# Presentation: 532323

## Boise N.F. Lessons Learned

- John Mootz
- APFO
- 2008 USDA Imagery Planning Meeting
- December 3, 2008

## Topics

- Flight Planning
- Image File Naming
- Photo Center File
- Color Bit Depth
- Color Band Order
- Image Rotation
- Inertial Measurement Unit
- Camera Calibration Report

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Topics not discussed

- Delivery media
- Provisioning/distribution
- Long-term storage

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Flight PlanningBackground

- Traditional film acquisition had well established flight planning process
- 9-inch squared aerial film
- North-south flights
- Footprint was based on film scale
- Endlap: 62%; Sidelap: 30%
- APFO flight planned and provided exposure stations with contract

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Government cannot “flight plan”
Each camera has unique footprint
Camera not known until after award
Flight planning requirement passed to contractor
Allows coverage optimization (based on aircraft, terrain, weather patterns, etc)

- Each camera has unique footprint
- Camera not known until after award
- Flight planning requirement passed to contractor
- Allows coverage optimization (based on aircraft, terrain, weather patterns, etc)

- Flight Planning (Con’t)Direct-digital Cameras

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Flight Planning (Con’t)Direct-digital Camera Footprints

- DMC
- 7,680 x 13,824
- 120mm/25mm

- UltraCamXp
- 11,310 x 17,310
- 100mm/33mm

- ADS-80
- 12,000 line
- 64° FOV

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Flight Planning (Con’t)Lesson Learned

- Boise project required contractor to submit flight plan for approval
- Due to the extreme terrain, originally planned for 80%/56% (block D)
- Reduced to 72%/43%
- Extra coverage increased acquisition risk and file sizes
- Sidelap/Endlap significantly impacts file sizes

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Image File NamingBackground

- Original naming convention
**	****<project code> _<image number>_<yyyymmdd>.tif**
- 	project code = project code
- 	image number = consecutively numbered value
- 	yymmdd = image exposure date
- 	Example:	614020_00001_20080827.tif

- Mod 2 naming convention
**	****<project code>_<flt line no>_<exp no>_<yyyymmdd>.tif**
- 	project code = project code
- 	flt line no = flight line number
- 	exp no = consecutively numbered value
- 	yyyymmdd = image exposure date
- 	Example:	614020_0025_0001_20080827.tif

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Image File Naming (Con’t)Lesson Learned

- Predetermined stations not possible
- Each direct-digital system has different footprint
- Need a way to index back to location
- Consistency is needed within project
- Photo Center File numbers must match
- Only one file allowed per “station”

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Photo Center FileFilm-based Acquisition

- Project Identification Code	6
- Flight Line Number*	4
- Exposure Number*	4
- Date of Exposure	8
- Time of Exposure – Local 24 Hour Clock	6
- Sensor Serial Number **	15
- Latitude (DD.DDDDD)	8
- Longitude (-DDD.DDDDD (Negative))	10
- Flight Altitude in meters at camera	8
- *Same flight line and image numbers used for file naming convention.
- .

- 	MAXIMUM NUMBER OF
- _DESCRIPTION_	_CHARACTERS IN FIELD_

**±30m accuracy**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Photo Center File (Con’t)Direct-Digital

- Project Identification Code	6
- Flight Line Number*	4
- Exposure Number*	4
- Date of Exposure	8
- Time of Exposure – Local 24 Hour Clock	6
- Sensor Serial Number **	15
- Latitude (DD.DDDDD)	8
- Longitude (-DDD.DDDDD (Negative))	10
- Flight Altitude in meters at camera	8
**Number of GPS Satellites Acquired****	****2**
**Position Dilution of Precision (PDOP)****	****3**
**IMU omega value (Radians)****	****10**
**IMU phi value (Radians)****	****10**
**IMU kappa value (Radians)****	****10**
***Same flight line and image numbers used for file naming convention.**
****If digital camera has more than one sensor head please use the camera serial       number****.**

- _Example_:
- 614020,25,1,20080827,130755,12345678,42.71936,-23.41498,7048.63,5,1.5,.0001358,.01073000,-.8732658

- 	MAXIMUM NUMBER OF
- _DESCRIPTION_	_CHARACTERS IN FIELD_

**±5m accuracy**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Photo Center File (Con’t)Lesson Learned

- PCF is critical for spatial positioning
- GPS/IMU data needed
- 5-decimal place lat/lon is only accuracy to approximately 1m

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit DepthBackground

- Most digital cameras acquire imagery at 12 or 14-bits per color
- Graphic file formats use bytes (8-bits) to store each pixel color
- Bit depth determines the number of possible “shades” per color
- 256 shades for 8-bit (2^8)
- 65,536 shades for 16-bit (2^16)

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t) GIS vs Remote Sensing

- GIS users:
- Want “pretty picture”
- 8-bit, color balanced image
- Remote Sensing users:
- Want unmodified radiometric data
- No data loss
- 16-bit, unstretched image
- Contradictory needs

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Histogram Basics

- A graph showing the relative distribution of various tonal values in an image. The histogram shows the number of “dark” values on the left and “bright” values on the right. Its purpose is to show the distribution of tone throughout an image.

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Histogram Examples

**DARK IMAGE**

**FLAT IMAGE**

**LIGHT IMAGE**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)12-bit Storage in 16-bit File Format

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Unstretched Image

**Unadjusted Boise NF image displayed in ArcMap **

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Histogram Stretching 

**Stretch**
**(LUT)**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Histogram Comparison

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Image Options

- Do nothing
- ArcMap does not automatically apply histogram stretch
- Pre-stretch histogram
- Stretching is irreversible
- Data loss may impact RS users
- Create an “AUX” file
- Contains statistic information

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Histogram Stretching

**Linear**

**Non-linear**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Bit Depth (Con’t)Lesson Learned

- Unprocessed imaging will look “black” without stretching
- AUX file will resolve issue in ArcMap
- More than one method of “stretching” histogram
- Users need to be educated

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Image RotationSensor Attitude 

- Long dimension of image is flown parallel with a/c wings
- Reduces number of flight lines (lowers acq cost and risk)
- “Upper left” corner of image may not be the northwest point

- Source: Aero-Metric

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Image Rotation(Con’t)North-South Flight Lines

- Image Rotation(Con’t)North-South Flight Lines

**North bound**

**South bound**

**DMC saves images in “portrait” mode**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Image Rotation(Con’t)Importing Unprocessed Imagery

- RS software will not “auto” rotate image using the GeoTIFF/TFW rotation information

**ArcMap**

**Socet Set**

**North bound**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Image Rotation(Con’t)Lesson Learned

- RS software requires applying the GPS/IMU data to display north up
- Cannot “flip” image because correct image/IMU orientation would be lost
- End users will have to understand that each camera manufacturer may save image data differently

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Band OrderDisplaying Multispectral Imagery

- Remote sensing software assumes ”satellite” band order when opening multispectral imagery

**ArcMap**

**ERDAS**

**4-band NAIP imagery**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Color Band Order (Con’t)Lesson Learned

- No issue with 3-band imagery
- GIS software applications act consistently with photographic applications
- One set of users will have to adapt
- RS users are more “experienced” with band order
- Long-term consistency is important

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Inertial Measurement UnitGeneral Concept

- An IMU works by detecting the current rate of acceleration, as well as changes in rotational attributes, including pitch, roll and yaw. This data is then fed into a computer, which calculates the current speed and position, given a known initial speed and position
- A major disadvantage of IMUs is that they typically suffer from accumulated error.

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Inertial Measurement Unit (Con’t)IMU Errors

**Dead Reckoning**

**Est Final Error**

**Reverse filtering**

**Kalman Filter**

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Inertial Measurement Unit (Con’t)Differential GPS vs IMU

**	****	**

|  | Advantage | Disadvantages |
| --- | --- | --- |
| DGPS | • High accuracy of position and velocity estimation
• Time-independent error model | • Low bandwidth
• Satellite shading (dropouts)
• Slow ambiguity resolution |
| IMU

 | • Full 6 DOF solution
• Continuous data acquisition
• Self-contained (no dropouts) | • Drift - solution errors grow over time |
| INS /
DGPS | • Combine all advantages of both
systems
• Redundant and complementary data (both systems’ errors are separately observable)
• Navigation through GPS outages
• GPS fixes allow INS error estimation | • No significant limitations
 |

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Inertial navigation system starts from a known position (i.e. airport)
Current position is updated by IMU
Drift error is corrected with GPS
Post-processed for backward solution

- Current position is updated by IMU
- Drift error is corrected with GPS
- Post-processed for backward solution

- Inertial Measurement Unit (Con’t)Combining IMU & ABGPS

- Source: Applanix Corp

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Inertial Measurement Unit (Con’t)Lesson Learned

- Must rely on contractor’s to accurately post-process data
- No method for inspecting accuracy
- CORS/Base stations impact accuracy
- Processed GPS/IMU data very important for ortho production
- No industry standard for text data
- Contract specification will have to state what software end user is using

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Camera Calibration ReportLesson Learned

- No report similar to film-based USGS camera calibration report
- Must rely on manufacturer’s calibration report
- No “fiducial marks”
- Frame-based cameras have multiple sensors
- DMC has 8 sensors/2 lens lengths

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Summary

- Intended use of imagery significantly drive requirements
- Need to standardize products for consistency
- End users need basic level of education

- 2008 USDA Imagery Planning Meeting

- 12/3/2008

## Questions

- 2008 USDA Imagery Planning Meeting

- 12/3/2008