jmorton@newton.Berkeley.EDU (John Morton) (09/22/88)
I am interested in sources for U.S.G.S. Digital Elevation Models
other than the Nat'l. Cartographic Information Center. I understand that
in some sense or other the data is in the public domain, although I am
also painfully aware that the N.C.I.C. charges $100 per 7.5 min. model
(points spaced at 30 m.), plus tape charge.
I have two other questions for those who have experience with
D.E.M.'s:
1) What is involved in concatenating adjacent models? The D.E.M.
Data Users' Guide says that the array rows are not necessarily of equal
length, and that a data set represents a quadrilateral with non-
parallel sides! So how do you match the edges? I would like to come up
with a rectangular array which crosses model boundaries.
2) I have worked with an array obtained several years ago by
a friend who ordered every 7.5 min. quad available for the Sierra
Nevada at the time. It has some conspicuous striations running at ~8 deg.
to the E-W line. My friend says this is noise that came with the data,
and that any efforts to smooth it out have resulted in too much loss of
detail for his purposes. Are the sets currently offered any better in
this regard? The N.C.I.C. in Menlo Park didn't know what I was
talking about, and I want to be sure that if I pay for something there
are no visible artifacts in the topography.
John Morton jmorton@newton.berkeley.edu
{decvax,cbosgd}!ucbvax!newton!jmorton