Greg Koerper greg at towhee.cor2.epa.gov
Thu Apr 15 20:43:51 EDT 1993

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 Koerper                            Internet: greg at heart.cor.epa.gov
ManTech Environmental Technology, Inc.  UUCP:     hplabs!hp-pcd!orstcs!koerper
US EPA Environmental Research Lab
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