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"""
NOTE: Major TOM standard does not require any specific type of thumbnail to be computed.
Instead these are shared as optional help since this is how the Core dataset thumbnails have been computed.
"""
from rasterio.io import MemoryFile
from PIL import Image
import numpy as np
def s1rtc_thumbnail(vv, vh, vv_NODATA = -32768.0, vh_NODATA = -32768.0):
"""
Takes vv and vh numpy arrays along with the corresponding NODATA values (default is -32768.0)
Returns a numpy array with the thumbnail
"""
# valid data masks
vv_mask = vv != vv_NODATA
vh_mask = vh != vh_NODATA
# remove invalid values before log op
vv[vv<0] = vv[vv>=0].min()
vh[vh<0] = vh[vh>=0].min()
# apply log op
vv_dB = 10*np.log10(vv)
vh_dB = 10*np.log10(vh)
# scale to 0-255
vv_dB = (vv_dB - vv_dB[vv_mask].min()) / (vv_dB[vv_mask].max() - vv_dB[vv_mask].min()) * 255
vh_dB = (vh_dB - vh_dB[vh_mask].min()) / (vh_dB[vh_mask].max() - vh_dB[vh_mask].min()) * 255
# represent nodata as 0
vv_dB[vv_mask==0] = 0
vh_dB[vh_mask==0] = 0
# false colour composite
return np.stack([vv_dB,
255*(vv_dB+vh_dB)/np.max(vv_dB+vh_dB),
vh_dB
],-1).astype(np.uint8)
def s1rtc_thumbnail_from_datarow(datarow):
"""
Takes a datarow directly from one of the data parquet files
Returns a PIL Image
"""
with MemoryFile(datarow['vv'][0].as_py()) as mem_f:
with mem_f.open(driver='GTiff') as f:
vv=f.read().squeeze()
vv_NODATA = f.nodata
with MemoryFile(datarow['vh'][0].as_py()) as mem_f:
with mem_f.open(driver='GTiff') as f:
vh=f.read().squeeze()
vh_NODATA = f.nodata
img = s1rtc_thumbnail(vv, vh, vv_NODATA=vv_NODATA, vh_NODATA=vh_NODATA)
return Image.fromarray(img)
if __name__ == '__main__':
from fsspec.parquet import open_parquet_file
import pyarrow.parquet as pq
print('[example run] reading file from HuggingFace...')
url = "https://huggingface.co/datasets/Major-TOM/Core-S1RTC/resolve/main/images/part_00001.parquet"
with open_parquet_file(url) as f:
with pq.ParquetFile(f) as pf:
first_row_group = pf.read_row_group(1)
print('[example run] computing the thumbnail...')
thumbnail = s1rtc_thumbnail_from_datarow(first_row_group)
thumbnail_fname = 'example_thumbnail.png'
thumbnail.save(thumbnail_fname, format = 'PNG')
print('[example run] saved as "{}"'.format(thumbnail_fname)) |