[Xastir] vertical lines in hi-res geotiff orthophotography

[Kevin Ratcliff]

On Tue, Jan 18, 2011 at 12:17 PM, Tom Russo <russo at bogodyn.org> wrote:
> I would expect that this is a bug in the rendering method in Xastir, not
> a system-dependent thing (so I doubt your fresh Fedora experiment will show
> any improvement).

I did not get to my Fedora experiment yet. I did however realize that
I made a mistake in my posting: it works fine (no vertical lines) on
my Ubuntu 10.10 box. I thought I had tested it there, but apparently
not, because it works now.

> Xastir draws rectangles for each pixel using XFillRectangle, and my guess is
> that the place where it calculates the size of the rectangles is getting the
> calculation just a tiny bit off.  This is just a hunch, but most of the imagery
> that has been used in Xastir so far is far lower resolution than these, and
> it's entirely possible there's a numerical issue in the computation.  At least,
> that's what this sort of thing smells like to me just from your description.

I wonder if perhaps the screen size and resolution can contribute to
this? The (working) Ubuntu 10.10 box has a 15" monitor running
1024x768. I will attach a widescreen monitor and see if anything
changes.

> I'd like to look into it, but it would help tremendously if you would tell me
> exactly which imagery file you're looking at, say the one with the
> SAR Training Center in it.  Looks like the web site you provided has lots of
> imagery files, and I'd rather download precisely the one that you're looking at.

I think this is a direct link to the file:
http://spatialdata.iu.edu/DOQQS/local/atterbury/2010/tif/G8.zip

After downloading and unzipping, I ran rgb2pct.py with only the input
and output filenames as parameters:

rgb2pct.py G8.tif /usr/local/share/xastir/maps/G8.tif

I can upload that output file to a web site for you in a little bit
just so you are using the exact same file that I am.

Thanks for looking into this Tom!

Kevin
KB9MQU