Input and output of Landlab raster-grid data in ESRI Ascii Raster format

Read/write data from an ESRI ASCII file into a RasterModelGrid.

ESRI ASCII functions

read_asc_header(asc_file)	Read header information from an ESRI ASCII raster file.
read_esri_ascii(asc_file[, grid, reshape, ...])	Read RasterModelGrid from an ESRI ASCII file.
write_esri_ascii(path, fields[, names, clobber])	Write landlab fields to ESRI ASCII.

exception BadHeaderLineError(line)

Bases: landlab.io.esri_ascii.Error

Raise this error for a bad header is line.

exception DataSizeError(size, expected_size)

Bases: landlab.io.esri_ascii.Error

Raise this error if the size of data does not match the header.

exception Error

Bases: exceptions.Exception

Base class for errors in this module.

exception KeyTypeError(key, expected_type)

Bases: landlab.io.esri_ascii.Error

Raise this error when a header’s key value is of the wrong type.

exception KeyValueError(key, message)

Bases: landlab.io.esri_ascii.Error

Raise this error when a header’s key value has a bad value.

exception MismatchGridDataSizeError(size, expected_size)

Bases: landlab.io.esri_ascii.Error

Raise this error if the data size does not match the grid size.

exception MissingRequiredKeyError(key)

Bases: landlab.io.esri_ascii.Error

Raise this error when a header is missing a required key.

read_asc_header(asc_file)

Read header information from an ESRI ASCII raster file.

The header contains the following variables,

• ncols: Number of cell columns
• nrows: Number of cell rows

• xllcenter or xllcorner: X (column) coordinate of lower-left

  coordinate of grid (by center or lower-left corner of the cell)

• yllcenter, yllcorner: Y (row) coordinate of lower-left

  coordinate of grid (by center or lower-left corner of the cell)

• cellsize: Grid spacing between rows and columns
• nodata_value: No-data value (optional)

Parameters:

asc_file : file_like

File-like object from which to read header.

Returns:

dict

Header as key-value pairs.

Raises:

MissingRequiredKeyError

The header is missing a required key.

KeyTypeError

The header has the key but its values is of the wrong type.

Examples

>>> from six import StringIO
>>> from landlab.io.esri_ascii import read_asc_header
>>> contents = StringIO('''
...     nrows 100
...     ncols 200
...     cellsize 1.5
...     xllcenter 0.5
...     yllcenter -0.5
... ''')
>>> hdr = read_asc_header(contents)
>>> hdr['nrows'], hdr['ncols']
(100, 200)
>>> hdr['cellsize']
1.5
>>> hdr['xllcenter'], hdr['yllcenter']
(0.5, -0.5)

MissingRequiredKey is raised if the header does not contain all of the necessary keys.

>>> contents = StringIO('''
...     ncols 200
...     cellsize 1.5
...     xllcenter 0.5
...     yllcenter -0.5
... ''')
>>> read_asc_header(contents) 
Traceback (most recent call last):
MissingRequiredKeyError: nrows

KeyTypeError is raises if a value is of the wrong type. For instance, nrows and ncols must be int.

>>> contents = StringIO('''
...     nrows 100.5
...     ncols 200
...     cellsize 1.5
...     xllcenter 0.5
...     yllcenter -0.5
... ''')
>>> read_asc_header(contents) 
Traceback (most recent call last):
KeyTypeError: Unable to convert nrows to <type 'int'>

read_esri_ascii(asc_file, grid=None, reshape=False, name=None, halo=0)

Read RasterModelGrid from an ESRI ASCII file.

Read data from asc_file, an ESRI ASCII file, into a RasterModelGrid. asc_file is either the name of the data file or is a file-like object.

The grid and data read from the file are returned as a tuple (grid, data) where grid is an instance of RasterModelGrid and data is a numpy array of doubles with that has been reshaped to have the number of rows and columns given in the header.

Parameters:

asc_file : str of file-like

Data file to read.

reshape : boolean, optional

Reshape the returned array, otherwise return a flattened array.

name : str, optional

Add data to the grid as a named field.

grid : grid , optional

Adds data to an existing grid instead of creating a new one.

halo : integer, optional

Adds outer border of depth halo to the grid.

Returns:

(grid, data) : tuple

A newly-created RasterModel grid and the associated node data.

Raises:

DataSizeError

Data are not the same size as indicated by the header file.

MismatchGridDataSizeError

If a grid is passed, the size of the grid does not agree with the size of the data.

Examples

Assume that fop is the name of a file that contains text below (make sure you have your path correct): ncols 3 nrows 4 xllcorner 1. yllcorner 2. cellsize 10. NODATA_value -9999 0. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. ——– >>> from landlab.io import read_esri_ascii >>> (grid, data) = read_esri_ascii(‘fop’) # doctest: +SKIP >>> #grid is an object of type RasterModelGrid with 4 rows and 3 cols >>> #data contains an array of length 4*3 that is equal to >>> # [9., 10., 11., 6., 7., 8., 3., 4., 5., 0., 1., 2.] >>> (grid, data) = read_esri_ascii(‘fop’, halo=1) # doctest: +SKIP >>> #now the data has a nodata_value ring of -9999 around it. So array is >>> # [-9999, -9999, -9999, -9999, -9999, -9999, >>> # -9999, 9., 10., 11., -9999, >>> # -9999, 6., 7., 8., -9999, >>> # -9999, 3., 4., 5., -9999, >>> # -9999, 0., 1., 2. -9999, >>> # -9999, -9999, -9999, -9999, -9999, -9999]

write_esri_ascii(path, fields, names=None, clobber=False)

Write landlab fields to ESRI ASCII.

Write the data and grid information for fields to path in the ESRI ASCII format.

Parameters:

path : str

Path to output file.

fields : field-like

Landlab field object that holds a grid and associated values.

names : iterable of str, optional

Names of the fields to include in the output file. If not provided, write all fields.

clobber : boolean

If path exists, clobber the existing file, otherwise raise an exception.

Examples

>>> import numpy as np
>>> from landlab.testing.tools import cdtemp
>>> from landlab import RasterModelGrid
>>> from landlab.io.esri_ascii import write_esri_ascii

>>> grid = RasterModelGrid((4, 5), spacing=(2., 2.))
>>> _ = grid.add_field('node', 'air__temperature', np.arange(20.))
>>> with cdtemp() as _:
...     files = write_esri_ascii('test.asc', grid)
>>> files
['test.asc']

>>> _ = grid.add_field('node', 'land_surface__elevation', np.arange(20.))
>>> with cdtemp() as _:
...     files = write_esri_ascii('test.asc', grid)
>>> files.sort()
>>> files
['test_air__temperature.asc', 'test_land_surface__elevation.asc']