photogrammetry 101
TRANSCRIPT
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)
