[mapserver-users] Transparent lines at -180 when rendering BlueMarble data

[Jason Beverage]

Hi Steve,

I thought of that too, but even the Introduction to MapServer page (
http://mapserver.org/introduction.html) uses -180 -90 180 90 to render the
BlueMarble data at full extent so that seems like it shouldn't be the case.
I'll keep on testing and see what I can come up with.

Thanks,

Jason

On Wed, Dec 30, 2009 at 11:40 PM, Lime, Steve D (DNR) <
Steve.Lime at state.mn.us> wrote:

> I wonder if it's due to differences in the extent models. GDAL uses
> edge-to-edge (I believe) meaning that the extent represents the outer edge
> of the UL and LR pixels in the image. MapServer uses a center-to-center
> model where the extent represents the pixel centers of the UL and LR pixels.
> The software itself takes these differences into account and you might need
> to as well as you compute extents. So, when you set an extent with minx at
> -180, MapServer has the center of it's left-hand edge pixels at -180, but in
> GDAL that's the left-hand edge of the left-hand edge pixels. Rounding error
> could account for the blank column.
>
> I'd convert your GDAL extent to a MapServer extent (I can help with this if
> necessary) and then chop things up based on that. Make sense?
>
> Steve
>
> ________________________________________
> From: mapserver-users-bounces at lists.osgeo.org [
> mapserver-users-bounces at lists.osgeo.org] On Behalf Of Jason Beverage [
> jasonbeverage at gmail.com]
> Sent: Monday, December 28, 2009 1:27 PM
> To: mapserver-users
> Subject: [mapserver-users] Transparent lines at -180 when rendering
> BlueMarble data
>
> Hi all,
>
> I'm using mapscript to render some blue marble data into tiles.  The issue
> I'm seeing is that occasionally I get a 1pixel wide transparent column along
> -180 at different zoom levels.  For example, if I render a 256x256 tile by
> setting the map's extent using:
> map.setExtent (-180.0, -22.5, -157.5, 0.0)
>
> I'm getting the attached image with the transparent column.
>
> The extent of the file itself via gdalinfo is -180,-90,180,90 so it does
> cover the whole world and there are no transparent pixels in the data
> itself.
>
> Thanks!
>
> Jason
>
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