96 image chips

How to export thousands of image chips from Earth Engine in a few minutes¶

This source code of this notebook was adopted from the Medium post - Fast(er) Downloads by Noel Gorelick. Credits to Noel.

Due to the limitation of the multiprocessing package, the functionality of this notebook can only be run in the top-level. Therefore, it could not be implemented as a function under geemap.

Install packages¶

Uncomment the following line to install the required packages.

In [ ]:

# !pip install geemap retry

# !pip install geemap retry

Import libraries¶

In [ ]:

import ee
import geemap
import logging
import multiprocessing
import os
import requests
import shutil
from retry import retry

import ee import geemap import logging import multiprocessing import os import requests import shutil from retry import retry

Initialize GEE to use the high-volume endpoint¶

• high-volume endpoint

In [ ]:

ee.Initialize(opt_url='https://earthengine-highvolume.googleapis.com')

ee.Initialize(opt_url='https://earthengine-highvolume.googleapis.com')

Create an interactive map¶

In [ ]:

Map = geemap.Map()
Map

Map = geemap.Map() Map

Define the Region of Interest (ROI)¶

You can use the drawing tools on the map to draw an ROI, then you can use Map.user_roi to retrieve the geometry. Alternatively, you can define the ROI as an ee.Geometry as shown below.

In [ ]:

# region = Map.user_roi
region = ee.Geometry.Polygon(
    [
        [
            [-122.513695, 37.707998],
            [-122.513695, 37.804359],
            [-122.371902, 37.804359],
            [-122.371902, 37.707998],
            [-122.513695, 37.707998],
        ]
    ],
    None,
    False,
)

# region = Map.user_roi region = ee.Geometry.Polygon( [ [ [-122.513695, 37.707998], [-122.513695, 37.804359], [-122.371902, 37.804359], [-122.371902, 37.707998], [-122.513695, 37.707998], ] ], None, False, )

Define the image source¶

Using the 1-m NAIP imagery.

In [ ]:

image = (
    ee.ImageCollection('USDA/NAIP/DOQQ')
    .filterBounds(region)
    .filterDate('2020', '2021')
    .mosaic()
    .clip(region)
    .select('N', 'R', 'G')
)

image = ( ee.ImageCollection('USDA/NAIP/DOQQ') .filterBounds(region) .filterDate('2020', '2021') .mosaic() .clip(region) .select('N', 'R', 'G') )

Using the 10-m Sentinel-2 imagery.

In [ ]:

# image = ee.ImageCollection('COPERNICUS/S2_SR') \
#             .filterBounds(region) \
#             .filterDate('2021', '2022') \
#             .select('B8', 'B4', 'B3') \
#             .median() \
#             .visualize(min=0, max=4000) \
#             .clip(region)

# image = ee.ImageCollection('COPERNICUS/S2_SR') \ # .filterBounds(region) \ # .filterDate('2021', '2022') \ # .select('B8', 'B4', 'B3') \ # .median() \ # .visualize(min=0, max=4000) \ # .clip(region)

Set parameters¶

If you want the exported images to have coordinate system, change format to GEO_TIFF. Otherwise, you can use png or jpg formats.

In [ ]:

params = {
    'count': 100,  # How many image chips to export
    'buffer': 127,  # The buffer distance (m) around each point
    'scale': 100,  # The scale to do stratified sampling
    'seed': 1,  # A randomization seed to use for subsampling.
    'dimensions': '256x256',  # The dimension of each image chip
    'format': "png",  # The output image format, can be png, jpg, ZIPPED_GEO_TIFF, GEO_TIFF, NPY
    'prefix': 'tile_',  # The filename prefix
    'processes': 25,  # How many processes to used for parallel processing
    'out_dir': '.',  # The output directory. Default to the current working directly
}

params = { 'count': 100, # How many image chips to export 'buffer': 127, # The buffer distance (m) around each point 'scale': 100, # The scale to do stratified sampling 'seed': 1, # A randomization seed to use for subsampling. 'dimensions': '256x256', # The dimension of each image chip 'format': "png", # The output image format, can be png, jpg, ZIPPED_GEO_TIFF, GEO_TIFF, NPY 'prefix': 'tile_', # The filename prefix 'processes': 25, # How many processes to used for parallel processing 'out_dir': '.', # The output directory. Default to the current working directly }

Add layers to map¶

In [ ]:

Map.addLayer(image, {}, "Image")
Map.addLayer(region, {}, "ROI", False)
Map.setCenter(-122.4415, 37.7555, 12)
Map

Map.addLayer(image, {}, "Image") Map.addLayer(region, {}, "ROI", False) Map.setCenter(-122.4415, 37.7555, 12) Map

Generate a list of work items¶

In the example, we are going to generate 1000 points using the stratified random sampling, which requires a classBand. It is the name of the band containing the classes to use for stratification. If unspecified, the first band of the input image is used. Therefore, we have toADD a new band with a constant value (e.g., 1) to the image. The result of the getRequests()function returns a list of dictionaries containing points.

In [ ]:

def getRequests():
    img = ee.Image(1).rename("Class").addBands(image)
    points = img.stratifiedSample(
        numPoints=params['count'],
        region=region,
        scale=params['scale'],
        seed=params['seed'],
        geometries=True,
    )
    Map.data = points
    return points.aggregate_array('.geo').getInfo()

def getRequests(): img = ee.Image(1).rename("Class").addBands(image) points = img.stratifiedSample( numPoints=params['count'], region=region, scale=params['scale'], seed=params['seed'], geometries=True, ) Map.data = points return points.aggregate_array('.geo').getInfo()

Create a function for downloading image¶

The getResult() function then takes one of those points and generates an image centered on that location, which is then downloaded as a PNG and saved to a file. This function uses image.getThumbURL() to select the pixels, however you could also use image.getDownloadURL() if you wanted the output to be in GeoTIFF or NumPy format (source).

In [ ]:

@retry(tries=10, delay=1, backoff=2)
def getResult(index, point):
    point = ee.Geometry.Point(point['coordinates'])
    region = point.buffer(params['buffer']).bounds()

    if params['format'] in ['png', 'jpg']:
        url = image.getThumbURL(
            {
                'region': region,
                'dimensions': params['dimensions'],
                'format': params['format'],
            }
        )
    else:
        url = image.getDownloadURL(
            {
                'region': region,
                'dimensions': params['dimensions'],
                'format': params['format'],
            }
        )

    if params['format'] == "GEO_TIFF":
        ext = 'tif'
    else:
        ext = params['format']

    r = requests.get(url, stream=True)
    if r.status_code != 200:
        r.raise_for_status()

    out_dir = os.path.abspath(params['out_dir'])
    basename = str(index).zfill(len(str(params['count'])))
    filename = f"{out_dir}/{params['prefix']}{basename}.{ext}"
    with open(filename, 'wb') as out_file:
        shutil.copyfileobj(r.raw, out_file)
    print("Done: ", basename)

@retry(tries=10, delay=1, backoff=2) def getResult(index, point): point = ee.Geometry.Point(point['coordinates']) region = point.buffer(params['buffer']).bounds() if params['format'] in ['png', 'jpg']: url = image.getThumbURL( { 'region': region, 'dimensions': params['dimensions'], 'format': params['format'], } ) else: url = image.getDownloadURL( { 'region': region, 'dimensions': params['dimensions'], 'format': params['format'], } ) if params['format'] == "GEO_TIFF": ext = 'tif' else: ext = params['format'] r = requests.get(url, stream=True) if r.status_code != 200: r.raise_for_status() out_dir = os.path.abspath(params['out_dir']) basename = str(index).zfill(len(str(params['count']))) filename = f"{out_dir}/{params['prefix']}{basename}.{ext}" with open(filename, 'wb') as out_file: shutil.copyfileobj(r.raw, out_file) print("Done: ", basename)

Download images¶

In [ ]:

%%time
logging.basicConfig()
items = getRequests()

pool = multiprocessing.Pool(params['processes'])
pool.starmap(getResult, enumerate(items))

pool.close()

%%time logging.basicConfig() items = getRequests() pool = multiprocessing.Pool(params['processes']) pool.starmap(getResult, enumerate(items)) pool.close()

Retrieve sample points¶

In [ ]:

Map.addLayer(Map.data, {}, "Sample points")
Map

Map.addLayer(Map.data, {}, "Sample points") Map

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Last update: 2023-03-19
Created: 2022-02-05