Photogrammetry Course Quiz - Module 6

Course Review Modules

• Module 1: Introduction to Photogrammetry & Platforms
• Module 2: Models, Orientation & Stereoscopic Vision
• Module 3: Planimetric Capture & 3D Digitizing
• Module 4: Terrestrial Photogrammetry & 3D Models
• Module 5: Flight Planning
• Module 6: Photo Acquisition, Processing and ABGPS
• Module 7: Orthophotos
• Module 8: Data Visualization and Mapping
• Module 9: Image Interpretation and Analysis
• Module 10: Digital Elevation Model(s)
• Module 11: Photogrammetry Applications, Limitations & Review
• Module 12: RPAS Applications - Guest lecture Dec 3

Key Concepts Learned

• Platforms: Manned Aircraft (large areas), RPAS (Drones) (small areas), Terrestrial (close range). Satellite images are not covered in this course.
• Sensors/Frames: Large/medium format cameras (e.g., UltraCam Eagle, Leica DMC-4, Leica CityMapper) and close-range cameras (e.g., Phase One P5, DJI The Zenmuse P1, DJI ZENMUSE L2, Sony RX1R ii). Sensor field of view vs instantaneous field of view—sensor FOV is the angle corresponding to each side of the frame, and instantaneous FOV is the angle corresponding to a single pixel. Each sensor/camera frame is usually rectangular.
• Sensors/Frames - Nadir and Oblique Images: Nadir is a vertical/nadir image where the camera's optical axis is pointing straight down. Oblique image is where the camera's optical axis is at an angle.
• Sensors/Frames - Waves and Surfaces Interaction: Transmission, reflection, refraction, diffraction, absorption, and scattering related to how light waves interact with surfaces. A spectral reflectance curve is included, showing reflectance percentages (%) against wavelength (micrometers), with examples of dry soil, healthy vegetation and clear water.
• Passive vs Active Sensors: Passive sensors (covered in course) don't emit energy (e.g., optical/infrared). Active sensors (not covered) emit energy (e.g., LiDAR/RADAR).
• Geometric Distortions: Lens distortion, terrain/relief displacement, camera optical axis/tip and tilt, atmosphere refraction, and earth curvature. Correcting for these requires calibration or models. Image motion is another distortion.
• Resolutions: Spectral (ability to detect different spectral bands: black and white (panchromatic), RGB, multispectral/RGB/NIR, hyperspectral), radiometric (ability to detect small differences in energy), and spatial (ability to detect small ground details, from 2cm and up).
• Stereo Pairs, Overlap and Geometry: Showing side lap, front lap, and overlap of aerial photos and drones (60/30 and 80/80, etc.).
• Photo Scale: The relation between flying height above ground (AGL), focal length of the camera, and ground pixel size. Includes calculations for average scale. Ground pixel size can vary based on topography, meaning it varies across an image.
• Photo Frame and Scale: including terms like principal point, fiducial mark, fiducial center, nadir point, principal point from the photo, etc.
• Data types & Presentations (Data Pyramids & Tiles): Primarily for raster data, designed to manage very large datasets in a way that helps with displaying different resolutions in a hierarchical way.
• Compression Effect: Lossy (compressed beyond recovery), Lossless (compressed but recoverable).
• Mathematical Models: Includes the collinearity model and the coplanarity model for relationships between object space and image space. Rotation around photo x, y, and z axes are also included.
• Relief Displacement: Importance of knowing object height to correct distances from relief distance.
• Parallax: Apparent displacement of an object as seen from two different points (different points on the principal point).
• Interior, relative, and absolute orientations: Interior orientation (relationship between sensor and image coordinate systems, x,y of PP, focal length), relative orientation (aligns one photo to another), and absolute orientation (oriente photo to a ground coordinate system). Common methods, like RTK, PPK, and PPP, are included.
• Stereoscopic Vision: Overview of basic concepts including interocular distance, stereo pairs, misalignment and aligned stereo models and von Gruber points. Includes pocket stereoscopes and anaglyphs, and examples of software workstations used.
• Photogrammetry and Mapping Applications: Large and medium scale compilation of different types of maps (roads, neighborhoods, trees etc.) are included here.
• Cameras, Properties: Includes fixed focal length, fixed distance for photogrammetry, high-quality lens, large sensor, and precise tolerances.
• Controls for Terrestrial Photogrammetry: Control points, scale bars, etc.
• Base-to-Distance Ratio: Ratio between the base and distance relevant to stereo vision (1:4 to 1:15).
• BIM & Digital Twin: Overview of BIM (collaborative design & build process that visualizes physical and functional aspects of a building) and digital twin (a virtual replica of physical entities).
• Flight Planning: Design of flight path & height, speed, covering area of interest, meeting specifications, and cost-effectiveness.
• Optimum Flying Height: Factors including map/orthophoto scale, contour factor and interval, GSD, pixel size, image resolution, topography, air traffic restrictions, and accuracy.
• Pixel Size - Orthorectification Factor: Importance of the resampling process in orthorectification that increases the pixel size by a factor of 1.2.
• OFH - Contour Factor and Interval: Values typically ranging from 1800 to 2400 (dimensionless) and used to determine the flying height.
• OFH - GSD: Finding the Ground Sampling Distance, relationship to flying height and spatial resolution, and the meaning of a given GSD. Also, relative accuracy, relationship and formula.
• OFH - Image Resolution: What's the smallest object that needs to be clearly visible? Is a single pixel sufficient? How many pixels are required to positively detect an object?
• Seasonal Considerations: Springtime (few leaves) is ideal for maximum land exposure, while summer (in full bloom) provides minimum land exposure. Other weather factors like temperature, precipitation and wind.
• Sun Angle Considerations: Low sun angle creates shadows. High sun angle can lead to overexposure. Important range of sun angles.
• Execution: Where Can I Fly?: Regulations for operation within different airspace types.
• Execution: Safety: Safety equipment and procedures (pad, anemometer, safety cones, etc.) for RPAS operations, and that flying drones can be dangerous.
• Metric Cameras: Designed for photogrammetry, fixed lens focused on infinity, no zoom, high-quality lens, little or no distortion.
• Non-Metric Cameras: Not designed for photogrammetry, use zoom lenses, variable focus, unknown interior orientation parameters (focal length and principal point), lens distortion, and measurement errors.
• Camera Settings: Aperture, shutter speed, and ISO, all related to exposure and brightness.
• Motion Blur: Understanding motion blur, how it's related to flying speed, flying height and shutter speed, and what is the GSD.
• Processing: Differential GPS vs PPP: Differential GPS: needs a base station within 25-50 km of the rover. PPP does not need one. Both are accurate, but PPP is becoming more common as it matures.
• Overview: Standard orthos use DEMs/DTMs which only corrects ground elevations, true orthos correct elevated features like buildings and trees, DSM is available from LiDAR technology.
• GCP Processing (AT/BBA): GCPs (Ground Control Points) are used for processing and their importance and properties regarding sizes and types.
• Orthorectification: Transformation from radial view to an orthogonal view, new pixel positions (re-projection), which considers control points, polynomial rectification, and differential rectification.
• Quality Control: Checks before delivery including geographic extent, projection and coordinate system, format, naming convention, tiling, and metadata.
• Image Enhancement: Covers histogram, linear stretch, percentage stretch, histogram matching, spatial filtering, noise reduction, deblurring, Wiener and wavelet filters, and reflectance calibration.
• Band Combinations: Useful relationships between reflectance and features like leaf pigments, leaf structure, water content, leaf biochemicals, senescence, and soil. Wavelength ranges are covered.
• Thermal Imaging and Forest Fire: Unique aspects of thermal bands, emitted heat, and example (Town of Lytton).
• Raster 2d, 2.5d, and 3d: Covers overview of data types.
• Tiles and Pyramids: Efficient way to manage and visualize large raster datasets based on hierarchical tiling schemes for resolutions, size and data.
• Manual/Visual vs Digital Interpretation: Comparison of methods; manual methods require no special equipment, but digital methods require specialized software and computers.
• Visual Interpretation: How visual elements like tone, shape, size, etc. can make interpretation more difficult.
• Computer Based Analysis & Interpretation: Computer-based methods like pixel based and object based classification (including supervised vs unsupervised).
• Digital Terrain Models (DTMs): Representations of the Earth's surface, giving elevation data, types (DSM, DEM). Including different modeling methods (grid, TIN).
• Interpolation Techniques: The methods used to estimate unknown points based on sample data points.
• DTM/DEM Data Sources: Various methods for creating DTMs/DEMs such as land surveys, existing contours, photogrammetry, satellite imagery (including stereo), radar (active-sensor), and LiDAR.
• Summary: All the concepts studied in the previous sections are summarized in a concise manner. Includes important applications, limitations and overall review.

Test your knowledge on the concepts covered in Module 6 of the photogrammetry course. This quiz addresses topics such as sensor fields of view, digital elevation models, and various types of image compression. Challenge yourself to recall key definitions and applications within photogrammetry!