1 d1 yr2 d2>:   start and stop dates, e.g. -s 2011 164 2011 167

-expt: 4 char name of experiment/s to run.

-opt: Optional input to set some output paramater.

H: Run htoglb on all ascii files present or linked within glfpth (usually procdir/glbf).

G: Run glred for combination or repeatabilities.

E: Run ensum and sh_baseline for plots

LA: call h-files from global global that locally store on your local directory.

*noted: for advance setting, please read GAMIT/GLOBK manual book.

8. SH_GLRED OUTPUT

The script as commanded will translate the GAMIT ascii h-files in each day directory to GLOBK binary h-files and put them into the /glbf directory ( H ); create a gdl file for each day listing the h-file; run GLOBK for each day ( G ) using globk_comb.cmd and glorg_comb.cmd ( G ); and generate time series plots ( E, from program ensum).

In /gsoln, use Ghostscript (‘gs’) to view the time series, which should show wrms repeatabilities at the level of 1 mm horizontal and 2 mm vertical, and nrms values < 1.0. If these are good, there is usually no need to inspect any other files.

Please don’t be hesitate to ask me if you face some difficulties on the processing.

-to be continued (insyaallah, for GLOBK processing).

Kyoto, 3 May 2014

Hidayat Panuntun

 

Tutorial GAMIT part 2

This article is continuing on GPS data processing using GAMIT. For reader who want to read previous article, please read this. Assumed […]

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