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Python

# -*- coding: utf-8 -*-
"""
Created on Thu Mar 1 11:20:35 2018
@author: z5030440
"""
"""This script contains the functions needed for satellite derived shoreline (SDS) extraction"""
# Initial settings
import numpy as np
import matplotlib.pyplot as plt
import pdb
import ee
# other modules
from osgeo import gdal, ogr, osr
import tempfile
from urllib.request import urlretrieve
import zipfile
# image processing modules
import skimage.filters as filters
import skimage.exposure as exposure
import skimage.transform as transform
import sklearn.decomposition as decomposition
import skimage.measure as measure
# import own modules
from functions.utils import *
# Download from ee server function
def download_tif(image, polygon, bandsId):
"""downloads tif image (region and bands) from the ee server and stores it in a temp file"""
url = ee.data.makeDownloadUrl(ee.data.getDownloadId({
'image': image.serialize(),
'region': polygon,
'bands': bandsId,
'filePerBand': 'false',
'name': 'data',
}))
local_zip, headers = urlretrieve(url)
with zipfile.ZipFile(local_zip) as local_zipfile:
return local_zipfile.extract('data.tif', tempfile.mkdtemp())
def load_image(image, polygon, bandsId):
"""
Loads an ee.Image() as a np.array. e.Image() is retrieved from the EE database.
The geographic area and bands to select can be specified
KV WRL 2018
Arguments:
-----------
image: ee.Image()
image objec from the EE database
polygon: list
coordinates of the points creating a polygon. Each point is a list with 2 values
bandsId: list
bands to select, each band is a dictionnary in the list containing the following keys:
crs, crs_transform, data_type and id. NOTE: you have to remove the key dimensions, otherwise
the entire image is retrieved.
Returns:
-----------
image_array : np.ndarray
An array containing the image (2D if one band, otherwise 3D)
georef : np.ndarray
6 element vector containing the crs_parameters
[X_ul_corner Xscale Xshear Y_ul_corner Yshear Yscale]
"""
local_tif_filename = download_tif(image, polygon, bandsId)
dataset = gdal.Open(local_tif_filename, gdal.GA_ReadOnly)
georef = np.array(dataset.GetGeoTransform())
bands = [dataset.GetRasterBand(i + 1).ReadAsArray() for i in range(dataset.RasterCount)]
return np.stack(bands, 2), georef
def create_cloud_mask(im_qa):
"""
Creates a cloud mask from the image containing the QA band information
KV WRL 2018
Arguments:
-----------
im_qa: np.ndarray
Image containing the QA band
Returns:
-----------
cloud_mask : np.ndarray of booleans
A boolean array with True where the cloud are present
"""
# convert QA bits
cloud_values = [2800, 2804, 2808, 2812, 6896, 6900, 6904, 6908]
cloud_mask = np.isin(im_qa, cloud_values)
#cloud_shadow_values = [2976, 2980, 2984, 2988, 3008, 3012, 3016, 3020]
#cloud_shadow_mask = np.isin(im_qa, cloud_shadow_values)
return cloud_mask
def read_eeimage(im, polygon, plot_bool):
"""
Read an ee.Image() object and returns the panchromatic band, multispectral bands (B, G, R, NIR, SWIR)
and a cloud mask. All outputs are at 15m resolution (bilinear interpolation for the multispectral bands)
KV WRL 2018
Arguments:
-----------
im: ee.Image()
Image to read from the Google Earth Engine database
plot_bool: boolean
True if plot is wanted
Returns:
-----------
im_pan: np.ndarray (2D)
The panchromatic band (15m)
im_ms: np.ndarray (3D)
The multispectral bands interpolated at 15m
im_cloud: np.ndarray (2D)
The cloud mask at 15m
crs_params: list
EPSG code and affine transformation parameters
"""
im_dic = im.getInfo()
# save metadata
im_meta = im_dic.get('properties')
meta = {'timestamp':im_meta['system:time_start'],
'date_acquired':im_meta['DATE_ACQUIRED'],
'geom_rmse_model':im_meta['GEOMETRIC_RMSE_MODEL'],
'gcp_model':im_meta['GROUND_CONTROL_POINTS_MODEL'],
'quality':im_meta['IMAGE_QUALITY_OLI'],
'sun_azimuth':im_meta['SUN_AZIMUTH'],
'sun_elevation':im_meta['SUN_ELEVATION']}
im_bands = im_dic.get('bands')
# delete dimensions key from dictionnary, otherwise the entire image is extracted
for i in range(len(im_bands)): del im_bands[i]['dimensions']
# load panchromatic band
pan_band = [im_bands[7]]
im_pan, crs_pan = load_image(im, polygon, pan_band)
im_pan = im_pan[:,:,0]
# load the multispectral bands (B2,B3,B4,B5,B6) = (blue,green,red,nir,swir1)
ms_bands = [im_bands[1], im_bands[2], im_bands[3], im_bands[4], im_bands[5]]
im_ms_30m, crs_ms = load_image(im, polygon, ms_bands)
# create cloud mask
qa_band = [im_bands[11]]
im_qa, crs_qa = load_image(im, polygon, qa_band)
im_qa = im_qa[:,:,0]
im_cloud = create_cloud_mask(im_qa)
im_cloud = transform.resize(im_cloud, (im_pan.shape[0], im_pan.shape[1]),
order=0, preserve_range=True, mode='constant').astype('bool_')
# resize the image using bilinear interpolation (order 1)
im_ms = transform.resize(im_ms_30m,(im_pan.shape[0], im_pan.shape[1]),
order=1, preserve_range=True, mode='constant')
# check if -inf values (means out of image) and add to cloud mask
im_inf = np.isin(im_ms[:,:,0], -np.inf)
im_nan = np.isnan(im_ms[:,:,0])
im_cloud = np.logical_or(np.logical_or(im_cloud, im_inf), im_nan)
# get the crs parameters for the image at 15m and 30m resolution
crs = {'crs_15m':crs_pan, 'crs_30m':crs_ms, 'epsg_code':int(pan_band[0]['crs'][5:])}
if plot_bool:
# if there are -inf in the image, set them to 0 before plotting
if sum(sum(np.isin(im_ms_30m[:,:,0], -np.inf).astype(int))) > 0:
idx = np.isin(im_ms_30m[:,:,0], -np.inf)
im_ms_30m[idx,0] = 0; im_ms_30m[idx,1] = 0; im_ms_30m[idx,2] = 0;
im_ms_30m[idx,3] = 0; im_ms_30m[idx,4] = 0
plt.figure()
plt.subplot(221)
plt.imshow(im_pan, cmap='gray')
plt.title('PANCHROMATIC')
plt.subplot(222)
plt.imshow(im_ms_30m[:,:,[2,1,0]])
plt.title('RGB')
plt.subplot(223)
plt.imshow(im_ms_30m[:,:,3], cmap='gray')
plt.title('NIR')
plt.subplot(224)
plt.imshow(im_ms_30m[:,:,4], cmap='gray')
plt.title('SWIR')
plt.show()
return im_pan, im_ms, im_cloud, crs, meta
def rescale_image_intensity(im, cloud_mask, prob_high, plot_bool):
"""
Rescales the intensity of an image (multispectral or single band) by applying
a cloud mask and clipping the prob_high upper percentile. This functions allows
to stretch the contrast of an image.
KV WRL 2018
Arguments:
-----------
im: np.ndarray
Image to rescale, can be 3D (multispectral) or 2D (single band)
cloud_mask: np.ndarray
2D cloud mask with True where cloud pixels are
prob_high: float
probability of exceedence used to calculate the upper percentile
plot_bool: boolean
True if plot is wanted
Returns:
-----------
im_adj: np.ndarray
The rescaled image
"""
prc_low = 0 # lower percentile
vec_mask = cloud_mask.reshape(im.shape[0] * im.shape[1])
if plot_bool:
plt.figure()
if len(im.shape) > 2:
vec = im.reshape(im.shape[0] * im.shape[1], im.shape[2])
vec_adj = np.ones((len(vec_mask), im.shape[2])) * np.nan
for i in range(im.shape[2]):
prc_high = np.percentile(vec[~vec_mask, i], prob_high)
vec_rescaled = exposure.rescale_intensity(vec[~vec_mask, i], in_range=(prc_low, prc_high))
vec_adj[~vec_mask,i] = vec_rescaled
if plot_bool:
plt.subplot(np.floor(im.shape[2]/2) + 1, np.floor(im.shape[2]/2), i+1)
plt.hist(vec[~vec_mask, i], bins=200, label='original')
plt.hist(vec_rescaled, bins=200, alpha=0.5, label='rescaled')
plt.legend()
plt.title('Band' + str(i+1))
plt.show()
im_adj = vec_adj.reshape(im.shape[0], im.shape[1], im.shape[2])
if plot_bool:
plt.figure()
ax1 = plt.subplot(121)
plt.imshow(im[:,:,[2,1,0]])
plt.axis('off')
plt.title('Original')
ax2 = plt.subplot(122, sharex=ax1, sharey=ax1)
plt.imshow(im_adj[:,:,[2,1,0]])
plt.axis('off')
plt.title('Rescaled')
plt.show()
else:
vec = im.reshape(im.shape[0] * im.shape[1])
vec_adj = np.ones(len(vec_mask)) * np.nan
prc_high = np.percentile(vec[~vec_mask], prob_high)
vec_rescaled = exposure.rescale_intensity(vec[~vec_mask], in_range=(prc_low, prc_high))
vec_adj[~vec_mask] = vec_rescaled
if plot_bool:
plt.hist(vec[~vec_mask], bins=200, label='original')
plt.hist(vec_rescaled, bins=200, alpha=0.5, label='rescaled')
plt.legend()
plt.title('Single band')
plt.show()
im_adj = vec_adj.reshape(im.shape[0], im.shape[1])
if plot_bool:
plt.figure()
ax1 = plt.subplot(121)
plt.imshow(im, cmap='gray')
plt.axis('off')
plt.title('Original')
ax2 = plt.subplot(122, sharex=ax1, sharey=ax1)
plt.imshow(im_adj, cmap='gray')
plt.axis('off')
plt.title('Rescaled')
plt.show()
return im_adj
def hist_match(source, template):
"""
Adjust the pixel values of a grayscale image such that its histogram
matches that of a target image
Arguments:
-----------
source: np.ndarray
Image to transform; the histogram is computed over the flattened
array
template: np.ndarray
Template image; can have different dimensions to source
Returns:
-----------
matched: np.ndarray
The transformed output image
"""
oldshape = source.shape
source = source.ravel()
template = template.ravel()
# get the set of unique pixel values and their corresponding indices and
# counts
s_values, bin_idx, s_counts = np.unique(source, return_inverse=True,
return_counts=True)
t_values, t_counts = np.unique(template, return_counts=True)
# take the cumsum of the counts and normalize by the number of pixels to
# get the empirical cumulative distribution functions for the source and
# template images (maps pixel value --> quantile)
s_quantiles = np.cumsum(s_counts).astype(np.float64)
s_quantiles /= s_quantiles[-1]
t_quantiles = np.cumsum(t_counts).astype(np.float64)
t_quantiles /= t_quantiles[-1]
# interpolate linearly to find the pixel values in the template image
# that correspond most closely to the quantiles in the source image
interp_t_values = np.interp(s_quantiles, t_quantiles, t_values)
return interp_t_values[bin_idx].reshape(oldshape)
def pansharpen(im_ms, im_pan, cloud_mask, plot_bool):
"""
Pansharpens a multispectral image (3D), using the panchromatic band (2D)
and a cloud mask
KV WRL 2018
Arguments:
-----------
im_ms: np.ndarray
Multispectral image to pansharpen (3D)
im_pan: np.ndarray
Panchromatic band (2D)
cloud_mask: np.ndarray
2D cloud mask with True where cloud pixels are
plot_bool: boolean
True if plot is wanted
Returns:
-----------
im_ms_ps: np.ndarray
Pansharpened multisoectral image (3D)
"""
# reshape image into vector and apply cloud mask
vec = im_ms.reshape(im_ms.shape[0] * im_ms.shape[1], im_ms.shape[2])
vec_mask = cloud_mask.reshape(im_ms.shape[0] * im_ms.shape[1])
vec = vec[~vec_mask, :]
# apply PCA to RGB bands
pca = decomposition.PCA()
vec_pcs = pca.fit_transform(vec)
# replace 1st PC with pan band (after matching histograms)
vec_pan = im_pan.reshape(im_pan.shape[0] * im_pan.shape[1])
vec_pan = vec_pan[~vec_mask]
vec_pcs[:,0] = hist_match(vec_pan, vec_pcs[:,0])
vec_ms_ps = pca.inverse_transform(vec_pcs)
# normalise between 0 and 1
for i in range(vec_pcs.shape[1]):
vec_ms_ps[:,i] = np.divide(vec_ms_ps[:,i] - np.min(vec_ms_ps[:,i]),
np.max(vec_ms_ps[:,i]) - np.min(vec_ms_ps[:,i]))
# reshape vector into image
vec_ms_ps_full = np.ones((len(vec_mask), im_ms.shape[2])) * np.nan
vec_ms_ps_full[~vec_mask,:] = vec_ms_ps
im_ms_ps = vec_ms_ps_full.reshape(im_ms.shape[0], im_ms.shape[1], im_ms.shape[2])
if plot_bool:
plt.figure()
ax1 = plt.subplot(121)
plt.imshow(im_ms[:,:,[2,1,0]])
plt.axis('off')
plt.title('Original')
ax2 = plt.subplot(122, sharex=ax1, sharey=ax1)
plt.imshow(im_ms_ps[:,:,[2,1,0]])
plt.axis('off')
plt.title('Pansharpened')
plt.show()
return im_ms_ps
def nd_index(im1, im2, cloud_mask, plot_bool):
"""
Computes normalised difference index on 2 images (2D), given a cloud mask (2D)
KV WRL 2018
Arguments:
-----------
im1, im2: np.ndarray
Images (2D) with which to calculate the ND index
cloud_mask: np.ndarray
2D cloud mask with True where cloud pixels are
plot_bool: boolean
True if plot is wanted
Returns: -----------
im_nd: np.ndarray
Image (2D) containing the ND index
"""
vec_mask = cloud_mask.reshape(im1.shape[0] * im1.shape[1])
vec_nd = np.ones(len(vec_mask)) * np.nan
vec1 = im1.reshape(im1.shape[0] * im1.shape[1])
vec2 = im2.reshape(im2.shape[0] * im2.shape[1])
temp = np.divide(vec1[~vec_mask] - vec2[~vec_mask],
vec1[~vec_mask] + vec2[~vec_mask])
vec_nd[~vec_mask] = temp
im_nd = vec_nd.reshape(im1.shape[0], im1.shape[1])
if plot_bool:
plt.figure()
plt.imshow(im_nd, cmap='seismic')
plt.colorbar()
plt.title('Normalised index')
plt.show()
return im_nd
def find_wl_contours(im_ndwi, cloud_mask, min_contour_points, plot_bool):
"""
Computes normalised difference index on 2 images (2D), given a cloud mask (2D)
KV WRL 2018
Arguments:
-----------
im_ndwi: np.ndarray
Image (2D) with the NDWI (water index)
cloud_mask: np.ndarray
2D cloud mask with True where cloud pixels are
min_contour_points: int
minimum number of points in each contour line
plot_bool: boolean
True if plot is wanted
Returns: -----------
contours_wl: list of np.arrays
contains the (row,column) coordinates of the contour lines
"""
# reshape image to vector
vec_ndwi = im_ndwi.reshape(im_ndwi.shape[0] * im_ndwi.shape[1])
vec_mask = cloud_mask.reshape(cloud_mask.shape[0] * cloud_mask.shape[1])
vec = vec_ndwi[~vec_mask]
# apply otsu's threshold
t_otsu = filters.threshold_otsu(vec)
# use Marching Squares algorithm to detect contours on ndwi image
contours = measure.find_contours(im_ndwi, t_otsu)
# filter water lines
contours_wl = []
for i, contour in enumerate(contours):
# remove contour points that are around clouds (nan values)
if np.any(np.isnan(contour)):
index_nan = np.where(np.isnan(contour))[0]
contour = np.delete(contour, index_nan, axis=0)
# remove contours that have only few points (less than min_contour_points)
if contour.shape[0] > min_contour_points:
contours_wl.append(contour)
if plot_bool:
# plot otsu's histogram segmentation
plt.figure()
vals = plt.hist(vec, bins=200)
plt.plot([t_otsu, t_otsu],[0, np.max(vals[0])], 'r-', label='Otsu threshold')
plt.legend()
plt.show()
# plot the water line contours on top of water index
plt.figure()
plt.imshow(im_ndwi, cmap='seismic')
plt.colorbar()
for i,contour in enumerate(contours_wl): plt.plot(contour[:, 1], contour[:, 0], linewidth=3, color='k')
plt.axis('image')
plt.title('Detected water lines')
plt.show()
return contours_wl
def convert_pix2world(points, crs_vec):
"""
Converts pixel coordinates (row,columns) to world projected coordinates
performing an affine transformation
KV WRL 2018
Arguments:
-----------
points: np.ndarray or list of np.ndarray
array with 2 columns (rows first and columns second)
crs_vec: np.ndarray
vector of 6 elements [Xtr, Xscale, Xshear, Ytr, Yshear, Yscale]
Returns: -----------
points_converted: np.ndarray or list of np.ndarray
converted coordinates, first columns with X and second column with Y
"""
# make affine transformation matrix
aff_mat = np.array([[crs_vec[1], crs_vec[2], crs_vec[0]],
[crs_vec[4], crs_vec[5], crs_vec[3]],
[0, 0, 1]])
# create affine transformation
tform = transform.AffineTransform(aff_mat)
if type(points) is list:
points_converted = []
# iterate over the list
for i, arr in enumerate(points):
tmp = arr[:,[1,0]]
points_converted.append(tform(tmp))
elif type(points) is np.ndarray:
tmp = points[:,[1,0]]
points_converted = tform(tmp)
else:
print('invalid input type')
raise
return points_converted
def convert_epsg(points, epsg_in, epsg_out):
"""
Converts from one spatial reference to another using the epsg codes
KV WRL 2018
Arguments:
-----------
points: np.ndarray or list of np.ndarray
array with 2 columns (rows first and columns second)
epsg_in: int
epsg code of the spatial reference in which the input is
epsg_out: int
epsg code of the spatial reference in which the output will be
Returns: -----------
points_converted: np.ndarray or list of np.ndarray
converted coordinates
"""
# define input and output spatial references
inSpatialRef = osr.SpatialReference()
inSpatialRef.ImportFromEPSG(epsg_in)
outSpatialRef = osr.SpatialReference()
outSpatialRef.ImportFromEPSG(epsg_out)
# create a coordinates transform
coordTransform = osr.CoordinateTransformation(inSpatialRef, outSpatialRef)
# transform points
if type(points) is list:
points_converted = []
# iterate over the list
for i, arr in enumerate(points):
points_converted.append(np.array(coordTransform.TransformPoints(arr)))
elif type(points) is np.ndarray:
points_converted = np.array(coordTransform.TransformPoints(points))
else:
print('invalid input type')
raise
return points_converted