[GRASS-user] r.mapcalc: compare two maps [RESOLVED]

[Rich Shepard]

On Wed, 29 Mar 2017, Vaclav Petras wrote:

> As Soeren mentioned in the other part of the thread, use r.univar to get
> the statistics. Don't rely on just looking at the resulting raster map.
> There can be things like outliers which may throw the visualization off.

Vaclav,

   Here are the results of r.univar on the output of r.mapcalc "output_diff =
blocked_h_max - open_h_max":

n=140652
null_cells=71271
cells=211923
min=-1.89342188835144
max=0.00093058729544282
range=1.89435247564688
mean=-5.03205256742558e-05
mean_of_abs=5.24979771199771e-05
stddev=0.00847518705371129
variance=7.18287955953955e-05
coeff_var=-16842.4056389523
sum=-7.07768257713542
first_quartile=-7.4142e-09
median=0
third_quartile=2.60843e-09
percentile_90=7.45058e-08

   With no experience interpreting r.univar output I'm not sure what the
above tells me about the two maps. Yes, I see a small range and many null
cells, but I expect that because 4 cells on one input DEM are set about 0.6m
higher elevation than those on the other input DEM.

Rich