Thank you for the information about trac, I didn’t know this software, but it could be useful!
I tried redoing the calculations without rounding. The results are closer to the results obtained with r.volume (only tens of meters of difference, instead of thousands), but they are not the exact same. I think it is because GRASS rounds the results itself (for the nesres and ewres for instance), so it is not possible to have the exact same results.
Maybe r.volume is more precise because there are no intermediate results.
Marion
De : “Moritz Lennert”
A : marion-brunet@sfr.fr,“grass-user”
Envoyé: lundi 16 juillet 2018 11:02
Objet : Re: [GRASS-user] calculate the volume of a DEM with r.volume
On 15/07/18 13:52, marion-brunet@sfr.fr wrote:
Hi,
Thank you for the clarification on the clumps, it makes more sense for
me now.However you said :
“Ideally, the clump option of r.volume should be optional. You could file
an enhancement wish on trac for that.”But I don’t really understand what you mean by “an enhancement wish on
trac for that”, could you explain it a bit more ?
Yes, sorry, I understand that this is not clear language for someone new
to the community. trac is the software we use for bug ticket management,
as technical wiki and it allows you to browse the source code [1].
Whenever you detect a bug, or you wish to see an enhancement to GRASS
GIS, you can file a ticket on trac. This gives a more solid existence to
you wish as bugs or wishes declared in messages sent to the mailing list
often get lost in the mass of mails.
In order to be able to file a ticket you need a OSGeo userid [2].
I tried doing both r.volume and multiplying the sum by the cell size,
and I have approximately the same results, but there a are some little
differences. I think it is because, with the second method, I rounded up
the results I had, because there were too many digits, so I might I lost
some precision in my results.
That is quite possible. Have you tried without rounding ?
Moritz
[1] https://trac.osgeo.org/grass
[2] https://www.osgeo.org/community/getting-started-osgeo/osgeo_userid/