Summary

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	File:     ddfread.icn

	Subject:  Procedures for reading ISO 8211 DDF files

	Author:   Gregg M. Townsend

	Date:     June 26, 2000

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   This file is in the public domain.

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	These procedures read DDF files ("Data Descriptive Files",
	ISO standard 8211) such as those specified by the US Geological
	Survey's "Spatial Data Transfer Standard" for digital maps.
 	ISO8211 files from other sources may contain additional data
	encodings not recognized by these procedures.

	ddfopen(filename) opens a file and returns a handle.
	ddfdda(handle) returns a list of header records.
	ddfread(handle) reads the next data record.
	ddfclose(handle) closes the  file.

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	ddfopen(filename) opens a DDF file, decodes the header, and
	returns an opaque handle for use with subsequent calls.  It
	fails if any problems are encountered.  Instead of a filename,
	an already-open file can be supplied.

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	ddfdda(handle) returns a list of records containing data
	from the Data Descriptive Area (DDA) of the file header.
	Each record contains the following fields:

		tag	DDR entry tag
		control	field control data
		name	field name
		labels	list of field labels
		format	data format

	The records may also contain other fields used internally.

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	ddfread(handle) reads the next data record from the file.
	It returns a list of lists, with each sublist containing
	a tag name followed by the associated data values, already
	decoded according to the specification given in the header.

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	ddfclose(handle) closes a DDF file.

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This file is part of the (main) package.

dda_list(p)

ddf_binn(n)

 binary value of n bytes

ddf_dtree(format)

ddf_fcrack(s)

ddf_int(cs)

 delimited integer

ddf_intn(n)

 integer of n digits

ddf_oneof(tabproc, moveproc, quantum)

ddf_rdata(f, h)

ddf_real(cs)

 delimited real

ddf_realn(n)

 real of n digits

ddf_repeat(lst)

 repeat sublist to EOR

ddf_rhdr(f)

ddf_str(cs)

 delimited string

ddf_strn(n)

 string of n characters

ddfclose(handle)

: close DDF file

ddfdda(handle)

ddfopen(fname)

: open DDF file

ddfread(handle)

: read DDF record

ddf_dde(tag, control, name, rep, labels, format, dlist)

 data description entry

ddf_decoder(proc, arg)

 field decoder record

ddf_header(hcode, dlen, ddata, tsize, lsize, psize, s)

 DDF header information

ddf_info(file, header, dlist, dtable)

 basic DDF file handle