[gdal-dev] Slow speed in remote reading

[Patrick Young]

You can check how a S2 COG compares at

https://registry.opendata.aws/sentinel-2-l2a-cogs/

You should hopefully see a lot less network requests when accessing a sub
block directly.

P


On Mon, Nov 2, 2020 at 7:58 AM Alexander Verbitsky <habibutsu at gmail.com>
wrote:

> Hi All, I am trying to implement remote reading small blocks of images,
> but find slow performance.
>
> For example i am trying to read 100x100 block from `sentinel-2` image,
> with using following code:
>
> filename = (
>     '/vsigs/gcp-public-data-sentinel-2/tiles/31/U/FS/'
>     'S2A_MSIL1C_20201024T104121_N0209_R008_T31UFS_20201024T125115.SAFE/'
>
> 'GRANULE/L1C_T31UFS_A027890_20201024T104121/IMG_DATA/T31UFS_20201024T104121_B08.jp2'
> )
> ds = gdal.OpenEx(filename, gdal.OF_RASTER)
> band = ds.GetRasterBand(1)
> img = band.ReadAsArray(1000, 1000, 100, 100)
>
> In result I am getting more low performance in comparison if I just
> download the whole image in memory and then read the necessary block. AS I
> understand it happens due to a lot of small requests (is about 100)  that
> are made during reading a small part of the image. Is it a fundamental
> feature of JP2OpenJPEG and this format not suitable for doing things like
> that? Should I take another format like GeoTiff and store my own data in
> it? Thank, for your reply.
>
>
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