[gdal-dev] Setting the noData flag in a GeoTIFF

[Jonathan Moules]

Hi Jukka,
Good point. In fact, that's one of the reasons I want to set the noData
flag. I figure when compressing hopefully the compressor will see that it
is "noData" and will treat it differently from the way it would an actual
value (which results in things like your mentioned 255,255,254) so I won't
get the white-border-effect. I guess I'll find out if/when I get to that
point.

Cheers,
Jonathan




On 4 December 2013 06:58, Jukka Rahkonen <jukka.rahkonen at mmmtike.fi> wrote:

> Jonathan Moules <jonathanmoules <at> warwickshire.gov.uk> writes:
>
> >
> >
> >
> > Hi Even,
> > That worked great.
> > It figures that I'd tried about 6 different permutations, including a few
> without "-hidenodata"; but none of them was the right one it seems.
> >
> >
> > It's no problem recreating the tifs as they're small test tifs that takes
> a few seconds to process.
> >
> > Many thanks!Jonathan
>
> Hi,
>
> Be warned that the result may not be what you believe. You are compressing
> to jpeg and as a lossy method it does not store constant pixel values for
> the whole nodata area. If 255-255-255 pixels are nodata values you will get
> also pixels like 255-255-254 here and there and they will not be
> transparent
> in applications. That may not be a problem for you if you combine
> rectangular images with full of data into a mosaic but if you warp images
> one by one into another projection so that they will get rotated and then
> want to use the warped images side by side you would see that the
> overlapping areas look bad.
>
> -Jukka Rahkonen-
>
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