# Presentation: 081194

## NAIP Technical Presentation

**NAIP Technical Presentation**

**David Davis & Brian Vanderbilt**
**GIS Specialists**
**USDA Farm Service Agency**
**Aerial Photography Field Office**
- _[david.davis@slc.usda.gov](mailto:david.davis@slc.usda.gov)_
- _[brian.vanderbilt@slc.usda.gov](mailto:brian.vanderbilt@slc.usda.gov)_

## File Extensions
&
 Coordinate Systems

- &
-  Coordinate Systems

## File Extensions

- File Extension Soup
- What’s a ...
**shp** - the file that stores the feature geometry
**shx** - the file that stores the index of the feature geometry
**dbf** - the dBASE file that stores the attribute information of features
- prj - the file that stores the coordinate system information
- sbn - the files that store the spatial index of the features
- sbx - the files that store the spatial index of the features
- mdb - relational databases that contain geographic information
**tif, tiff, tff**** **– non proprietary raster format compressed or uncompressed
**sid**** **– LizardTech proprietary standard compression raster format
**jpg, jpeg, jfif**** **– non proprietary standard compression raster format
**aux**** **– location where stat info about a raster is stored, including pointer to the pyramid (rrd) file, color map, histogram/table, coordinate system, transformation, and projection information
**sdw**** **– sid world file, stores location information (upper left) of sid image
**tfw**** **– tif world file, stores location information (upper left) of tif image
**rrd**** **– pyramid file created when you choose to build pyramids in a Reduced Resolution Dataset (RRD) file, with the same filename as the dataset.
**txt**** **– file containing textual information
**xml** – extensible markup language similar to html, define tags, add meaning

## Coordinate Systems/Projections

- Coordinate System – A reference system used to measure horizontal and vertical distances on a planimetric map.  A coordinate system is usually defined by a map projection...There are two types of coordinate systems: **geographic** and **projected**. Geographic coordinate systems use latitude and longitude coordinates on a spherical model of the earth's surface. Projected coordinate systems use a mathematical conversion (projections) to transform latitude and longitude coordinates that fall on the earth's three-dimensional surface to a two-dimensional surface.
- Projection – Whether you assume the earth is a sphere or a spheroid, you need to transform its three-dimensional surface to create a two-dimensional map.  This transformation is called a projection.  In simpler terms, a projection is a mathematical attempt to place what is seen on a flat computer screen at the coordinates/location of where it really exists in the three dimensional world.  Projections can be optimized to preserve shape (conformal), area (equal area), distances (equidistance), directional (true direction), or a combination of the above.
- Datums – a datum defines the position of the spheroid relative to the center of the earth. A datum provides a frame of reference for measuring locations on the surface of the earth. It defines the origin and orientation of latitude and longitude lines.
- If the earth was a perfect sphere, this would all be much easier.
- Local Datums
- On the Fly Projections in ArcMap
- Changing Projections in ArcCatalog
- Shapefiles/Geodatabases
*Actually* Reprojecting/Encoding Imagery
- Spatial Reference Data
- Order of Application
- ArcMap – Header, AUX, World Files
- ArcView – TFW First

## Color, Light, and Atmospheric Conditions

## Colors

- What is the most important color to see?
- Shades of green/red/blue?
- Depends on what you’re looking for...

## Color Samples

- NAIP Color Samples
- For Each State
- Approved by APFO Color Team
- Approved by State Coordinator/Specialist
- Forwarded to Vendor as Part of Award Package

## Color Balancing

- NAIP Contract Requires Color Balancing
- But what is your target image?
- Color adjusted/balanced image
- adds contrast, more interpretable, pleasing to the eye
- Unbalanced/raw data
- may lead to an inconsistent, patchwork CCM

- NAIP04 CCM Christiansen County, Illinois

## What is Bit-Depth?

- # of possible colors a particular pixel can hold.
- With 8 bit, each channel has 256 (2 to the 8th) different possible intensity values for each primary color, so an RGB pixel can hold 256 to the 3rd or > 16 million different colors = true color
- With 16 bit, this number is 2 to the 16th x 2 to the 16th x 2 to the 16th or 281 trillion colors
- Human eye can only discern around 10 million colors
- File Sizes

- http://www.cambridgeincolour.com/home.htm

**So, how many values are possible for a BW image that can only hold 1 bit per pixel?  What about 2 bits per pixel?**

**Notes:**
Mini Quiz Answer: 1 bit per pixel = 2 values.  2 bits per pixel = 4 values.

## Understanding Light

- http://imagine.gsfc.nasa.gov

## Understanding Light

- Four Electromagnetic Radiation (EMR) Interactions With Matter
- Transmission
- Process by which incident radiation passes through matter w/o measurable attenuation
- Reflection (spectral reflection)
- Process by which incident radiation “bounces off” the surface of a substance in a single, **predictable** manner
- Scattering (diffuse reflection)
- Incident radiation is dispersed or spread out **unpredictably** in many directions
- Absorption
- Incident radiation is taken into the medium

- Avery, Thomas Eugene, and Graydon, Lennis Berlin. Fundamentals of Remote Sensing and Airphoto Interpretation, Fifth Edition, Prentice Hall, 1992

**Who can give real world examples of each of the four interactions?**

**Notes:**
Mini Quiz Answer: Transmission = light going from an air medium to water medium with radiation being refracted accompanied by a change in wavelength and velocity.  Reflection = Sunlight reflected upwards by clouds.  Scattering = Light scattered through water vapor.  Absorption = Light absorbed by asphalt, and consequentially the asphalt gets hotter.

## Clouds

- Reflect Light (EMR)
- Absorb Light (EMR)
- Obscure View!!!
- Cloud cover and cloud shadow
- 10% Rule
- Cloud cover or cloud shadow (DOQQs)

## Atmospheric Scattering

- Visible Light
- Rayleigh Scattering (molecular)
- Caused by oxygen and nitrogen molecules
- Most influential at altitudes above 4.5 km (~15,000 ft)
- Scattering inversely proportional to fourth power of wavelength
- So, blue at .4um scattered five times as readily as red at .6um.
- Why is the sky blue?
- Mie Scattering (non-molecular)
- Important scattering agents include: water vapor, smoke, dust, volcanic ash, salt crystals, etc.
- Most influential at altitudes below 4.5 km
- Depending on factors, blue scattered more readily than red

- Avery, Thomas Eugene, and Graydon, Lennis Berlin. Fundamentals of Remote Sensing and Airphoto Interpretation, Fifth Edition, Prentice Hall, 1992

**Average flying altitude for NAIP?**

**Notes:**
Mini Quiz Answer:  This really depends on the type of camera being used.

## Atmospheric Scattering

- Visible Light
- Skylight
- Skylight is primarily blue
- Skylight prevents absolute darkness in shadows
- Haze
- Sky radiation is manifest as haze to our eyes
- Causes distant landscapes to look blue-gray
- Radiation Reaching a Sensor
- S=S(s)+S(a)
- S(a) contains no info about the earths surface and acts as a masking agent when remote sensors record info
- Most affected wavelengths are ultraviolet and blue
- Results in a bluish tint in color photos

- Avery, Thomas Eugene, and Graydon, Lennis Berlin. Fundamentals of Remote Sensing and Airphoto Interpretation, Fifth Edition, Prentice Hall, 1992

## Sun Angle

- Function of latitude, time of day/year
- Low Verses High
- Shadow
- Goal of Image
- Ex. Agricultural land verses archeological sites

- Avery, Thomas Eugene, and Graydon, Lennis Berlin. Fundamentals of Remote Sensing and Airphoto Interpretation, Fifth Edition, Prentice Hall, 1992

## Map Accuracy Standards

## Map Accuracy Standards

- National Map Accuracy Standards (NMAS)
- Revised June 1947
- Horizontal Accuracy
- For maps on publication scales larger than 1:20,000, not more than 10 percent of the points tested shall be in error by more than 1/30 inch, measured on the publication scale; for maps on publication scales of 1:20,000 or smaller, 1/50 inch. These limits of accuracy shall apply in all cases to positions of well-defined points only.

## Map Accuracy Standards

- NAIP
- Horizontal Accuracy (DOQQs & CCMs)
- All DOQQs shall have 90% of all well-defined points tested fall within the specified distance listed below to the same location identified on Government furnished baseline orthophoto control imagery.

## Map Accuracy Standards

- Service Center Agency  Data Management Plan for Ortho Imagery (NAIP)
- Horizontal Accuracy Applies to Scale
- Hardcopy plots of the compressed county ortho mosaics can be horizontally accurate to NMAS for 1:12,000 maps. Map accuracy also applies to a display scale of 1:12,000
- Why does map accuracy apply to scale?

## Map Accuracy Standards

- NAIP
- What this means to you
- Print/view a map at a larger scale than 1:12000...

- 1:40,000 Screen Capture

- 1:12,000 Screen Capture

- 1:4,800 Screen Capture

- 2004 NAIP and Certified CLU – Baker County, OR

## Map Accuracy Standards

- NAIP
- Accuracy applies to a scale of 1:12000 or 1”=1000’=304.8 meters
- So what does a 5 meter (16.4’) offset look like on a 1:12000 print? ((.0833’)X16.4’)/1000=.016393 inches or approximately 1/60”.
- A print display of 1:4800 is 1”=400’ on paper.  5 meters on a 1:4800 scale print is .04098 inches or approximately 1/25”.
- A print display of 1:1200 is 1”=100’ on paper.  5 meters on a 1:1200 scale print is .16393 inches or 1/6”.
- The data is the same, but the look of the data will vary drastically depending on scale; the reason map accuracy references a particular scale

## Replacement Imagery

- Why Imagery of the Same Location on Earth Looks Different From Year to Year
- Digital Elevation Model (DEM)
- Aerial Triangulation Solution (AT)
- Parallax
- Sun Angle
- Orthorectification
- Control
- Sensor
- Weather
- Post Processing (Film or Digital)
- Land Use/Land Cover Changes
- Image Resolution

**http://www.fsa.usda.gov/Internet/FSA_File/replacement_image_2006_updatep.pdf **

## Image Resolution

- Resolution
- What is it?
- How does it affect what is viewed?
- Increased file sizes with higher resolution
- 2m to 1m = file size x 4 (approx.)
- 1m to 1ft = file size x 9 (approx.)
- Why?  Hint...think of a square
- “Things get fuzzy when I zoom in too far”

**If I had a 1 meter resolution image and a 6 inch resolution image of the same area, all other things being equal, about how much larger would the file size of the 6 inch be?**

**Notes:**
Mini Quiz Answer: Approximately 36 times larger.

## File Sizes

- APFO Maintains the Second Largest Microsoft Database in the World
- 12.7 TB  2005

- http://www.wintercorp.com/VLDB/2005_TopTen_Survey/TopTenWinners_2005.asp

## File Sizes

**Notes:**
APFO Takes Part in the Maintenance of the Second Largest Microsoft Database in the World

## Image Compression

- What Is It?
- APFO Website
- http://www.fsa.usda.gov/Internet/FSA_File/compression_2006_updatep.pdf
- What Formats?
- MrSID (MG2 & MG3), ECW, JPEG 2000
- MG3 vs. MG2
- Lossy vs. Lossless Compression
- Compression Ratios

**Notes:**
Mini Quiz Answer: For MG3s, a large block size would result in longer image refresh times.

## Color Calibration

- Basics
- Hardware/Software system that calibrates monitors so that an image will appear the same on all monitors (monitors, printers, scanners, etc.)
- Lighting conditions, individual color perception, and other factors can still affect a calibrated system
- APFO uses Monaco Optix 1.0
- Why we sent hard copy color samples rather than digital samples to States and vendors
- http://www.cambridgeincolour.com/home.htm

## Natural Color vs. CIR

- Natural Color
- 3 band RGB
- CIR
- 3 band IRRG
- Green light shown as blue
- Red light shown as green
- NIR shown as red
- http://spatialnews.geocomm.com/features/topoimagery01/

## Natural Color vs. CIR

- What about 4 band imagery?
- IRRGB
- ArcGIS can only represent 3 bands at a time, but the digital product can produce two distinct views of the same location

**Can both film and digital cameras acquire 4 band imagery?**

**Notes:**
Mini Quiz Answer: No, only digital cameras at present can collect 4 bands.

## Questions?