photogrammetry 101

Photogrammetry 101

Ted Covill, CP, PPS

NEARC Spring 2015 Conference

May 11, 2015

OVERVIEW

History of Photogrammetry

What is Photogrammetry Accuracy Standards Aerial Imagery Imagery Control Analytical Triangulation Planimetric Mapping Topographic Mapping Digital Orthophotography Data Formats

HISTORY OF PHOTOGRAMMETRY

1839: First photographs were produced 1849: Aime Laussedat proved that photography could be used to produce

maps 1862: The Union Army used aerial cameras on balloons to observe the

Confederate Army 1909: Wilbur Wright takes the first aerial photo over Centocelli, Italy 1914-1945: Due to high demands on defense intelligence, great advances

were made in both Europe and the US 1942: Bausch & Lomb became the chief supplier of aerial cameras

and mapping equipment worldwide Today: Photo missions are flown by aircraft (fixed wing and helicopter) with

cameras, digital sensors and LiDAR sensors attached to the underside of an aircraft. The development of systems for producing accurate measurements has continued to advance from an aerial platform.

WHAT IS PHOTOGRAMMETRY

Photogrammetry and Remote Sensing is the Art, Science and Technology of Obtaining Reliable Information from Non-contact Imaging and Sensor Systems About the Earth and it’s Environment and Other Physical Objects and Processes Through Recording, Measuring, Analysing and Representation.

~ ISPRS

WHAT IS PHOTOGRAMMETRY (IN ENGLISH)

Photogrammetry Involves Estimating Real World Coordinates (X, Y & Z) for Ground Bases Objects in Two or More 2D Images Based on the Approximate Perspective and Location of the Sensor

ACCURACY STANDARDS

National Map Accuracy Standards (NMAS)

American Society of Photogrammetry & Remote Sensing (ASPRS) Accuracy Standards

PROJECT PLANNING

Define Project Area

Define the Accuracy Specification, Both Horizontal and Vertical

Determine Control Location Requirements

Targets vs. Photo ID

Will Airborne GPS (AbGPS) be used

AERIAL IMAGERY

Aerial Imagery: Fixed Wing or

Helicopter Traditional Film (Color

& BW) or Digital (Color & Infrared)

Stereo Coverage (60% Forward Overlap/ 30% Side Overlap)

Fly at the Proper Altitude to Insure Accuracy

Fall/Spring Flying Season (Leaf-off Conditions)

Fly at the Right Time of Day (High Sun Angle)

AERIAL IMAGERY

Types of Sensors Film Cameras Digital Sensors LiDAR Sensors

AERIAL IMAGERY – Film Cameras

Film Types Black & White Film Color Film Infrared Film

AERIAL IMAGERY – FILM CAMERAS

Commons Camera Systems

Wild RC20/30 Zeiss Top Zeiss/Jena LMK

AERIAL IMAGERY – DIGITAL SENSORS

Push Broom Sensors

Frame Sensors

AERIAL IMAGERY- PUSH BROOM SENSORS

Seamless Strip Imagery

Utilizes AbGPS and IMU

Forward, Nadir and Backward Scanning

Leica ADS80 (Push Broom)

Jena (Push Broom)

AERIAL IMAGERY- FRAME SENSORS

Individual Flight Lines with Overlapping Images

Utilizes AbGPS & IMU Microsoft UltraCAM (Frame) Z/I DMC (Frame)

AERIAL IMAGERY – ADVANTAGES OF DIGITAL SENSORS

No Need for Film (If you can find it) No Chemical Processing or

Chemical Waste No Need to Scan Negatives (No

Dust, Lint or Scratches) More Efficient Work Flow – True

Digital Throughput Improved Automated Techniques

and Processing Superior Image Quality (8 bit vs. 16

bit)

GROUND CONTROL

Establishes Reference System to tie the Imagery to Project Coordinate System

Targets (Paints “X”’s) or Photo ID (Visible Features Such as CBs, MHs & Poles)

Can Utilize Airborne GPS to Reduce Number of Control Points or Control Remote Areas

AERIAL MAPPING (PHOTOGRAMMETRY)

Analytical Triangulation Ties all the Imagery

Together Extends Control

Points Between Un-Controlled Images

Densifies the Photo Control

Validates the Accuracy of the Photo Control

Provides Setup Parameters for Imagery (Model Setups)

PHOTOGRAMMETRIC MAPPING – STEREO COMPILATION

Workstation Operators View Stereo Imagery on a High Resolution Monitor

Stereo Viewing is Achieved via an Active or Passive Viewing System

Active: Stereo Pair Images are Alternately “Flashed” on the Monitor. The Left or Right Image is Synced with the Left or Right Lens of the Glasses

Passive: Both Images are on the Monitor Simultaneously. Stereo View is Achieved with Polarized or Anaglyph (Red Blue)

PHOTOGRAMMETRIC MAPPING – STEREO COMPILATION

Workstation Operator Utilizes a 3D Cursors Called a “Measuring Mark”

The Operator can Move the Measuring Mark Through 3D Space

To Digitize an Object, the Operator Places the Measuring Mark on the Feature and Digitizes the Feature

X, Y, Z Coordinates are Recorded Along With Appropriate Level/Layer

PLANIMETRIC MAPPING

All Planimetric/DTM Data Collected in 3D from the Imagery

Data is Collected on Specific Layers (Buildings, Pavement, Hydro etc.)

Mapping Should be Done at the Proper Scale (Project Dependent)

Final Data Delivered to Clients Specifications

TOPOGRAPHIC MAPPING

Digital Terrain Model (DTM)

DTM comprised of Mass Points & Break Lines

Break Lines (Hard or Soft) Indicates Either a Natural or Man-made Change in the Terrain

Mass Points are used to supplement Break Lines

Mass Points are Placed at High & Low Areas

TOPOGRAPHIC MAPPING

Contours Old School – Ground

Was Traced at a Constant Elevation by the Photogrammetrist. Spot Elevations were Measured in areas where Contours were far apart.

Current Process – Contours Computer Generated. A TIN is Created from the DTM and the Contours are Threaded Throughout the TIN

DIGITAL ORTHOPHOTOGRAPHY

Digital Orthophotography Digital Imagery with Spatial Intelligence Combines Imagery with AT and DTM Hybrid Map. Can be used as a

Backdrop with Mapping Data

DATA FORMATS

AutoCAD (.dwg & .dxf)

MicroStation ESRI Geodatabase XML Standard or Custom

ASCII Formats LAS Raster (GeoTiff, SID,

JP2)

QUESTIONS?

Ted Covill, CP, PPS508 248 1970

ted.covill@wspgroup.com

April 30, 2015