NLLGrid

Python class for reading and writing NonLinLoc grid files.

(c) 2015-2017 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.

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).