[GRASS-dev] Rast3d_location2coord inconsistent behavior

[Sören Gebbert]

2014-07-20 6:10 GMT+02:00 Anna Petrášová <kratochanna at gmail.com>:
>
>
>
> 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.

Good point, i have updated the Rast3d_location2coord() function to use floor.

Best regards
Soeren

> 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
>> >
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>
>