SeisGram2K LiveSeis - how it works
The LiveSeis near-real time data monitor uses standard http requests to access over the internet recent seismic data segments contained in a circular disk-file buffer.
Circular disk-file buffer - the core of the LiveSeis system. This buffer consists of a fixed number of data segment files and a pointer file "liveseis.last", all of which reside in a public http:// directory that is accessed through a standard web server. The data segment files include an index number in their filenames; they contain data segments written in order of this index number, looping back to 0 after the highest number. The pointer file "liveseis.last" contains the index number of the last written segment file.
Existing aquisition, telemetry and database system - digital seismic ground motion data is recieved from remote stations and stored in a database on disk or in memory buffers.
Segment preparation script - extracts a new data segment from the database at regular intervals, writes the new segment to the circular disk buffer, and updates the "liveseis.last" pointer file with the index number of the file containing the new segment .
LiveSeis operation - Initialisation: The LiveSeis manger object in the SeisGram2K seismogram viewer makes an http request to read the file "liveseis.last" and obtain the index of the last written file. With this information, the manager can construct the filenames for and read all the data segments required for the initial data display . Running: At regular time intervals, the LiveSeis manger makes an http request to check the update time of the file "liveseis.last". When this file has been updated, the LiveSeis manger reads it to obtain the index of the new last-written data segment file. The manager then reads the new data segment and appends it to the displayed data .