2019 NYSAPLS Conf>

Fundamentals of Photogrammetry for

Land Surveyors

George Southard

GSKS Associates LLC

George Southard:

Master’s Degree in Photogrammetry and Cartography

40 years working in the mapping industry

Owner – GSKS Associates LLC

“Consulting for the Geomatics Profession”

Introduction

data processing

using the science of

Photogrammetry

Remote Photogrammetry

”The science or art of obtaining reliable

measurements by means of photographs.”

”Photogrammetry is the art, science, and

technology of obtaining reliable information

about physical objects and the environment

through the processes of recording, measuring,

and interpreting photographic images.”

(ASPRS, 1980)

Definitions:

Analog Photogrammetry

Using optical/mechanical/electrical instruments, to perform measurements from images printed on paper, film or glass, thus creating stereographic views of the image space for the purpose of 3D measurements.

Analytical Photogrammetry

Using equipment similar to those used in analog photogrammetry but which have computer/electronic components added for more efficient measurement of photographic images. Computer software programs are also a key element in these operations.

Digital or Softcopy Photogrammetry

The performance of photogrammetric operations using digital rather than hardcopy images. This work is accomplished primarily using computer, monitors, and a specially designed mouse along with sophisticated software.

Definitions:

• Photogrammerty• The Science of making maps from stereo imagery

o Stereo (3D) Imaging

o Ground Control (reference points, GPS, GNSS)

o Aero-Triangulation (georeferencing)

o Stereo Compilation

o Topographic Mapping

o Planimetric Mapping

o 3D Point Clouds

o Orthophotography

Key Technologies and Terms

History

Origins of Remote Sensing

First photographs taken in 1839

Remote sensing began withaerial photography

A brief history of Photogrammetry

1858 Gasper Felix Tournachon "Nadar" takes photograph of village of Petit Bicetre in France from

a balloon.

Paris by Nadar, circa 1858

A brief history of Photogrammetry

City of Boston by Black and King (1860), from hot air balloon

A brief history of Photogrammetry

A brief history of Photogrammetry

Major developments in aerial photography – WW1

A brief history of Photogrammetry

After the war the technology was in place to begin large scale aerial surveys

A brief history of Photogrammetry

Foundational Principles

Photogrammetric Fundamentals

First Assumption: the photo image is a flat planar surface

Second Assumption: There are planar distortions in all photo images:

- Distortions come from two sources

1) the camera platten for film or the CCD platten for

digital images

2) the camera lens(s)

Photogrammetric Fundamentals

Known constants and variables…..

Photo Orientation

Six positions of orientation are needed to georeference each photo

Ω Omega – Yaw Φ Phi – Pitch Κ Kappa - Roll

x – Longitude y – Latitude Z - Elevation

•Over lap about 60%

Aerial Photography -Stereo pair

•Over lap about 60%

Precisely controlled image capture…..

Types of Photogrametry

Photogrammetric Types from Applications Point of

View (d is distance from camera to object)

▪ Close Range Photogrammetry d<50 m

▪ Aerial Photogrammetry 50m>d<15km

▪ Space Photogrammetry d = 300 km+

Photogrammetric Types

Close Range (terrestrial) Photogrammetry

Close Range (terrestrial) Photogrammetry

Aerial Photogrammetry

Space Photogrammetry

❖ Extraterrestrial pictures taken from space-based cameras

Photogrametric Imagery

Types of Images

• Panchromatic, Black & White, Grayscale

• Color - Red Green Blue (RGB)

• Multispectral (RGB + Infrared)

• Hyperspectral

Introduction

Sensitive to

light in the

400-680nm

range

Panchromatic Image

Black and white Image

Grayscale Image

False Color composite image

True Color composite image

Types of photographs (categorized by tilt)

• Vertical - camera axis as nearly vertical as Possible

• Oblique - camera axis intentionally tilted• Low Oblique

• High Oblique

Types of photographs (categorized by tilt)

Vertical - Aerial Photo

❖ Mainly used for mapping

Low oblique (no horizon)

❖Seldom used for mapping

Low Oblique – Aerial Photo

• Horizon line in the

photo

• Typically used for

3D city modeling

High Oblique – Aerial Photo

• Maps are based on parallel projection while photo has central projection

• Maps have a unique scale. Photo scale varies depending on terrain relief and degree of radial distortion

Characteristic of a Map vs a Photo

Aerial images are not maps!

Image Acquisition for photogrammetric mapping

Image Acquisition

Precisely controlled image capture…..

Precisely controlled image capture…..

• Photos taken in parallel flight strips

Image Acquisition

• Each successive photograph overlap previous photo

Image Acquisition

Ground Control

Types of Ground Control Points

Types of Stereo Model control layout

Full Stereo Model

Control

Stereo Model Control for

Aero-triangulation

Types of Stereo Model control layout

Full Stereo Model Control – with Aero-triangulation

Ground Control Point Planning

Aero-Triangulation - (georeferencing all images for a unified

block of ground control positions and tie points)

Types of Stereo Model control layout

Photogrammetric Instruments

• MULTIPLEX MODEL SKETCH

Direct Optical Projection Stereo plotters

Kelsh – Optical/ Mechanical Stereoplotter

1930s to 1970s

Direct Optical Projection Stereo plotters

Wild Heerbrugg A8–Analogue Optical Mechanical Stereoplotter

1960s to 1980s

Direct Optical Projection Stereo plotters

• Wild BC2 analytical stereo-plotter.

Analytical Optical/Electronic Stereoplotter

1980s – 1990s

Direct Optical Projection Stereo plotters

Digital Softcopy Stereoplotter

1990s - Present

Softcopy (digital) Stereo plotters

Wild C2 - 1927

Wild RC5 - 1944

Wild RC30 & Zeiss TOP15 – 1980s

3D Aerial Film Cameras

Large Format

Medium Format

Small Format

RGB and IR≥200 MP

RGB or IR60 - 100 MP

RGB or IR10 – 20 MP

Imaging Cameras for Manned Aircraft

High Quality Photogrammetric Mapping – Calibrated Lens Distortion, Mid-

Exposure Pulse, Fixed Focal Length

Medium Quality – Photogrammetric Mapping, Lens characterization, no MEP

Imaging only, no photogrammetric mapping, no lens correction

Imaging Cameras for Unmanned Aircraft

Canon S100

12 MP

Horizontal RMSE =

6.4 cm

Vertical RMSE =

14.0 cm

Sony NEX-5

16 MP

Horizontal RMSE =

1.3 cm

Vertical RMSE =

1.9 cm

Does camera choice effect accuracy?

Camera Sensor Dimensions

(mm)

Rows x Columns (pixels) Pixel Area (μm2)

Canon S100 7.5 x 5.5 4000 x 3000 (12MP) 3.4

NEX-5R 23.4 x 15.6 4912 x 3264 (16MP) 28.8

The light collected is proportional to the sensor pixel area. Note

that the NEX has 8 ½ times the area of the Canon – this is a huge

difference!

Photon noise varies as the square root of the image signal, so

collecting more light results in proportionally less noise, i.e. a

higher signal-to-noise ratio is achieved.

Higher signal-to-noise means more sensitivity to low-light

situations, and broader dynamic range.

Sensor Size vs. image noise

Significant

Noise

Poor Conformance

Noise from Cannon S100 images

Image Noise

Noise from NEX-5R Images

Low

Noise

High Conformance

Image Noise

Focal length is highly

correlated with vertical scale

and accuracy

Precise focal length cannot be

established for zoom lenses,

even if the zoom feature is

disabled.

Focal length calibration

• Consumer cameras do not have a Mid-Exposure Pulse

(MEP)o Real Time Kinematic GNSS

o One must know the exact correlation of each photo center to the GNSS position at

time of exposure

o Common practice is to use the camera flash signal to create a MEP with

modifications to the electronic circuitry

• Consumer cameras do not offer stock fixed focus lens

optionso Requires special lenses (which are expensive or not available for many consumer

cameras.)

Other Issues….

• Airborne LIDAR: Manned Aircraft

Wide Area Mapping500-800 kHz pulse

rate

Corridor Mapping200-500 kHz pulse

rate

OR

3D LIDAR Scanning

Image Processing

o Ground Control (reference points, GPS, GNSS)

o Aero-Triangulation - (georeferencing all images a unified block and tying the block to ground control positions)

o Stereo Compilation – (3D extraction of information from the georeferenced block of imagery)

o Topographic Mapping

o Orthophotography

o Planimetric Mapping

Photogrammetric Image Processing

Contour/topographic map

Photogrammetric Image Processing

Topographic Map with Planimetric Features

Photogrammetric Image Processing

o Orthophotography

Vertical Photo Mosaic DTM/DSM (3D-view)

Photogrammetric Image Processing

Orthophotography

3D Ortho Mosaic

Photogrammetric Image Processing

UAS Survey GNSS Survey Comments

Area 1.5 km2 1.5 km2

Ground control setup &

measurement

1 ¼ hr --- Ground control not required

for all applications

Setup time 15 min 15 min (per day)

Survey time 45 min 30 ½ hr (4 days)

Tear-down time 15 min 15 min (per day)

Data processing time 4 hrs

(2.80 GHz Intel Core i7,

16 GB RAM)

--- Data can be processed

overnight

Total time 6 hr 30 min 32 hr 30 min 5x faster than GNSS

Measurement sampling Distance 3.8 cm (at 120 m flight

altitude)

15 m Minimum sampling size is 2.4

cm

Horizontal accuracy 2 cm 1 cm

Vertical accuracy 4 cm 2 cm

Land Survey vs. UAS Survey Example

Surface model generated from UAS

survey (± 300,000 measurements)

Surface model generated from GNSS

survey (±1,000 measurements)

Topographic Survey Comparison

Questions