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gdal_interfaces.py
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import os
from osgeo import gdal, osr
from lazy import lazy
from os import listdir
from os.path import isfile, join, getsize
import json
from rtree import index
# Originally based on https://stackoverflow.com/questions/13439357/extract-point-from-raster-in-gdal
class GDALInterface(object):
SEA_LEVEL = 0
def __init__(self, tif_path):
super(GDALInterface, self).__init__()
self.tif_path = tif_path
self.loadMetadata()
def get_corner_coords(self):
ulx, xres, xskew, uly, yskew, yres = self.geo_transform
lrx = ulx + (self.src.RasterXSize * xres)
lry = uly + (self.src.RasterYSize * yres)
return {
'TOP_LEFT': (ulx, uly),
'TOP_RIGHT': (lrx, uly),
'BOTTOM_LEFT': (ulx, lry),
'BOTTOM_RIGHT': (lrx, lry),
}
def loadMetadata(self):
# open the raster and its spatial reference
self.src = gdal.Open(self.tif_path)
if self.src is None:
raise Exception('Could not load GDAL file "%s"' % self.tif_path)
spatial_reference_raster = osr.SpatialReference(self.src.GetProjection())
# get the WGS84 spatial reference
spatial_reference = osr.SpatialReference()
spatial_reference.ImportFromEPSG(4326) # WGS84
# coordinate transformation
self.coordinate_transform = osr.CoordinateTransformation(spatial_reference, spatial_reference_raster)
gt = self.geo_transform = self.src.GetGeoTransform()
dev = (gt[1] * gt[5] - gt[2] * gt[4])
self.geo_transform_inv = (gt[0], gt[5] / dev, -gt[2] / dev,
gt[3], -gt[4] / dev, gt[1] / dev)
@lazy
def points_array(self):
b = self.src.GetRasterBand(1)
return b.ReadAsArray()
def print_statistics(self):
print(self.src.GetRasterBand(1).GetStatistics(True, True))
def lookup(self, lat, lon):
try:
# get coordinate of the raster
xgeo, ygeo, zgeo = self.coordinate_transform.TransformPoint(lon, lat, 0)
# convert it to pixel/line on band
u = xgeo - self.geo_transform_inv[0]
v = ygeo - self.geo_transform_inv[3]
# FIXME this int() is probably bad idea, there should be half cell size thing needed
xpix = int(self.geo_transform_inv[1] * u + self.geo_transform_inv[2] * v)
ylin = int(self.geo_transform_inv[4] * u + self.geo_transform_inv[5] * v)
# look the value up
v = self.points_array[ylin, xpix]
return v if v != -32768 else self.SEA_LEVEL
except Exception as e:
print(e)
return self.SEA_LEVEL
def close(self):
self.src = None
def __enter__(self):
return self
def __exit__(self, type, value, traceback):
self.close()
class GDALTileInterface(object):
def __init__(self, tiles_folder, summary_file, open_interfaces_size=5):
super(GDALTileInterface, self).__init__()
self.tiles_folder = tiles_folder
self.summary_file = summary_file
self.index = index.Index()
self.cached_open_interfaces = []
self.cached_open_interfaces_dict = {}
self.open_interfaces_size = open_interfaces_size
def _open_gdal_interface(self, path):
if path in self.cached_open_interfaces_dict:
interface = self.cached_open_interfaces_dict[path]
self.cached_open_interfaces.remove(path)
self.cached_open_interfaces += [path]
return interface
else:
interface = GDALInterface(path)
self.cached_open_interfaces += [path]
self.cached_open_interfaces_dict[path] = interface
if len(self.cached_open_interfaces) > self.open_interfaces_size:
last_interface_path = self.cached_open_interfaces.pop(0)
last_interface = self.cached_open_interfaces_dict[last_interface_path]
last_interface.close()
self.cached_open_interfaces_dict[last_interface_path] = None
del self.cached_open_interfaces_dict[last_interface_path]
return interface
def _all_files(self):
return [f for f in listdir(self.tiles_folder) if isfile(join(self.tiles_folder, f)) and f.endswith(u'.tif')]
def has_summary_json(self):
return os.path.exists(self.summary_file)
def create_summary_json(self):
all_coords = []
for file in self._all_files():
full_path = join(self.tiles_folder,file)
print('Processing %s ... (%s MB)' % (full_path, getsize(full_path) / 2**20))
i = self._open_gdal_interface(full_path)
coords = i.get_corner_coords()
lmin, lmax = coords['BOTTOM_RIGHT'][1], coords['TOP_RIGHT'][1]
lngmin, lngmax = coords['TOP_LEFT'][0], coords['TOP_RIGHT'][0]
all_coords += [
{
'file': full_path,
'coords': ( lmin, # latitude min
lmax, # latitude max
lngmin, # longitude min
lngmax, # longitude max
)
}
]
print('\tDone! LAT (%s,%s) | LNG (%s,%s)' % (lmin, lmax, lngmin, lngmax))
with open(self.summary_file, 'w') as f:
json.dump(all_coords, f)
self.all_coords = all_coords
self._build_index()
def read_summary_json(self):
with open(self.summary_file) as f:
self.all_coords = json.load(f)
self._build_index()
def lookup(self, lat, lng):
nearest = list(self.index.nearest((lat, lng), 1, objects=True))
if not nearest:
raise Exception('Invalid latitude/longitude')
else:
coords = nearest[0].object
gdal_interface = self._open_gdal_interface(coords['file'])
return int(gdal_interface.lookup(lat, lng))
def _build_index(self):
print('Building spatial index ...')
index_id = 1
for e in self.all_coords:
e['index_id'] = index_id
left, bottom, right, top = (e['coords'][0], e['coords'][2], e['coords'][1], e['coords'][3])
self.index.insert( index_id, (left, bottom, right, top), obj=e)