[GRASS-dev] Rast3d_location2coord inconsistent behavior

[Anna Petrášová]

On Sat, Jul 19, 2014 at 6:30 PM, Sören Gebbert <soerengebbert at googlemail.com
> wrote:

> Hi Anna,
>
> 2014-07-19 19:04 GMT+02:00 Anna Petrášová <kratochanna at gmail.com>:
> > Hi,
> >
> > I have a question about Rast3d_location2coord [1]. It is casting the col,
> > row, depth values to integer like this:
> >
> > (int) col
> >
> > instead of using
> >
> > (int)floor(col)
> >
> > as a result, col = 0.1 => col = 0 and col = -0.1 => col = 0, which
> doesn't
> > seem correct to me. Any opinions?
>
> I totally agree that there should be a function that returns the row,
> col and depth as double values, so the developer can decide how to
> handle these values. Otherwise there would be no convenient way to
> determine where coordinates are located in the voxel.
>
> But i am not sure if the  integer casting is a bug, since the
> Rast_easting_to_col() /Rast_northing_to_row() docs suggest integer
> casting as conversion method. There are algorithms in GRASS that use
> only integer casting and algorithms that make use of rounding with
> floor() before casting to integer.
>
> The problem arise in case of negative column,row or depth values when
> casting to integer without rounding to an integer smaller than the
> double number. So the question is are there any chances to receive
> negative cols,rows and depths?
>
> It does not seems do to me for col and row, since in case of negative
> coordinates will west and south always be smaller than east and north,
> resulting in always positive cols and rows. And the same should be
> true for depths, unless the top is smaller than bottom.
>

Yes, but you still can get negative col, for example when looking for the
neighboring voxels of a voxel on the edge of the 3D raster. Then, the
inconsistency causes problem.

Thanks a lot for implementing Rast3d_location2coord_double.

Anna


> Best regards
> Soeren
>
> >
> > Thanks, Anna
> >
> > BTW, similar function Rast_northing_to_row from raster library returns
> > double.
> >
> >
> > [1] http://grass.osgeo.org/programming7/region_8c_source.html#l00291
> >
> > _______________________________________________
> > grass-dev mailing list
> > grass-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/grass-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-dev/attachments/20140720/590bd01e/attachment.html>