2019 NYSAPLS Conf> Fundamentals of Photogrammetry for Land Surveyors George Southard GSKS Associates LLC Introduction 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” data processing using the science of Photogrammetry Definitions: 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. Key Technologies and Terms • 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 History A brief history of Photogrammetry Origins of Remote Sensing Remote sensing began with aerial photography First photographs taken in 1839 A brief history of Photogrammetry Paris by Nadar, circa 1858 1858 Gasper Felix Tournachon "Nadar" takes photograph of village of Petit Bicetre in France from a balloon. 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 Foundational Principles Photogrammetric Fundamentals First Assumption: the photo image is a flat planar surface Photogrammetric Fundamentals 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) 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 Aerial Photography -Stereo pair •Over lap about 60% Precisely controlled image capture….. •Over lap about 60% Types of Photogrametry Photogrammetric Types 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+ Close Range (terrestrial) Photogrammetry Close Range (terrestrial) Photogrammetry Aerial Photogrammetry Space Photogrammetry ❖ Extraterrestrial pictures taken from space- based cameras Photogrametric Imagery Introduction Types of Images • Panchromatic, Black & White, Grayscale • Color - Red Green Blue (RGB) • Multispectral (RGB + Infrared) • Hyperspectral Panchromatic Image Sensitive to light in the 400-680nm range 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 – Aerial Photo ❖Seldom used for mapping Low oblique (no horizon) High Oblique – Aerial Photo • Horizon line in the photo • Typically used for 3D city modeling Aerial images are not maps! Characteristic of a Map vs a 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 Image Acquisition for photogrammetric mapping Image Acquisition Precisely controlled image capture….. Precisely controlled image capture….. Image Acquisition • Photos taken in parallel flight strips Image Acquisition • Each successive photograph overlap previous photo 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 Types of Stereo Model control layout Aero-Triangulation - (georeferencing all images for a unified block of ground control positions and tie points) Photogrammetric Instruments Direct Optical Projection Stereo plotters • 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 Softcopy (digital) Stereo plotters Digital Softcopy Stereoplotter 1990s - Present 3D Aerial Film Cameras Wild C2 - 1927 Wild RC5 - 1944 Wild RC30 & Zeiss TOP15 – 1980s Imaging Cameras for Manned Aircraft RGB and IR Large Format ≥200 MP Medium Format RGB or IR 60 - 100 MP Small Format RGB or IR 10 – 20 MP Imaging Cameras for Unmanned 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 Does camera choice effect accuracy? 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 Sensor Size vs. image noise Camera Sensor Dimensions Rows x Columns (pixels) Pixel Area (μm2) (mm) 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. Image Noise Noise from Cannon S100 images Significant Noise Poor Conformance Image Noise Noise from NEX-5R Images Low Noise High Conformance Focal length calibration 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. Other Issues…. • 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 options o Requires special lenses (which are expensive or not available for many consumer cameras.) 3D LIDAR Scanning • Airborne LIDAR: Manned Aircraft Wide Area Mapping 500-800 kHz pulse rate OR Corridor Mapping 200-500 kHz pulse rate Image Processing Photogrammetric 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 Land Survey vs. UAS Survey Example UAS Survey GNSS Survey Comments Area 1.5 km2 1.5 km2 Ground control setup & 1 ¼ hr --- Ground control not required measurement 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 --- Data can be processed (2.80 GHz Intel Core i7, overnight 16 GB RAM) Total time 6 hr 30 min 32 hr 30 min 5x faster than GNSS Measurement sampling Distance 3.8 cm (at 120 m flight 15 m Minimum sampling size is 2.4 altitude) cm Horizontal accuracy 2 cm 1 cm Vertical accuracy 4 cm 2 cm Topographic Survey Comparison Surface model generated from UAS survey (± 300,000 measurements) Surface model generated from GNSS survey (±1,000 measurements) Questions.