In answer to William Hargrove's comments:
GrassHoppers:
I don't really see the big deal about floating point maps and zero vs
no data problems. Multiply by 10 times the number of decimals of accuracy
you need to take care of the first problem. Shift all category values up
one notch to take care of the other.
It is simple to transform one floating-point variable into integer form. But
it is a data management and quality assurance nightmare to be handling
tens of floating point transformations, both multiplication and division.
If I build a customized research environment, now both I and the end-user
must deal with the mental gymnastics. If we wish to develop diagnostic ratios
of output variables, the confusion expands. And now try sharing these data
with S-PLUS, PCI or PV-WAVE for visualization, etc.
Shifting categories is not a solution, because the variables are continuous
scalars (not categories!), and may range from negative to positive. Thus what
had been -1 is now misinterpreted as zero, and image displays have erroroneous
"null data" holes. I have used this chewing-gum approach in the past, but at
a significant cost of my time and that of the researchers I coordinate with.
For example, if you do these shifts, you now have the overhead of kludging the
legend display, etc.
IMHO, a much more severe limitation to the current implementations of
GRASS is the current XDRIVER. The named fifo pipe technique is a kludge at
best. GRASS needs *real* X-window support, including more than 8 plane
support.
This is a legitimate concern. But at our lab, floating point and null data
limitations outweigh its importance. The user community needs to weigh in on
the competing priorities.
The people at CERL are aware of this (and even a little defensive
about it). All such imporvements take, they are quick to point out, is
time and money ...
Alas, yes.
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Greg Koerper Internet: greg@heart.cor.epa.gov
ManTech Environmental Technology, Inc. UUCP: hplabs!hp-pcd!orstcs!koerper
US EPA Environmental Research Lab
200 SW 35th St., JSB
Corvallis, OR 97333 "The 90s will make the 60s look like the 50s.
(503) 754-4490 Just ask your kids."
fax: (503) 754-4338
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