Users of a GSAC Repository are able to find metadata information and access data. The user can interact with a GSAC Repository with forms on its web page, or through API calls, or with a client program. Using the UNAVCO GSAC Repository (link available upon request) in combination with the user guide will help you get started. Note that the API details can vary (in a limited way) from one GSAC Repository to another. For each Repository that you use, you may need to check details of the user information in the online 'Information' page of the Repository.
To use GSAC, refer to UNAVCO GSAC User Guide.
GSAC is a set of web services for geodesy data repositoires, for searches about instrumented stations and the instruments, and to download data files from the instruments. GSAC provides
Here are some examples of geodesy station information and data file retrieval from the UNAVCO GSAC repository, with one Linux command directly from the user's command line. This is a simple way to get data, and also quite powerful.
On a Linux or UNIX machine with the "curl" utility, usually at /usr/bin/curl, copy this next line and enter it as a command on a terminal command line:
curl ... /gsacws/gsacapi/site/search/sites?output=site.snx\&site.code=p123\&site.interval=interval.normal
This should list on your terminal a SINEX file created by the main UNAVCO GSAC repository, for the GNSS station whose code (ID) is P123. The 'arguments' in the command follow the "?" and the "\&". The command:
curl ... /gsacws/gsacapi/site/search/sites?output=site.snx\&site.code=P30*\&site.interval=interval.normal
This should list on your terminal a SINEX file for all GNSS stations whose code (ID) begins with "P30" (ten stations in this case). For several distinct stations by each code(ID):
curl ... /gsacws/gsacapi/site/search?site.code=P120&site.code=MTWO&site.code=AB04&output=site.snx\&site.interval=interval.normal
(Note this gets data from two stations with ID P120.) Or both ways, by individual names and with a search for IDs like AB0*:
curl ... /gsacws/gsacapi/site/search?site.code=P120&site.code=MTWO&site.code=AB0*&output=site.snx\&site.interval=interval.normal
GSAC correctly merges the information from all stations found into one SINEX file.
To get data from only continuous stations in the UNAVCO main GSAC (not campaign stations) add the argument
To get results in GAMIT station.info format, use argument output=site.station.info:
curl ... /gsacws/gsacapi/site/search/sites?output=site.station.info\&site.code=p123
To make results in the "SOPAC XML log file" format, use output=site.xmllog; for JSON use output=site.json; for a CSV file use output=site.csv.full.
To get stations inside a latitude-longitude bounding box (region), use these spatial bounding arguments; for example, a box bounded in latitude by 40° N and 30° N and bounded in longitude by -100° and -110°, noting that 100° west longitude = 260° east longitude (i.e. longitude is in positive degrees east):
bbox.north=40.0 for latitudes =40.0 bbox.south=30.0 for latitudes =30.0 bbox.east=-100.0 for longitudes =-100.0 bbox.west=-110.0 for longitudes =-110.0
Also you can limit the station count returned with the argument limit=[some number], such as limit=25. For example:
curl ... /gsacws/gsacapi/site/search/sites?output=site.station.info\&bbox.north=41.0\&bb.east=-104.0\&bb.south=37.0\&bb.west=-112.0\&limit=25
About 5-15 seconds usually completes this request for 25 stations. Add "> demo_station.info" to the end of the command to put the results in a local file named demo_station.info. Lacking the limit=25, this command takes 50 seconds (or more) and returns 575 lines of information in station.info format. The same search, with results in SOPAC XML site log format, takes the same time and returns 31736 lines.
Many parameters (data value types) in a GSAC repository can be used for controlling searches. Each GSAC installation's web site, the Information link, gives all the arguments you can use in API commands like these examples.
Samples of GSAC site query results (station and instrument metadata):
Other formats may be available.
Like other web services, GSAC accepts incoming requests, handles the requests, and returns results. The format of site (station) metadata query results from GSAC is selectable by the user, including HTML (web pages), SINEX, GAMIT station.info files, SOPAC XML site logs, and several more. You can see samples of GSAC site queries' results in differing formats, above.
For data file downloads, GSAC returns a list of URLs with FTP and / or HTTP file addresses, or wget scripts for downloading one or more data files as described above.
Like other web services, you can use the GSAC API and results in JSON, CSV, or XML formats, or the wget commands, to automate search and downloads of geodesy data from a GSAC archive.
GSAC supports federations of two or more individual GSAC Repositories, so that one search or download request can pull from several Repositories at once. Participants in a federated GSAC must conform to some basic GSAC standards to permit simultaneous joint searches for the same parameters.
Last modified: Thursday, 19-Apr-2018 21:52:45 UTC