[GRASS-user] Two General Questions

[Rich Shepard]

On Sat, 13 Feb 2010, Markus Neteler wrote:

> While the second edition was written for GRASS 5.x, the 3rd edition is for
> 6.3 and later. We changed/updated about 60% of the content. Perhaps your
> library can get it for you.

Markus,

   The chapter on GRASS in the software section of the geomorphometry book is
excellent and slightly less current (version 6.2). The explanation of the
appropriate uses of the various hydrologic modules is particularly helpful;
you should extract that portion and make it available on the wiki.

   This brings up a topic that I'd like see addressed. There are a number of
GRASS users like me who are not in academia with a research focus on
algorithms or coding. We application users appreciate the efforts that have
been poured into GRASS over the past dozen or so years since I first started
to use it. But, we're not intimately familiar with the internals or the
mathematical foundations. Many of the questions I've posted on the mail
list, along with those of others, could have been answered by more attention
to the needs of those of us who apply GRASS modules without the insights
that you and other developers have. Perhaps a valid analogy would be using a
word processor to write documents without knowing the internals of the word
processing application.

   There's a lot of useful and clear explanation of how to use various GRASS
modules for predicting erosion. I'd like to see the same detail on
hydrologic and hydraulic modeling. There are many available modules
(r.basins.fill, r.carve, r.drain, r.fill.dir, r.flow, etc.) and it would be
helpful when starting (or getting back to) using GRASS to have documented
in what situations each is most appropriate. There are several that appear
to take different approaches to the same output map. Others, like r.topidx
and r.terraflow, seem to produce two distinct output maps. The former
calculates the topographic wetness index, the latter the topographic
convergence index. Is the TCI related to the tangental curvature?

   The details on computational choices and algorithms in the man pages are
invaluable. I'm suggestion that there be equal attention to the appropriate
applications of each one and, perhaps, guidance on interpretation. The man
pages are not the best place for this, the wiki is.

   The above is a suggestion that can flatten the learning curve for those
not intimately familiar with the application of GRASS. And, in my case, it
turns out that much change in terrain and hydrologic modeling has occurred
since I finished my academic career (a _long_ time ago) and my work has not
involved such modeling until this most recent project. I hope to build on
this renewed knowledge, but that all depends on the market.

Rich