elevations , slopes and aspect

[Darrell McCauley]

Harri Kiiveri (harrik at per.dms.csiro.au) writes on 2 Nov 93:
>I want to compare different methods for computing DTM's slopes and aspects
>from unequally spaced data . Does anyone have any data for which elevation
>slopes and aspects are known ? Failing that what about suitable test functions
>from which these things could be calculated ?

your best bet here may be to sample an analytical function.
Helena and friends have used a function proposed by Franke's
(1982) "Scattered data interpolation: tests of some methods,"
Math. Comput. 38:181-200.

I will be doing something similar: comparing elevation values (only) for
s.surf.tps, perhaps a kriging method or two, Akima's method (ACM 526,
maybe with enhancements proposed by Pruesser), and Pruesser's
ACM 684. The latter two, from Trans. on Math. Software (TOMS),
are currently being implemented for GRASS (s.bissf & s.c2grid). 
Also, one kriging program is partially written (s.okrig). None of 
s.bissf, s.c2grid, or s.okrig are quite ready for public consumption.
When they are, I will announce their availability on this list.

oh, BTW, my application is soil sensor data (particularly, organic
matter), not actual elevation.

--Darrell
James Darrell McCauley, Purdue Univ, West Lafayette, IN 47907-1146, USA
mccauley at ecn.purdue.edu, mccauley%ecn at purccvm.bitnet, pur-ee!mccauley
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