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National Imagery Transmission Format Standards (NITFS) Compliance Test and Evaluation (CTE) Facility |
How to Develop A New TRE
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OVERVIEW |
| To serve a varied group of users exchanging
multiple types of imagery and associated data, the NITF strives to possess
completeness, simplicity, minimal overhead. In the file header and image subheader, a physical separation for
"registered tags" and "controlled tags" between "user defined" and
"extended" fields, is no longer required in NITF 2.1. Either type of
tagged record extension (TRE) may appear
in either area, thus doubling the space available to contain TREs.
Removal of this NITF 2.0 restriction allows registered tags to
appear in symbol (graphic) and text subheaders that do not have user
defined fields. As in NITF 2.0, TREs must be placed in the
subheader of the segment for which the extension pertains or in the
file header if the extension pertains to multiple segments or to the
entire file. This page contains TRE format, TRE placement, and
general requirements.
(See Appendix C,
NITFS Standards Compliance and Interoperability Test and evaluation
Program Plan Version 2.0, (N-0105)). |
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TRE FORMAT |
| Each TRE consists of three required fields:
TRETAG (6 byte unique extension identifier), TREL (length of
extension in bytes), and TREDATA (data according to the
specification of the extension). |
Registered and Controlled TRE Format.
(TYPE "R" = Required, and "C" =
Conditional) |
| FIELDS |
NAME |
SIZE |
VALUE RANGE |
TYPE |
| RETAG or CETAG |
Unique Extension type
identifier. This field shall contain a valid
alphanumeric identifier properly registered with the ISMC. |
6 |
BCS-A |
R |
| REL or CEL |
Length of REDATA fields.
This field shall contain the length in bytes of the data
contained in REDATA or CEDATA. The TRE length is 11
plus the size of the REL field or the CEL field. |
5 |
BCS-N (00001-99985) |
R |
| REDATA or CEDATA where
appropriate |
User-defined data.
This field shall contain data of either binary or character
data types defined by and formatted according to user
specification. The length of this field shall not
cause any other NITF field length limits to be exceeded, but
is otherwise fully user-defined. |
† |
User-defined |
R |
† A
value as indicated in the REL field or the CEL field (in bytes).
(See TABLE A-7,
MIL-STD 2500C.) |
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TRE PLACEMENT |
- A sequence of TREs can appear in the User-Defined Header Data (UDHD)
and/or eXtended Header Data (XHD) field of the NITF file header or any segment
subheader User-Defined Data (UDHD) field and/or eXtended SubHeader
Data (XSHD) data. For NITF, 2.0 additional restrictions for placement of TREs applies.
Controlled extension (CE) must appear in the XHD field of the NITF file header or in the
XSHD file for any standard data type data item in the file.
- A sequence of TREs can also appear in a TRE_OVERFLOW DES. This
condition will be identified by the three byte numeric overflow field of the UDHD, XHD, UDID,
IXSHD, SXSHD, or TXSHD field containing the sequence number of the Data Extension Segment (DES) into which the tags are
placed. For NITF 2.0, CEs may appear in CE DES. REs may appear in
a RE DES.
For Registered Extension (RE):
- When the RE carries data that is associated
with the file as a whole, it shall appear in the UDHD field. If the RE carries
data associated with an image data item in the file, it shall appear in the
UDID field of that specific image data item.
- REs may appear in a RE DES when sufficient space is not available
in the appropriate UDHD or UDID fields.
For Controlled Extension (CE):
- When the CE carries data that is associated with the file as a whole, it shall appear in the XHD field.
If the CE carries data associated with a standard data item in the file, it shall appear in the
XSHD field of that specific data item.
- CEs may appear in a CE DES when sufficient space is not available in the appropriate XHD or
XSHD fields.
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When the TRE carries data that is associated with the file as a
whole, it must appear in the file header, or corresponding OVERFLOW
of the file header. If the extension carries data associated with a segment in the file, it must appear
in the subheader of that segment or an associated TRE_OVERFLOW DES.
- A TRE must be included in its entirety within the specific header or subheader
field selected to contain it, or it must be placed in its
entirety in an overflow DES.
(See Paragraph 5.17.5,
NITFS Standards Compliance and Interoperability Test and evaluation
Program Plan Version 2.0, (N-0105)).
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GENERAL REQUIREMENT |
- All data in fields designated as alphanumeric (BCS-A) must be left justified and padded
with spaces as necessary to fill the field.
- All data in numeric (BCS-N) fields must be right justified and padded with leading
zeroes as necessary to fill the field.
- All required fields must be present and must contain valid data as defined in the NITFS
TRE documents.
(For more information, refer to
MIL-STD-2500C for NITF 2.1 and
MIL-STD-2500A for
NITF 2.0 implementation.) |
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Joint Interoperability Test Command
ATTN: JTF NITFS CTE Facility
P.O. Box 12798, Fort Huachuca, AZ 85670-2798
Web page comments or problems? Please forward to: JITCN@disa.mil
NITFS CTE Facility
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