The open code of GRASS offers great opportunity for research use--but the
lack of floating point support and distinction of null data must be corrected
if the software is to fulfill this potential. The effort should begin now to
rectify this deficiency: the alternative is risk the loss of a significant
segment of the user community.
I'd like to survey opinions, suggestions on an implementation design for
adding floating point and null data (FP/ND) support to GRASS. There are
plenty of issues that need consideration--I have listed some basic
concerns below. GRASS has benefited from the participation of the user
community in various past improvements of the package. Please don't hesitate
to contribute your expertise to this net discussion.
1. What are the requirements for adequate implementation of floating point?
- single vs. double precision
- should measurement precision metadata be attached to a raster, to
truncate display values, and to be propagated to rasters derived from
the original data set
- should an integer scaling be stored concurrently to benefit rapid
display, or do the maintenance overhead and storage costs outweigh
the value
2. Is there an existing format standard (e.g. HDF) which should be adopted?
What are it's advantages, disadvantages?
3. If floating-point support were to be implemented incrementally (utility
by utility), which utilities should receive first priority for
floating-point support?
4. Are there potential problems which may be anticipated to arise in the
development of floating-point operation library functions which must
remain compatible with the existing integer-based routines?
5. Null data bit maps seem a logical solution to provide distinction from
true zeroes. Are there other techniques which should be considered?
greg
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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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