raster data sources: paper maps & aerial photographs
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
CS 128/ES 228 - Lecture 10a 1
Raster Data Sources:Paper maps &
Aerial photographs
CS 128/ES 228 - Lecture 10a 2
Georgian’s First Law of GISTry to use
somebody else’s data before you
even think of generating your
own.
CS 128/ES 228 - Lecture 10a 3
Data sources: overviewRaster sources: Paper maps Aerial photographs Satellite images
Vector sources: Digitized maps Surveying Global positioning system
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Paper maps
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Using paper maps in a GIS1. 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 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”
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Affine transformations Translation
Rotation
Scaling
Skew
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Georeferencing in ArcMap - 1
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Georeferencing in ArcMap - 2
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Georeferencing in ArcMap - 3
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Georeferencing in ArcMap - 4
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Georeferencing in ArcMap - 5
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Georeferencing in ArcMap – 5b
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Georeferencing in ArcMap - 6
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Georeferencing in ArcMap - 7
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Georeferencing in ArcMap - 8
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Georeferencing in ArcMap - 9
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Digitizing raster layersDigitizing table high resolution (0.001”) either point or stream
mode paper shrinkage/
expansion data in “table
coordinates” – need to convert to map coordinates
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“Heads up” digitizingTracing 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
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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
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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.
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ScaleDetermine 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 ®
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Perspective Vertical:
- orthogonal perspective- planimetric map data
Oblique: - high oblique
(includes horizon) - low oblique (no horizon)
Image from Avery. Interpretation of Aerial Photographs.
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Planimetric view Perfectly vertical
(orthogonal) perspective
All features in correct horizontal positions
Impossible unless at infinite height
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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.
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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.
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Image displacement: Source of error
in horizontal locations, but
Permits estimation of feature elevations
stereoscopic
parallaxImage from Avery. Interpretation of Aerial Photographs.
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Stereoscopic photo pairs
Image from Avery. Interpretation of Aerial Photographs.
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Stereoscopes need pair of
overlapping photos
different principle points results in parallax
used to create topographic contours
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Rectification of aerial photographsRectification: process of geometric correction
that turns an aerial photograph into a planimetric (map-like) image
Problems: Earth curvature lens distortion camera tilt terrain relief
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Rectification process1. 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
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Relief distortionObjects at different distances form
the lens will be distorted
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Urban areas: building tiltIn 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
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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?