[GRASS-dev] How to: if undefined, set to NULL?

[Nikos Alexandris]

* Markus Neteler <neteler at osgeo.org> [2016-08-27 15:37:35 +0200]:

>On Sat, Aug 27, 2016 at 3:26 PM, Nikos Alexandris
><nik at nikosalexandris.net> wrote:
>> While modifying i.rgb.his,
>>
>>    if (chroma == 0.0) {
>>
>>        saturation = 0.0;
>>
>>        /* undefined -- (how to) set to NULL? */
>>        hue = 0.0;
>>
>>        rowbuffer[0][sample] = (FCELL)hue;
>>        rowbuffer[1][sample] = (FCELL)intensity;
>>        rowbuffer[2][sample] = (FCELL)saturation;
>>    }
>>
>>
>> I'd like to set hue to NULL, whenever the condition is met. How do I do
>> that?
>>
>>    hue = NULL;
>>
>> does not work.
>
>No, it is done withRast_set_null_value()
>
>Something like:
>
>    for (row = 0; row < nrows; row++) {
>        G_percent(row, nrows, 5);
>        for (col = 0; col < ncols; col++) {
>            cell_buf[col] = bas[SEG_INDEX(ba_seg, row, col)];
>            if (cell_buf[col] == 0)

>                Rast_set_null_value(&cell_buf[col], 1, CELL_TYPE);

Alright, that is:  anything that `&cell_buf[col]` points to, set the
number of values `1` to NULL.

I need a few more examples to understand.  What is the "number of values"?
Could it be a series of multiple values?

Nikos


>        }
>        Rast_put_row(basin_fd, cell_buf, CELL_TYPE);
>    }
>
>(random example, taken from r.water.outlet/main.c)
>
>HTH,
>Markus

-- 
Nikos Alexandris | Remote Sensing & Geomatics
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