The Digital Geographic Information Exchange Standard DIGEST

1

• The Digital Geographic Information Exchange
  Standard (DIGEST)
• Applicability / Impacts for the
• CIP Program
• January 28, 2003

2
Outline

• Overview of DIGEST
• Standard ASCII Table of Contents
• Standard Geospatial Support Data Extensions
• CIP Mosaic Product Issues
• Potential Applicability of DIGEST to CIP Mosaic
  Exploitation Products
• Issues / Conclusions

3
Overview of DIGEST

• Primary purpose of the DIGEST is to facilitate
  the exchange of Digital Geographic Information
  (DGI) between nations
• A DIGEST Exchange Medium comprises a collection
  of DIGEST Information Packages pertaining to
  one or more Geographic Areas of Interest.
• Contents of a DIGEST Exchange Medium
• Single Standard ASCII Table of Contents (SATOC)
• Multiple DIGEST Information Packages
• Multiple non-DIGEST Geo Data Files (ex., DTED)

4
Standard ASCII Table Of Contents

• Purpose of Standard ASCII Table of Contents
  (SATOC)
• Provide details about contents of a DIGEST
  Exchange Medium
• List and provide direct access to the different
  Information Packages
• SATOC stored as a separate file
• File named SATOC.TXT
• Plain ASCII text file
• Supports multiple datasets in a row/column mosaic
• A Mosaic is a set of frames of uniform size
  organized in rows and columns, designed to cover
  an entire Geographic Area of Interest.
• Does uniform size mean pixels or geographic area?
• Assume that overlap of frames is acceptable

5
Standard ASCII Table Of Contents

• Supports multiple datasets in a row/column mosaic
• Each dataset (frame) stored in a separate file
• Each dataset described by a Minimum Bounding
  Rectangle (MBR)
• Minimum and maximum latitude/longitude values of
  rectangle bounding data area

(NE.lat, NE.lon)
Minimum Bounding Rectangle
Valid Frame (Image) Data
(SW.lat, SW.lon)
6
Geospatial Support Data Extensions

• The DIGEST Image Interchange Format (IIF) is
  based on the NATO Secondary Imagery Format
  (NSIF), version 1.0 (STANAG 4545, Edition 1)
• NSIF 1.0 is equivalent to NITF 2.1
• IIF only implements parts of NSIF/NITF which
  handle Raster (Image) or Matrix data (not Graphic
  data or Text data)
• Each IIF file is compliant with NSIF 1.0 / NITF
  2.1
• Geospatial Support Data Extensions (GeoSDEs) are
  contained within the IIF specification

7
Geospatial Support Data Extensions

• Potentially useful GeoSDEs
• GEOPS - Geo Positioning Information
• Defines absolute coordinate system (REQUIRED when
  any other GeoSDEs are included)
• Single GEOPS allowed per NITF file
• GRDPS - Grid Reference Data
• Defines location grids for non-rectified imagery
  (up to 99, but usually only 1 or 2 needed)
• Each grid can be computed at a different
  elevation
• Constant row/column spacing between consecutive
  elements within a grid
• Single GRDPS allowed in subheader
• Actual lat/lon values for each grid are contained
  in a separate image segment

8
Geospatial Support Data Extensions

• Potentially useful GeoSDEs (continued)
• REGPT - Registration Points
• Provides lat/lon values of specific pixels in the
  image
• Up to 1298 registration points
• Registration points do not have to be on a
  rectangular grid
• Format of lat/lon values is BCS-N and length of
  field is 15, which should allow up to 10 decimal
  digits of precision
• Ex ddd.xxxxxxxxxx
• BNDPL - Bounding Polygon
• Provides description of significant data
  contained in the Image Segment
• Supplies lat/lon values of points constituting
  bounding polynomial
• Same precision as REGPT lat/lon values

9
Geospatial Support Data Extensions

• Bounding Polygon

Bounding Polygon Points
Minimum Bounding Rectangle
Valid Frame (Image) Data
10
CIP Mosaic Product Issues

• ASARS-2A

Input
Output
Individual input tile corner points not preserved
2K x 2K Tiles (for Detected Data)
Corner Point Lat / Lon values available for each
tile
Valid Data
Output Product Corner Points
11
CIP Mosaic Product Issues

• SHARP (On-Demand Decompression Capability)

Flight Track
(0,0)
C

• Overlapping frames, each taken at a different
  sensor position
• Each frame contains compressed Full Res image and
  Reduced Res Thumbnail image
• Mosaic products produced from thumbnail images
• Mosaic control file maintained internal to CIP to
  support external extraction requests

R
Mosaic Segment
12
CIP Mosaic Product Issues

• SHARP (On-Demand Decompression Capability)
• Orientation of thumbnail images modified for
  generation of mosaic product, but orientation of
  compressed Full Res frames are not modified

SHARP Sensor Frame Orientation
Ground Orientation
Thumbnail Mosaic Orientation
x
(0,0)
x
(0,0)
(0,0)
D
D
C
A
B
y
A
B
A
B
y
y
C
C
D
x
To be verified when image data are available
13
Applicablility of DIGEST to CIP Mosaic Products

• Option 1 - Single NITF File
• Overview mosaic image as well as full resolution
  component images (SHARP and Global Hawk)
  incorporated into single NITF file
• Each component image stored as a separate Image
  Segment (with accompanying Subheader)
• Limit of 999 image segments per file
• Place overview mosaic in first image segment and
  add a NEW SDE to allow efficient selection of
  other component images
• Use GeoSDEs to preserve geolocation accuracy for
  ASARS-2A
• Option 2 - Separate NITF Files
• Each file (overview mosaic and component images)
  stored as a separate NITF file
• Standard ASCII Table of Contents (SATOC) file
  generated to support exploitation of component
  images

14
CIP Mosaic Control File Structure
Sync
File Length
Version
- MOSAIC_CONTROL or FRAME_GROUP
File Type
Data Type
- EO,IR,SAR
Format
- Line, Frame
Scene Number
Segment Number
Target Number
Columns in Mosaic
Rows in Mosaic
Mosaic DSR
Mosaic Control Pathname
Frame Groups
Pathname
Frame Components
Frame Group 1
Frame Group 2
? ? ?
Frame Group M
Frame Component 1
Frame Component 2
? ? ?
Frame Component N
15
Option 1 - Mosaic Control Info Mapping
Sync
File Length
Not Needed
Version
File Type
Data Type
ACFTB (SENSOR_ID_TYPE)
Format
Scene Number
ACFTB
AIMIDB
Segment Number
MSTGTA
Target Number
Columns in Mosaic
Subheader of first image segment
Rows in Mosaic
New SDE
Mosaic DSR
Not Needed
Mosaic Control Pathname
New SDE or NITF Header ( Image Segments - 1)
Frame Groups
Pathname
Not Needed
Frame Components
Frame Group 1
New SDE (Change to Image Segment )
Frame Group 2
AIMIDB
? ? ?
New SDE (If desired)
Frame Group M
NITF Header (Subheader Segment Lengths)
Frame Component 1
Frame Component 2
? ? ?
New SDE
Frame Component N
16
Option 2 - Mosaic Control Info Mapping
Sync
File Length
Not Needed
Version
File Type
Data Type
ACFTB (SENSOR_ID_TYPE)
Format
Scene Number
ACFTB
AIMIDB
Segment Number
MSTGTA
Target Number
Columns in Mosaic
Subheader of Mosaic File
Rows in Mosaic
???
Mosaic DSR
Not Needed
Mosaic Control Pathname
SATOC (NUM_DATASETS)
Frame Groups
Pathname
Frame Components
SATOC (DATASET_PATH, DATASET_NAME)
Frame Group 1
Frame Group 2
SATOC (ROW, COL in mosaic components
description)
? ? ?
Frame Group M
Not Needed
Frame Component 1
Frame Component 2
? ? ?
SATOC (Convert to MBR lat/lon values)
Frame Component N
17
Issues / Conclusions

• Standard ASCII Table of Contents (SATOC)
• Geared to indexing a collection of separate
  mosaic component files
• Minimum Bounding Rectangle positioning approach
• Requires conversion from pixel to lat/lon prior
  to frame selection
• Does not accurately describe valid image extent
  for images that are not aligned North/South
• Potentially addressed by BNDPL SDE in individual
  frame files
• Geospatial Support Data Extensions (GeoSDEs)
• REGPT SDE seems well suited to support ASARS-2A
  mosaic products