Problem with Graticule and polar stereographic projection

Martin Weinelt mweinelt at PLANIGLOBE.COM
Thu May 19 10:45:53 EDT 2005


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



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