Geografic-Information-System/lib/python/vector.py

"""!@package grass.script.vector

@brief GRASS Python scripting module

Vector related functions to be used in Python scripts.

Usage:

@code
from grass.script import core, vector as grass

grass.parser()
grass.vector_db(map)
...
@endcode

(C) 2008-2009 by the GRASS Development Team
This program is free software under the GNU General Public
License (>=v2). Read the file COPYING that comes with GRASS
for details.

@author Glynn Clements
@author Martin Landa <landa.martin gmail.com>
"""

import os

from core import *

# run "v.db.connect -g ..." and parse output

def vector_db(map, **args):
    """!Return the database connection details for a vector map
    (interface to `v.db.connect -g'). Example:
    
    \code
    >>> grass.vector_db('lakes')
    {1: {'layer': '1', 'name': '',
    'database': '/home/martin/grassdata/nc_spm_08/PERMANENT/dbf/',
    'driver': 'dbf', 'key': 'cat', 'table': 'lakes'}}
    \endcode

    @param map vector map
    @param args

    @return dictionary { layer : { 'layer', 'table, 'database', 'driver', 'key' }
    """
    s = read_command('v.db.connect', flags = 'g', map = map, fs = ';', **args)
    result = {}
    
    for l in s.splitlines():
	f = l.split(';')
	if len(f) != 5:
	    continue
        
        if '/' in f[0]:
            f1 = f[0].split('/')
            layer = f1[0]
            name = f1[1]
        else:
            layer = f[0]
            name = ''
            
	result[int(layer)] = {
            'layer'    : layer,
            'name'     : name,
            'table'    : f[1],
            'key'      : f[2],
            'database' : f[3],
            'driver'   : f[4] }
    
    return result

def vector_layer_db(map, layer):
    """!Return the database connection details for a vector map layer.
    If db connection for given layer is not defined, fatal() is called.

    @param map map name
    @param layer layer number

    @return parsed output
    """
    try:
        f = vector_db(map)[int(layer)]
    except KeyError:
	grass.fatal("Database connection not defined for layer %s" % layer)

    return f

# run "v.info -c ..." and parse output

def vector_columns(map, layer = None, **args):
    """!Return a dictionary of the columns for the database table connected to
    a vector map (interface to `v.info -c').

    @param map map name
    @param layer layer number (None for all layers)
    @param args
    
    @return parsed output
    """
    s = read_command('v.info', flags = 'c', map = map, layer = layer, quiet = True, **args)
    result = {}
    for line in s.splitlines():
	f = line.split('|')
	if len(f) == 2:
            result[f[1]] = f[0]
    
    return result

# add vector history

def vector_history(map):
    """!Set the command history for a vector map to the command used to
    invoke the script (interface to `v.support').

    @param map mapname

    @return v.support output
    """
    run_command('v.support', map = map, cmdhist = os.environ['CMDLINE'])

# run "v.info -t" and parse output

def vector_info_topo(map):
    """!Return information about a vector map (interface to `v.info
    -t'). Example:

    \code
    >>> grass.vector_info_topo('lakes')
    {'kernels': 0, 'lines': 0, 'centroids': 15279,
    'boundaries': 27764, 'points': 0, 'faces': 0,
    'primitives': 43043, 'islands': 7470, 'nodes': 35234, 'map3d': 0, 'areas': 15279}
    \endcode
    
    @param map map name

    @return parsed output
    """
    s = read_command('v.info', flags = 't', map = map)
    return parse_key_val(s, val_type = int)

# interface for v.db.select

def vector_db_select(map, layer = 1, **kwargs):
    """!Get attribute data of selected vector map layer.

    Function returns list of columns and dictionary of values ordered by
    key column value. Example:

    \code
    >>> print grass.vector_select('lakes')['values'][3]
    ['3', '19512.86146', '708.44683', '4', '55652', 'LAKE/POND', '39000', '']
    \endcode

    @param map map name
    @param layer layer number
    @param kwargs v.db.select options

    @return dictionary ('columns' and 'values')
    """
    try:
        key = vector_db(map = map)[layer]['key']
    except KeyError:
        error('Missing layer %d in vector map <%s>' % (layer, map))
        return { 'columns' : [], 'values' : {} }
        
    if kwargs.has_key('columns'):
        if key not in kwargs['columns'].split(','):
            # add key column if missing
            debug("Adding key column to the output")
            kwargs['columns'] += ',' + key
    
    ret = read_command('v.db.select',
                       map = map,
                       layer = layer,
                       fs = '|', **kwargs)
    
    if not ret:
        error('vector_select() failed')
        return { 'columns' : [], 'values' : {} }
    
    columns = []
    values = {}
    for line in ret.splitlines():
        if not columns:
            columns = line.split('|')
            key_index = columns.index(key)
            continue
        
        value = line.split('|')
        key_value = int(value[key_index])
        values[key_value] = line.split('|')
    
    return { 'columns' : columns,
             'values' : values }