Problem with Graticule and polar stereographic projection

[Steve Roberts]

On Thu, 19 May 2005, Martin Weinelt wrote:

> On Thursday 19 May 2005 16:12, Frank Warmerdam wrote:
> > Steve / Martin,
> >
> > One problem with the automatic graticule generation is that it produces
> > a single polyline for each complete gridline.  If mapserver fails to
> > reproject any single point on the polyline, then the whole polyline is
> > discarded since it cannot be reliably rendered.  This means, for instance,
> > that if you show a pole, and for reasons of the math the polar location
> > is not reprojectable, then the whole line of longitude will be discarded.
> >
> > In the past, I have created actual graticule shapefiles using many small
> > line segments.  That way you just lose a wee bit of the graticule near
> > the pole or on the fringes of the reprojectable region.
> >
> > I implemented a mkgraticule.py script in GDAL for doing this, if you
> > would like to try it (gdal/pymod/mkgraticule.py in the source tree).
>
>
> Frank,
>
> I am using your your utility apps really a lot. They save me countless
> hours of quirky aml scripting. Thanks!
>
> But although we can do with workarounds or pre-projected data for
> the graticule problem, this is not the case with data dynamically retrieved
> from a data base or a WFS.
>
> Mapserver has strong evangelists in the academic realm but these institutions
> do have a demand for world mapping applications and data-base based
> mapserver installations. The issue of reprojecting for world maps in different
> aspects - imho - will come up regularly.
>
> Cheers, Martin
>

Frank,

I have in the past created my own grid shapefiles. These work fine if you
know ahead of time what your range of map scales will be and your region
of interest. But in my applications I need to support both large scale
views of the entire arctic basin down to small scale views of just a
few kilometers across. Creating shapefiles to support this start to become
a real pain. And they start to get rather large. Having a built-in grid
that automatically does this all for you is - imho - an extemely useful
feature.

Thanks for the pointer to mkgraticule.py. I was not aware this existed.

Thanks,
-Steve