1 / 34

Raster Data Sources: Paper maps & Aerial photographs

Raster Data Sources: Paper maps & Aerial photographs. Georgian’s First Law of GIS. Try to use somebody else’s data before you even think of generating your own. Data sources: overview. Raster sources: Paper maps Aerial photographs Satellite images Vector sources: Digitized maps

winter
Télécharger la présentation

Raster Data Sources: Paper maps & Aerial photographs

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Raster Data Sources:Paper maps & Aerial photographs CS 128/ES 228 - Lecture 10a

  2. Georgian’s First Law of GIS Try to use somebody else’s data before you even think of generating your own. CS 128/ES 228 - Lecture 10a

  3. Data sources: overview Raster sources: • Paper maps • Aerial photographs • Satellite images Vector sources: • Digitized maps • Surveying • Global positioning system CS 128/ES 228 - Lecture 10a

  4. Paper maps CS 128/ES 228 - Lecture 10a

  5. Using paper maps in a GIS • Scan to image file (usually JPEG or GIF) • Georeference the image to the GIS coordinate system • (If desired) digitize the features in the image to generate 1+ vector layers CS 128/ES 228 - Lecture 10a

  6. Georeferencing raster images • Spatial coordinates may be absent or purely map coordinates (i.e. inches from one corner) • Control points: point features visible on both the image and the map • Linear or nonlinear transformations • “Rubber sheeting” CS 128/ES 228 - Lecture 10a

  7. Affine transformations • Translation • Rotation • Scaling • Skew CS 128/ES 228 - Lecture 10a

  8. Georeferencing in ArcMap - 1 CS 128/ES 228 - Lecture 10a

  9. Georeferencing in ArcMap - 2 CS 128/ES 228 - Lecture 10a

  10. Georeferencing in ArcMap - 3 CS 128/ES 228 - Lecture 10a

  11. Georeferencing in ArcMap - 4 CS 128/ES 228 - Lecture 10a

  12. Georeferencing in ArcMap - 5 CS 128/ES 228 - Lecture 10a

  13. Georeferencing in ArcMap – 5b CS 128/ES 228 - Lecture 10a

  14. Georeferencing in ArcMap - 6 CS 128/ES 228 - Lecture 10a

  15. Georeferencing in ArcMap - 7 CS 128/ES 228 - Lecture 10a

  16. Georeferencing in ArcMap - 8 CS 128/ES 228 - Lecture 10a

  17. Georeferencing in ArcMap - 9 CS 128/ES 228 - Lecture 10a

  18. Digitizing raster layers Digitizing table • high resolution (0.001”) • either point or stream mode • paper shrinkage/ expansion • data in “table coordinates” – need to convert to map coordinates CS 128/ES 228 - Lecture 10a

  19. “Heads up” digitizing Tracing on computer monitor: • many scanned (raster) file formats supported • poorer resolution, but uses less specialized equipment • best for adding small # features or updating a file • uses coordinate system of image or base map CS 128/ES 228 - Lecture 10a

  20. Aerial photographs • HUGE amount of detail • VAST number of photographs are available, often for free • Digitizing and photo-interpretation can produce vector layers and attribute data CS 128/ES 228 - Lecture 10a

  21. Photogrammetry • Originally, the science (or art?) of interpreting aerial photographs • Stress on quantitative measurements • Now includes analysis of digital images from many sources Image from Avery. Interpretation of Aerial Photographs. CS 128/ES 228 - Lecture 10a

  22. Scale Determine from: • Plane altitudeRF = lens focal length altitude of plane • Known ground features Top image from Avery. Interpretation of Aerial Photographs. Bottom images from Ben Meadows catalog (L), Olean NW DOQQ ® CS 128/ES 228 - Lecture 10a

  23. Perspective • Vertical:- orthogonal perspective- planimetric map data • Oblique: - high oblique (includes horizon) - low oblique (no horizon) Image from Avery. Interpretation of Aerial Photographs. CS 128/ES 228 - Lecture 10a

  24. Planimetric view • Perfectly vertical (orthogonal) perspective • All features in correct horizontal positions • Impossible unless at infinite height CS 128/ES 228 - Lecture 10a

  25. The principle point • Point directly under camera lens (‘nadir’) • Elevated objects lean away from PP • Depressed objects lean toward PP • Causes horizontal image displacement Images from Avery. Interpretation of Aerial Photographs. CS 128/ES 228 - Lecture 10a

  26. Vertical relief -> displacement • Transmission line is straight - why does the line appear straight in one photo and jagged in the second? • In left photo, line is ~ on nadir; in right photo, the line is far from nadir Image from Avery. Interpretation of Aerial Photographs. CS 128/ES 228 - Lecture 10a

  27. Image displacement: • Source of error in horizontal locations, but • Permits estimation of feature elevations stereoscopic parallax Image from Avery. Interpretation of Aerial Photographs. CS 128/ES 228 - Lecture 10a

  28. Stereoscopic photo pairs Image from Avery. Interpretation of Aerial Photographs. CS 128/ES 228 - Lecture 10a

  29. Stereoscopes • need pair of overlapping photos • different principle points results in parallax • used to create topographic contours CS 128/ES 228 - Lecture 10a

  30. Rectification of aerial photographs Rectification: process of geometric correction that turns an aerial photograph into a planimetric (map-like) image Problems: • Earth curvature • lens distortion • camera tilt • terrain relief CS 128/ES 228 - Lecture 10a

  31. Rectification process • Scan aerial photograph at high resolution • Locate ground control points on scanned image: ≥3 for affine transformation ≥5 for rubbersheeting • Combine with digital elevation model (DEM) to correct relief displacement • Rectify to a ground coordinate system CS 128/ES 228 - Lecture 10a

  32. Relief distortion Objects at different distances form the lens will be distorted CS 128/ES 228 - Lecture 10a

  33. Urban areas: building tilt In urban areas, tall buildings seem to lean toward the principal point of the photograph Corrected by building a digital terrain model (DTM) of each building Permits virtual reality “flyovers” Thorpe, A. Digital orthophotography in New York City. www.sanborn.com/Pdfs/Article_DOI_Thorpe.pdf CS 128/ES 228 - Lecture 10a

  34. Result: digital orthophotograph • USGS: DOQQs • NYS GIS Clearinghouse • Or, new aerial photos & image rectification ($$$) Wind Cave N P Vegetation Survey? Sure (tax $$) CS 128/ES 228 Course Project? No!!! CS 128/ES 228 - Lecture 10a

More Related