CS 128/ES Lecture 10a1 Raster Data Sources: Paper maps & Aerial photographs

CS 128/ES Lecture 10a2 Georgian’s First Law of GIS Try to use somebody else’s data before you even think of generating your own.

CS 128/ES Lecture 10a3 Data sources: overview Raster sources: Paper maps Aerial photographs Satellite images Vector sources: Digitized maps Surveying Global positioning system

CS 128/ES Lecture 10a4 Paper maps

CS 128/ES Lecture 10a5 Using paper maps in a GIS 1. Scan to image file (usually JPEG or GIF) 2. Georeference the image to the GIS coordinate system 3. (If desired) digitize the features in the image to generate 1+ vector layers

CS 128/ES Lecture 10a6 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 Lecture 10a7 Affine transformations Translation Rotation Scaling Skew

CS 128/ES Lecture 10a8 Georeferencing in ArcMap - 1

CS 128/ES Lecture 10a9 Georeferencing in ArcMap - 2

CS 128/ES Lecture 10a10 Georeferencing in ArcMap - 3

CS 128/ES Lecture 10a11 Georeferencing in ArcMap - 4

CS 128/ES Lecture 10a12 Georeferencing in ArcMap - 5

CS 128/ES Lecture 10a13 Georeferencing in ArcMap – 5b

CS 128/ES Lecture 10a14 Georeferencing in ArcMap - 6

CS 128/ES Lecture 10a15 Georeferencing in ArcMap - 7

CS 128/ES Lecture 10a16 Georeferencing in ArcMap - 8

CS 128/ES Lecture 10a17 Georeferencing in ArcMap - 9

CS 128/ES Lecture 10a18 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 Lecture 10a19 “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 Lecture 10a20 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 Lecture 10a21 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 Lecture 10a22 Scale Determine from: Plane altitude RF = 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 Lecture 10a23 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 Lecture 10a24 Planimetric view Perfectly vertical (orthogonal) perspective All features in correct horizontal positions Impossible unless at infinite height

CS 128/ES Lecture 10a25 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 Lecture 10a26 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 Lecture 10a27 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 Lecture 10a28 Stereoscopic photo pairs Image from Avery. Interpretation of Aerial Photographs.

CS 128/ES Lecture 10a29 Stereoscopes need pair of overlapping photos different principle points results in parallax used to create topographic contours

CS 128/ES Lecture 10a30 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 Lecture 10a31 Rectification process 1.Scan aerial photograph at high resolution 2.Locate ground control points on scanned image: ≥3 for affine transformation ≥5 for rubbersheeting 3.Combine with digital elevation model (DEM) to correct relief displacement 4.Rectify to a ground coordinate system

CS 128/ES Lecture 10a32 Relief distortion Objects at different distances form the lens will be distorted

CS 128/ES Lecture 10a33 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.

CS 128/ES Lecture 10a34 Result: digital orthophotograph USGS: DOQQs NYS GIS Clearinghouse Or, new aerial photos & image rectification ($$$) Wind Cave N P Vegetation Survey?Sure (tax $$) No!!!CS 128/ES 228 Course Project?