Source code for karta.raster._aai

""" Low-level functions for reading ESRI ASCII grids """

import numpy as np

[docs]def aairead(fnm): """ Read an existing ASCII grid file and return a Numpy array and a dictionary of header information. """ h = [] with open(fnm, 'r') as f: # Count the number of header entries cnt = 0 while True: l = f.readline() if l.split(None, 1)[0].lower() in ['nrows', 'ncols', 'yllcenter', 'xllcenter', 'yllcorner', 'xllcorner', 'cellsize', 'nodata_value']: cnt += 1 else: break # Read the header, then the array data for _ in range(cnt): h.append(f.readline()) data = f.readlines() # Store data internally hs = [rec.split(None, 1) for rec in h] hdr = dict([(rec[0].lower(), float(rec[1])) for rec in hs]) hdr['ncols'] = int(hdr['ncols']) hdr['nrows'] = int(hdr['nrows']) if 'yllcenter' not in hdr.keys(): hdr['yllcenter'] = None if 'xllcenter' not in hdr.keys(): hdr['xllcenter'] = None if 'yllcorner' not in hdr.keys(): hdr['yllcorner'] = None if 'xllcorner' not in hdr.keys(): hdr['xllcorner'] = None if 'nodata_value' not in hdr.keys(): hdr['nodata_value'] = -9999 check_header(hdr) f = lambda l: [float(i) for i in l.split()] data_f = list(map(f, data)) data_a = np.array(data_f) data_a[data_a==hdr['nodata_value']] = np.nan return data_a, hdr
[docs]def check_header(hdr): """ Make sure that all required header records are present, as well as both centered and corner spatial references. """ for field in ('ncols', 'nrows', 'cellsize'): if field not in hdr: raise ValueError("{0} not set in header".format(field.upper())) d = hdr['cellsize'] if hdr.get('yllcenter') is None: if hdr.get('yllcorner') is None: raise ValueError('YLL reference not set in header') else: hdr['yllcenter'] = hdr['yllcorner'] + d / 2.0 else: hdr['yllcorner'] = hdr['yllcenter'] - d / 2.0 if hdr.get('xllcenter') is None: if hdr.get('xllcorner') is None: raise ValueError('XLL reference not set in header') else: hdr['xllcenter'] = hdr['xllcorner'] + d / 2.0 else: hdr['xllcorner'] = hdr['xllcenter'] - d / 2.0 return hdr