[mapserver-users] preparing orthos for Mapserver?

[Rahkonen Jukka]

Andrea Aime wrote:

> Hi Frank,
> this is quite interesting. Can you elaborate a bit of what "one block scanline" means?
> E.g., what is the actual tiling structure of this file?
> Does presence of compression affect the ability to do the subsampling?
> How about quality of the output? (e.g., is GDAL reading one pixel every N to generate
> the reduced resolution version?)

One scanline blocks can be created by using GeoTIFF creation option BLOCKYSIZE.
For example

gdal_translate -of GTiff -co blockysize=1 -outsize 1000 1000 test_in.TIF test_out.tif

gdalinfo test_out.tif
...
...
Band 1 Block=1000x1 Type=Byte, ColorInterp=Red
Band 2 Block=1000x1 Type=Byte, ColorInterp=Green
Band 3 Block=1000x1 Type=Byte, ColorInterp=Blue

I can't tell about usability for compressed images and quality of subsampling without making some tests.

I could not refresh my memory with the GIS editing software I mentioned by trying if it really is so speedy. I did find program which is one single .exe file with an amazing file size of 600 MB but it appeared to be a 16-bit Windows program and I could not run it with my current computer. I remember that we did use both tiff files and Erdas LAN format which is probably something as simple to read as BIL and tiffs with one scanline per block are.

-Jukka Rahkonen-


Cheers
Andrea

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Ing. Andrea Aime
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