[gdal-dev] python downsample API?

[Anton Korosov]

Hi Michael,

I do that maybe in an awkward way but it saves time.

1. I create a VRT file (e.g. using CreateCopy) and open it using 
xml.etree.ElementTree.XML
2. I decrease rasterXSize and rasterYSize attributes of the VRTDataset tag
3. I also decrease xSize and ySize attributes of the DstRect tag
4. Then I save the VRT and open it again using gdal.Open
5. When I use ReadAsArray it downscales the matrix automatically

Unfortunately I cannot provide the code in a single piece - it is 
dissolved in a large package.

Anton

On 04/11/2012 04:31 PM, K.-Michael Aye wrote:
> Dear all,
>
> is there a Python API for downsampling a huge dataset?
> What I would like to do:
>
> * get my dataset
> * read out RasterXSize and RasterYSize
> * calculate how many lines and rows I need to skip to get a quick
> overview image, e.g. 10 lines to skip.
> * Have a ReadAsArray interface where I can say something like this:
> ** data = ds.ReadAsArray(xoffset, yoffset, 10000, 10000, skipping=10)
>
> which in numpy terms would give me every 10nth line like this:
> array[:,:,10]
>
> I really don't need quality at all, just speed, for a rough overview for
> further zooming in with lassos, as the images I deal with sometimes have
> more than 200 MPixels.
>
> Is this possible in Python?
> I was thinking now, maybe one could use numpy's memmap somehow for this,
> don't know much about it, though…
>
> Thanks for any hints!
>
> Best regards,
> Michael
>
>
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