[GRASSLIST:4594] Interpolating DEMs with r.surf.spt

[Bruce Saunders]

Hello,

I want to analyze landforms and watersheds in the southeastern US 
using 7.5 min USGS quads.  10 m DEMs are available for most but 
not all of the analysis area, so I am thinking about using GRASS's 
s.surf.rst module to create 10m DEMs from 30m DEMs of the missing 
quads.  The missing quads cover about 20-25% of 1 section of the 
analysis area; very few quads are missing from the other 9 sections.

My first question is, does this sound like the best strategy 
to produce a consistent DEM using standard GRASS modules?

If so, my second question is this:  which 7.5 min quads should 
I use to generate new 10m DEMs?  

I could run r.surf.rst on sites found in the missing quads (30m 
resolution) and in 30m resolution versions of adjoining quads.  I 
would then patch the new 10m DEM quads into holes in the original 
10m DEM layer without replacing any original 10m DEM quads.

I could instead run r.surf.rst on sites found in missing quads (30m 
resolution) and in 10m resolution versions of adjoining quads.  I 
would then patch all new 10m DEM quads into the original 10m DEM 
layer, filling holes plus replacing adjoining quads.

I could also run r.surf.rst on sites found in missing quads (30m 
resolution) and in 10m resolution versions of all other quads.  
This would create an entirely new 10m DEM layer.

Each method introduces potential artifacts.  I am too inexperienced to
judge which artifacts would produce the least distortion when I 
analyze landforms and watersheds.

Does anyone out there have any recommendations?

Thanks for your help,

 - Bruce Saunders