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UNAVCO IDV: GPS Data -- Time Series, Velocity Vectors, and Error Ellipses

The UNAVCO IDV can display GPS velocity vectors and error ellipses, and overlay the velocity plots on other geophysical data such as surface maps and 3D topographic relief. The IDV can also display time series of GPS station position displacements (north, east and vertical components, and their error estimates with time).

GPS velocity vector data may have 2 components (east and north), or 3 components including vertical, and in that case the IDV will plot GPS vectors in 3D. An overhead map view will show only the horizontal vector in either case.

(To show velocities vectors, your copy of the IDV must use a "UNAVCO IDV plugin" made March 24, 2009 or later.


Put Your GPS Velocity Data in the IDV

click for full size

Look at this sample GPS velocity vector data file for the IDV. Each line is one station's values. The values are separated with commas. This data format allows plots of velocity vectors (from ve,vn) and error ellipses (from sigx,sigy,corrxy), The IDV requires time and altitude for each observation and in this example those values are are set to one time and one altitude (0); note the time format. There is a 4-character station label at the end of each data row.

Alternately, time and altitude can be shown in each data row in the correct order position. There is no vertical velocity value in the first example; add a new item "vz[unit="mm yr-1"]" if you need vertical. This sample data file includes time, altitude, and vertical motion components at each station, but no station id. vz downwards is negative. Time is defined to seconds.

The tail is the station location since for crustal motion the interest is where a point is headed, not where it went. The UNAVCO IDV layout models put the station id at the station location, if a station id is supplied. See this example display.

Put your data in a file with one of these formats. Keep the filename extension 'csv.' For more about this file format for the IDV, see the Unidata IDV User's Guide: Text (ASCII) Point Data Format.. For best use of the IDV, all variables need unit names. For recognized names of units use the UD units and see Supported Units.

Time is required by this format, but you can of course use any time you like, including a dummy or placeholder value. Tine is used by the IDV to merge separate data sources at one time in one plot, or for time animation.

Making a Display

Load your data file in the IDV with the Dashboard window, Data Choosers -> Files, and find your file. Click on "Add Source."

In the dashboard "Fields" panel in the center, click on "Point Data." For "Layout model," choose one of the "GPS vectors" choices provided by the IDV (the IDV has no vectors). Click on "Create Display." Note that in the overhead view (CTRL-R) you cannot see the vertical component of velocity.

You can control vector length scaling, using the "Scale" entry box in the Display control window that pops up when the display is made. The Declutter check box reduces the number of symbols in the display. Read more about Point data plots and Working with the Point data Plot Symbols using "Layouts Models". To zoom, pan, and rotate see Zoom, pan and rotate. See also Making GPS Displays - More Details.

Here is an IDV bundle file that should make a GPS display in your IDV after you add the new IDV plugin. It uses the sample data file shown above. Load it with the URLs window in the Data Choosers.


PBO GPS Velocities


    UNAVCO IDV display of PBO GPS velocities, USGS surface fault lines, and JPL "Blue Marble" satellite image.
    Click to see full size.

    Original Data Source:
    The sources for the GPS velocity data for the PBO and co-processed stations, the combined products from the GPS Analysis Center at MIT, are online at:

    A PBO "pbo.final_frame.csv" data file with a modified header for UNAVCO IDV use is here: pbo_final_frame.csv.

    To load this data source into the IDV, just copy the link location (URL); you do not need to download the file. Enter the URL in the URLs entry box in the IDV Dashboard's "Data Choosers" window. Click on Add Source. In the dashboard "Fields" panel in the center, click on "Point Data." For "Layout model," choose "GPS vectors"(black or red). Click on "Create Display." to make a "Text Point Data" display. Change the "Location Model" (in the display control) "GPS velocity vectors" (red or black). In the display control for the "Text Point Data" display, click on the "Times" tab, click on "Show: Multiple" to see all data times in one display. To declutter (see all vectors), in the "Layout" tab, click off the "Declutter" check box.

    click for full size


PBO GPS Station Time Series


GPS Vel 1.0 ITRF 2000" Velocities


Reformatting PBO GPS Time Series Files' Header for IDV Use

This section is in case you want to make your own data files. The standard data is already converted and available as described above.

The source of time series data for these GPS stations, is PBO GPS Products. Do "save target as" for the "Position Time Series" link. This is a gzip-tar file. Unpack the file to see lots of the .csv files, one for each station. The header lines must be reformatted to work in the IDV.

    To modify a PBO station  time series data file to use in the IDV, the header lines such as
    
    PBO Station Position Time Series
    Format Version,1.0.1
    4-character ID,ELKO
    Station name,ELKO_BRGN_NV1997
    Begin Date,2004-01-07
    End Date,2008-07-28
    Release Date,2008-07-30
    Reference position,40.9146904918 North Latitude,-115.8171979278 East Longitude,2016.89028 meters elevation,
    Date,North (mm),East (mm),Vertical (mm),North Std. Deviation (mm),East Std. Deviation (mm),Vertical Std. Deviation (mm),Quality,
    
    (from ELKO.pbo.csv)
    
    are replaced with 2 lines describing the data character and 4 lines about the station.  Do not alter the caps as in Latitude
    
    (index) -> (Longitude,Latitude,Altitude,Time,Station(Text),North,East,Vertical,Nstddev,Estddev,Vstddev,Quality(Text))
    Longitude[unit="degrees east"],Latitude[unit="deg"],Altitude[unit="meter"],Time[fmt="yyyy-MM-dd"],Station(Text),North[unit="mm"],East[unit="mm"],Vertical[unit="mm"],Nstddev[unit="mm"],Estddev[unit="mm"],Vstddev[unit="mm"],Quality(Text)
    Longitude=-115.8171979278
    Latitude=40.9146904918
    Altitude=2016.89028
    Station=ELKO_BRGN_NV1997
    
    You might name the new file ELKO.pbo.idv.csv.
    
    Here is a sample PBO time series file for the IDV, witrh two stations, ELKO and TRND.


Making Displays - more details

First set the display to a map projection (map area) and a vertical scale suitable for your data. If you are only showing data on the surface, in overhead views, the vertical scale does not matter. Be sure the menu choice Projections -> Auto update projection is checked off.

Connect to a data source with the "UNAVCO IDV Dashboard" window, "Data Chooser" tab. For local files choose the "Files" section, navigate to the file on your local disk, choose the Data Type from the pull down menu, and click "Add source." For data sources with an HTTP server, use section "URLs." If your data is in a .csv file, use Data Type "I'm feeling lucky" which means the IDV recognizes the data type from the file name extension. If your data file is a NetCDF (.nc) file, choose Data Type "NetCDF Point Data files."

After you connect to a data source the Dashboard shows the "Field Selector" for that data. To make a display, in general you choose (click on) a Field name in the "Field Selector" tabbed panel in the Dashboard, then click on a display type in the Displays panel of the same window, and then click on the "Create Display" button.

GPS station data is Field type "Point Data," and the Displays panel shows the choice "Point Data Plot" and "Point Data List." Click on one, then click on the "Create Display" button.

When a display is made the Dashboard shows the "display control" panel for that display. Note the pull down menu called "Layout Model" or "Station Model" which is a list of the plot symbols available for all kinds of data. At first a Point Data Plot display will use plot symbols called "Locations 3D Cross," or whatever happens to be first in the "Layout Model" list. To use another plot symbol, choose one from the list. For GPS velocity vectors, use "GPS Vectors, red" or GPS Vectors, black." (You need the UNAVCO IDV plugin of March 6, 2007 or later to get both colors and vertical components.) Get the latest plugin from the UNAVCO IDV download page.

You can control vector length scaling, using the "Scale" entry box in the Display control window that pops up when the display is made. The Declutter check box reduces the number of symbols in the display. Read more about Point data plots and Working with the Point data Plot Symbols using "Layouts Models"

To zoom, pan, and rotate see Zoom, pan and rotate.

Last modified: Saturday, 12-Dec-2015 04:44:38 UTC