makegclgrid db [-pf pffile]
This program builds a GCLgrid object and stores the coordinates that define it in a database with a set of external files. A GCLgrid is a general way to build a gridded model in earth coordinates. This program build such an object of a special type. It's primary use is to build a grid of target control points for the cluster program and dbpmel for relocation of an entire catalog. The grid this program produces is about the best attempt one could do for regional scale problems to map a sphere onto a reasonably uniform grid. The process is basically to map the 0,0 point on the earth (i.e. the intersection of the prime meridian and the equator) to a specified origin. The equivalent of the equator is then rotated by a specified angle to provide a baseline. The grid is then defined by equally spaced grid lines defined by this great circle and the pole to it (the x2 axis). See the paramete file description below for more clarification on this.
The program builds this GCLgrid object and stores the result to an output database defined by the db argument. Note this uses an extension table called "gclgrid" that is defined in genloc1.1.
What this program does and how the parameters interact with are best described through and example:
gridname kyrghyz origin_latitude 41.4 origin_longitude 76.0 x_axis_azimuth 80.0 delta_x1 5.0 delta_x2 5.0 delta_x3 2.0 n1 100 n2 100 n3 20 origin_offset_x1 50 origin_offset_x2 50 build_3d_grid true gridfile_directory ./GCLgrids
The origin of the grid makegclgrid would produce with this pf is at 41.4 degrees N and 76.0 degrees east. A baseline great circle path that defines the x1 (x) axis for this example would be projected at an azimuth of 80 degrees (i.e 10 degrees north of east) from this origin. A second great circle path would be draw that defines the x2 (y) axis at -10 degrees azimuth (N 10 degrees W). The x1 and x2 baselines are both divided into 100 points separated by 5 km (this is exact for the baselines). longitude-like lines are drawn perpendicular from the x1 baseline and latitude-like lines are drawn perpendicular to x2. There intersections for the surface, 2D, grid. A 3D grid is constructed of 20 radial surfaces at depth increments of 2.0 km below this surface (i.e. the bottom of the 3D volume for this example will be at a depth of 38 km).
The gridfile_directory and gridname parameters control how the information is stored an indexed. A file containing the computed coordinates with the name defined by gridname (in this case kyrghyz) will be written in the directory defined by gridfiel_directory (for this example the file will be "./GCLgrids/kyrghyz").
The program always produces a 2D grid. It will only compute and save a 3D grid i the build_3d_grid boolean is set true.
cluster(1), dbpmel(1)
Gary L. Pavlis Indiana University pavlis@indiana.edu