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<p class="MsoNormal">Hi Dustin,<o:p></o:p></p>
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<p class="MsoNormal">I can’t speak to nom-tam-fits support for what you want to do, but FITS tile compression is designed for this, eg: “Dividing the image into tiles before compression enables faster access to small sections of the image because only those
tiles covering the area of interest need be uncompressed.” (<a href="https://heasarc.gsfc.nasa.gov/FTP/software/fitsio/c/docs/fpackguide.pdf">https://heasarc.gsfc.nasa.gov/FTP/software/fitsio/c/docs/fpackguide.pdf</a>)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">See the discussion under ZTILEn in the FITS convention (<a href="https://fits.gsfc.nasa.gov/registry/tilecompression/tilecompression2.3.pdf">https://fits.gsfc.nasa.gov/registry/tilecompression/tilecompression2.3.pdf</a>) for the header
keywords to sort it out. Either you or the library will then need to index from the table into the heap. By default, the tiles are row-by-row which makes the arithmetic easier. If there are constraints on the sub-images of interest such as location or size,
the tiles can be tuned to optimize access.<o:p></o:p></p>
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<p class="MsoNormal">Rob<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">On 10/18/22, 7:29 PM, "fitsbits" wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">I’m using the nom-tam-fits Java library to extract a sub image from a compressed image binary table. Typically, the compressed image is decompressed and one can perform a normal extraction, but my service exists
on the Cloud and needs to be able to cutout in a streaming manner. Is there a way to look at the Header and know what row in the table (or which tile) that overlaps some range of pixels? Alternatively, would I need to iterate the tiles to see if any of them
overlap?<br>
<br>
Many thanks,<br>
Dustin<br>
CADC<br>
<br>
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