Re: Speed up reading rasters

Sean Gillies


On Mon, Apr 27, 2020 at 2:36 AM <carlogarro@...> wrote:
Hello, thank you so much for your recommendation, it speed it up x5. Very useful. Now I am having a problem that i do not understand.

I have the following script, where i access 10 random tiles of my raster. train_data is a vector [4822,2] of pixels position in the raster.
for i in range(10):
    idx = np.random.randint(4822)
    x_idx = train_data[idx][1]
    y_idx = train_data[idx][0]
    window = Window(y_idx, x_idx, 224, 224)
    start_time = time.time()
    with'./sentinel2_tiled.tif') as src:
        sentinel2 =
    end_time = (time.time() - start_time)

I do not understand why the times of loading a window are so different, as can be seen in the following image. Do you have some explanation?

 Thank you once more!

I can't say for sure about the time differences because I don't know much about your data files or your computer. However, know this: GDAL's I/O system caches blocks of raster data in memory, the size of the cache is generally 5% of your computers memory, and windowed reads may or may not be served directly from the cache depending on their size and adjacency to previously read data.

Sean Gillies

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