captainobvious62 / nllgrid

Python class for reading and writing NLLoc grid files.

NLLGrid

Python class for reading and writing NonLinLoc grid files.

(c) 2015-2018 Claudio Satriano, Natalia Poiata

Installation

Clone or download the project from GitHub, uncompress the archive (if needed), and install the codes by running (from within the main directory):

pip install .

(use pip install -e . to install in developer mode).

Getting Started

Reading a NLL grid

A NLL grid is composed of two files (.hdr and .buf).

To read a NLL grid, do:

>>> from nllgrid import NLLGrid
>>> grd = NLLGrid('somegrid.hdr')

or, using the .buf filename:

>>> grd = NLLGrid('somegrid.buf')

or even without any extension:

>>> grd = NLLGrid('somegrid')

A grid description can be obtained by:

>>> print(grd)

The grid data array is accessed by grd.array. The grid can be plotted doing:

>>> grd.plot()

Use Python introspection (e.g. dir(grd)) to see all the available methods and attributes.

Creating a NLL grid

Suppose that you have a 3D data array stored into a NumPy array called mydata.

First, create an empty NLL grid object:

>>> from nllgrid import NLLGrid
>>> grd = NLLGrid()

then, add the data array and information on grid sampling and grid origin, e.g.:

>>> grd.array = mydata
>>> grd.dx = 0.5  #km
>>> grd.dy = 0.5  #km
>>> grd.dz = 0.5  #km
>>> grd.x_orig = -10  #km
>>> grd.y_orig = -20. #km
>>> grd.z_orig = -1.  #km

Optionally, add a grid type and/or a geographic transformation:

>>> grd.type = 'VELOCITY'
>>> grd.orig_lat = 40.63
>>> grd.orig_lon = 15.80
>>> grd.proj_name = 'LAMBERT'
>>> grd.first_std_paral = 38.
>>> grd.second_std_paral = 42.
>>> grd.proj_ellipsoid = 'WGS-84'

Finally, give a basename and write to disk:

>>> grd.basename = 'mygrid'
>>> grd.write_hdr_file()
>>> grd.write_buf_file()

This will create the two files mygrid.hdr and mygrid.buf.

If you want to save your grid in double precision (required for instance by NLDiffLoc), change grd.float_type to 'DOUBLE' before saving the grid (default is 'FLOAT'):

>>> grd.float_type = 'DOUBLE'

Note that if you want to use your grid as input for NonLinLoc Grid2Time code, the grid type has to be SLOW_LEN and your grid array has to be transformed into slowness (in s/km) and multiplied by the grid step (in km).