[GRASS-user] r.tile behaviour

[Markus Metz]

On Wed, Nov 7, 2018 at 7:06 PM Veronica Andreo <veroandreo at gmail.com> wrote:
>
> Hi Sajid,
>
> I have never used r.tile before, but checking the code [1], it multiplies
the overlap by 2, so there's why. Now guesstimating, if I set an overlap of
50, I would expect to have that overlap on both sides of the desired size
of the tiles, so maybe that's why it is doubled ?

In princliple that's correct, but not for the first and last row and column
of tiles.

In Sajid's example, the first and last row of tiles should have 725 rows
(675 + 50) and all other tiles 775 rows (675 + 2 * 50). Accordingly for
columns.

That should be relatively easy to fix.

Markus M
>
> HTH,
> Vero
>
> [1]
https://trac.osgeo.org/grass/browser/grass/trunk/raster/r.tile/main.c#L101
>
> El mié., 7 nov. 2018 a las 15:08, Sajid Pareeth (<spareeth at gmail.com>)
escribió:
>>
>> Hi all
>>
>> The r.tile module don't have overwrite flag, so if we re run the module
with different parameters but with same output prefix name, then it will
rewrite output with out warning.
>> Is this intentional?
>>
>> Another point is, if I use overlap option it adds double the overlap
cells to the output maps.
>>
>> For example in the NC location:
>>>
>>> r.info elevation -g
>>
>> rows=1350
>> cols=1500
>>
>>> r.tile input=elevation output=elev_tile width=750 height=675
>>> r.info elev_tile-001-001 -g
>>
>> rows=675
>> cols=750
>>
>>> r.tile input=elevation output=elev_tile width=750 height=675 overlap=50
>>> r.info elev_tile-001-001 -g
>>
>> rows=775 (+ 100)
>> cols=850 (+ 100)
>>
>> In the last case the rows and cols should be 725 and 800 respectively,
as it should add 50 cells as overlap to each tile? Or am I missing
something?
>>
>> Regards
>>
>> Sajid
>>
>>
>>
>>
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>
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