[GRASS-dev] [GRASS-user] compare a DCELL and FCELL question
dustming at gmail.com
Sun Jan 24 06:51:08 PST 2021
Hi Markus and Micha
I am just trying to find grids have the same values in these two
rasters, I will try the threshold approach.
Markus Neteler <neteler at osgeo.org> 于2021年1月24日周日 上午6:58写道：
> Hi Ming,
> On Sun, Jan 24, 2021 at 10:49 AM ming han <dustming at gmail.com> wrote:
> > Hi Micha
> > Many thanks for your reply.
> > Here is the command I am using:
> > if(float(cat1_acc_riv) == float(cat1_minacc), str_r, null())
> > The str_r is a CELL raster. the result is different when I change
> it to:
> > if(int(cat1_acc_riv) == int(cat1_minacc), str_r, null())
> Note that numerical "equality" is better tested with a threshold test
> against the map pixel difference.
> As the threshold, we use GRASS_EPSILON which is defined as 1.0e-15.
> Hence the test needs to be implemented in a different way, i.e. by
> using an epsilon.
> Essentially something like this:
> if(fabs(map_A - map_B) <= 1.0e-15, ... )
> In your case (untested):
> r.mapcalc diffepsilon = if( abs( map_A - map_B) <= 1.0e-15, str_r , null())
> See related discussions here: ,  and elsewhere.
>  Comment by Glynn: https://trac.osgeo.org/grass/ticket/2854#comment:9
>  Comment by Glynn:
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