[GRASS5] problems with [rsv].proj

[Glynn Clements]

Eric G. Miller wrote:

> I'm having problems with UTM to Albers here.  With r.proj, I get a
> message about shifting datum NAD83->NAD27 (this should be correct), but
> then it tells me the Input Map is outside the current region (this is
> incorrect).  The error occurs in bordwalk where it checks the
> boundaries.  There's a comparison between some xmin, ymin, etc. and the
> region boundaries, and it comes up that ymin is slightly larger (1E-6)
> than to_hd->north (this difference is way way below the significant
> decimal places of the projection, which isn't better than a couple
> places).  There's some subtle numerical bug in there...

If "ymin is slightly larger (1E-6) than to_hd->north" then, unless
these values have been miscalculated, that implies that the source and
destination regions almost intersect, but not quite.

IOW, if you moved the border slightly, you would get some non-null
cells in the output but, as things stand, the output will consist
entirely of null values.

[Aside: there are cases where the "border walking" algorithm won't
produce the right results (e.g. converting polar stereographic to any
cylindrical projection), but I doubt that such cases are relevant to
"real world" use.]

-- 
Glynn Clements <glynn.clements at virgin.net>