Post on 16-Jan-2016
GIS 1
GIS Lecture 6Digitizing
GIS 2
Outline
•Digitizing Overview•Digitizing Sources•GIS Features•Creating and Editing Shapefiles in ArcView•Spatial Adjustments•Conclusion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 3
Digitizing Overview
GIS 4
Why Digitize?
•New maps•Map features are wrong•Missing features
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 5
Heads Down Digitizing
• Digitizing table or tablet
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 6
Heads Up Digitizing
• Mouse on a screen• Digitizes paper maps, aerial photos, or
other images
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 7
Digitizing Sources
•Orthophotos•GPS•Paper Maps•Scanning•Raster to Vector Conversion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 8
Orthophotography•Digital imagery in which distortion from the camera angle and topography have been removed, thus equalizing the distances represented on the image
•Can be used to measure true distances• http://gis.esri.com/library/userconf/proc95/to150/p124.html
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 9
DOQQs
•Digital Ortho Quarter Quadrangles•Produced by the U.S. Geological Survey (USGS)
•Grayscale or color-infrared (CIR) images•1-meter ground resolution; •Cover an area measuring 3.75- minutes longitude by 3.75-minutes latitude, approximately 5 miles on each side
•Referenced to the North American Datum of 1983 (NAD83) and cast on the Universal Transverse Mercator (UTM) projection.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 10
Image Resolutions
The amount of detail found in one pixel of the image. •image with one meter resolution means that each pixel in the image represents one square meter on the ground.
30 meters 30 meters 10 meters 10 meters 5 meters 5 meters
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 11
Image Resolutions (Continued)
2 meters 2 meters 1 meter 1 meter
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GIS 12
Resources
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GIS 13
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 14
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 15
Resources (Continued)
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GIS 16
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 17
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 18
Resources (Continued)
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 19
Resources (Continued)
Google Maps
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 20
Resources (Continued)
Google Earth
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GPS
•Department of Defense built the global positioning system (GPS) in the 1970s
•Network of up to 24 satellites in earth orbit
•Opened it up to civilian use in the 1980s – free of charge
•GPS uses triangulation from signals from the satellites
•Base stations are fixed receivers that help GPS signals get accuracy within 1 to 5 meters
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GPS (Continued)
•Easy to input GPS data into GIS
•GPS is most valuable when there are no base maps sufficient to guide drawing new features
GIS 23
National Spatial Reference System
•National network of control points (small brass disks with identifiers and marks) placed on permanent structures such as concrete posts
•National Geodetic Survey (NGS) establishes the known points
•Surveyors take measurements (angles and distances) from known locations to accurately locate points and boundaries
•By the early 1990s, GPS became the dominant method for establishing control points
•Some cities maintain their own points
GIS 24
National Spatial Reference System
City of Pittsburgh control point benchmark
GIS 25
Paper Maps
Historic Maps•http://www.usgsquads.com/svcs_historic_maps.htm#Historic•http://digital.library.pitt.edu/maps/-Historic maps of Pittsburgh and Allegheny County from 1872-1939
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 26
Scanning Paper Documents
•Scanned maps and images become vectors
•Special software needed
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GIS 27
Raster to Vector Conversion
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GIS 28
Raster to Vector Conversion
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 29
GIS Features
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Points•Nodes-Single points-Alone or at endpoints of lines
00
node
1
2 3
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GIS 31
Points• Vertices- Control the shape of lines
00
nodevertex
2 3
1
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GIS 32
Points• Tics- control points used to register the map to the
geographic space
00
nodevertextic
2 3
1
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 33
Lines
•Connected Nodes and Vertices•Single or multipart features
00
node
1 2
line
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GIS 34
LinesFNODE_ TNODE_ LENGTH STREET_ STREET_ID FNAME LEFTADD1LEFTADD2RGTADD1 RGTADD2
180 129 595.106800 201 51635798 Kirkpatrick 605 699 600 698
From Node
To Node
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 35
Line Features with VerticesFNODE_ TNODE_ LENGTH STREET_ STREET_ID FNAME LEFTADD1LEFTADD2RGTADD1 RGTADD2
180 129 595.106800 201 51635798 Kirkpatrick 605 699 600 698
Vertex
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 36
TIGER LINE Files
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GIS 37
TIGER Street Centerlines
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GIS 38
TIGER Street Centerlines
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 39
Polygons
•Closed lines• Single polygons or multipart features
(e.g. Hawaiian islands can be multiplepolygons as one feature)
00
node
1 2
polygon
4 3
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 40
New Shapefiles
GIS 41
Creating New Shapefiles
•Create new point, line or polygon shapefile in ArcCatalog
•Add Spatial Reference Information (optional)•Add New Shapefile in ArcMap•Edit shapefile to add features and attributes •Stop editing •Save edits as part of new shapefile
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 42
New Shapefiles - ArcCatalog• Cannot create shapefiles in ArcMap
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 43
Add Shapefile in ArcMap
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GIS 44
Heads Up Digitizing•Add base layers if necessary
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GIS 45
Heads Up Digitizing•Add Editor Toolbar
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 46
Heads Up Digitizing•Start Editing
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GIS 47
Heads Up Digitizing•Begin Digitizing•Click Sketch Tool
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 48
Heads Up Digitizing•Start Drawing Points
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Heads Up Digitizing•Stop Editing•Save Edits
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Heads Up Digitizing•Add attribute information
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Editing Shapefiles
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Lines and Polygons•Advanced editing tools-Editing Vertices-Snapping Functions-Multipart Features
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 53
Editor Toolbar
Editor Toolbar Sections
- Editor drop-down
- Sketch tool
- Tasks
- Target
- Attribute Inspector
- Sketch properties
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 54
Sketch Construction Tools
Sketch tool:• Use to create point features and to digitize the
vertices of line or polygon features. Intersection tool:
• Creates vertex at place where two segments intersect
Arc tool:• Creates a segment that is parametric (true)
curve. Only has two vertices as endpoints Midpoint tool:
• Define the location of the next vertex by on two points - the vertex is place at the midpoint of the line between these points
End Point Arc tool:• creates true curve by defining the start and end
points of the curve, then define a radius
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 55
Sketch Construction Tools
Tangent Curve tool • Creates segments that are tangent
Distance-Distance tool• Creates a point or vertex at the intersections of two
distances from two other points
Direction-Distance tool• Like distance-distance tool except second point
uses a direction from a known point to define a bearing line
Trace tool:• Create segments that follow along existing
segments
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 56
Tasks• Most features are
created and modified through sketches
• Tasks define what you do with a sketch
• Create features
• Modify features
• Reshape features
• Other edit tasks
• Custom tasks
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 57
Target Layer•Target layer determines to which layer a new feature will belong
•Can edit multiple layers in an edit session
•Subtypes are also listed*
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 58
Spatial Adjustments
GIS 59
Spatial Adjustments
•Transform•Rubbersheet•Edgematch
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GIS 60
Transforms•Convert data from one coordinate system to another.
•Converts data from digitizer or scanner units to real world coordinates.
•Shifts data within a coordinate system, such as converting feet to meters.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 61
Rubbersheeting•Geometric distortions commonly occur in source maps.
•They may be introduced by imperfect registration in map compilation, lack of geodetic control in source data, or a variety of other causes.
•Rubbersheeting corrects flaws through the geometric adjustment of coordinates.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 62
Edgematching•The edgematching process
aligns features along the edge of one layer to features of an adjoining layer.
•The layer with the less accurate features is adjusted, while the adjoining layer is used as the control.
•Attribute transfer is typically used to copy attributes from a less accurate layer to a more accurate one.
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 63
Spatial Adjustment Example•Hamburg Hall Building Drawn in CAD
•Spatially Adjusted to Aerial Photo
Copyright– Kristen S. Kurland, Carnegie Mellon University
GIS 64
Summary
•Digitizing Overview•Digitizing Sources•GIS Features•Creating and Editing Shapefiles in ArcView•Spatial Adjustments•Conclusion
•More to Explore-Tutorial 6 (Introduction to Digitizing)-On-line Help (Advanced Topics)
Copyright– Kristen S. Kurland, Carnegie Mellon University