When I read the man page for the visual output map of r.watershed I see
that it's supposed to help me display results. I assume that it does this by
coloring the accumulation of surface runoff with sub-basin sizes between 0
and the threshold value.
When I display the map with d.rast.leg The color scale of the legend is
blank. There are values from zero on the top to the threshold value at the
bottom, but no colors are displayed.
How am I to interpret this map? How does 'surface runoff accumulation with
values modified for easy display' relate to minimum basin size? What are the
units of surface runoff accumulation?
When I read the man page for the visual output map of r.watershed I see
that it's supposed to help me display results. I assume that it does this by
coloring the accumulation of surface runoff with sub-basin sizes between 0
and the threshold value.
Almost right. ...with surface flow accumulation between 0 and the threshold value.
How am I to interpret this map? How does 'surface runoff accumulation with
values modified for easy display' relate to minimum basin size?
All flow accumulation values larger than the threshold value are set to the threshold value.
What are the
units of surface runoff accumulation?
Number of cells draining through a given cell. Converted to squared map units by multiplying with nsres * ewres, of the flow accumulation map of course, and first setting the computational region to match the flow accumulation map with g.region -p rast=<my_flow_acc>. -p to check that everything is all right.
Almost right. ...with surface flow accumulation between 0 and the threshold value.
Markus,
Now I understand, yet still miss the difference between the accumulation
map and the visual map.
All flow accumulation values larger than the threshold value are set to the threshold value.
Got that from the man page.
Number of cells draining through a given cell. Converted to squared map
units by multiplying with nsres * ewres, of the flow accumulation map of
course, and first setting the computational region to match the flow
accumulation map with g.region -p rast=<my_flow_acc>. -p to check that
everything is all right.
I assume that the above calculation is left for me to do; that the
module does not do the math before displaying the results. Am I correct in
my assumption?
One last point: why no color in the legend? There is color on the visual
map but not on the accompanying legend. Strange and I don't know how to fix
this.
Almost right. ...with surface flow accumulation between 0 and the threshold value.
Markus,
Now I understand, yet still miss the difference between the accumulation
map and the visual map.
All flow accumulation values larger than the threshold value are set to the threshold value.
Got that from the man page.
I forgot, the difference between flow accumulation and visual output is not only that all flow accumulation values larger than the threshold value are set to the threshold value, but also that all negative values are converted to positive values.
Number of cells draining through a given cell. Converted to squared map
units by multiplying with nsres * ewres, of the flow accumulation map of
course, and first setting the computational region to match the flow
accumulation map with g.region -p rast=<my_flow_acc>. -p to check that
everything is all right.
I assume that the above calculation is left for me to do; that the
module does not do the math before displaying the results. Am I correct in
my assumption?
Yes.
One last point: why no color in the legend? There is color on the visual
map but not on the accompanying legend. Strange and I don't know how to fix
this.
Must be a problem of d.rast.leg, no quick help from my side, sorry!
Rich Shepard wrote:
> One last point: why no color in the
> legend? There is color on the visual
> map but not on the accompanying legend. Strange and I
> don't know how to fix this.
64bit build with Cairo driver was fixed by Glynn a few days ago.
report back if it breaks with the latest SVN.
64bit build with Cairo driver was fixed by Glynn a few days ago. report
back if it breaks with the latest SVN.
Hamish,
While my server/workstation has an AMD Athlon/X2 CPU I am running the
32-bit Slackware-12.2 on it. I'll grab the latest from the subversion
repository and build it later this afternoon. Leaking kitchen sink drain
needs to be fixed first.