6.2 Georeferencing

Report
Laura Johnson
Wen Andrews
NSF DUE-1205110;
0903270
GeoTEd Partners
NSF DUE-1205110;
0903270
Module Outline
 Digitizing
 Georeferencing
 Using CAD Data
NSF DUE-1205110;
0903270
NSF DUE-1205110;
0903270
What is Digitizing?
 The process of making paper (analog) maps digital
 Georeferencing


Registered to the correct part of the map
Projection/Coordinate system defined
 Defining attributes
 Populating attribute fields
NSF DUE-1205110;
0903270
Digitizing methods
 Create new Feature Class (point, line, or polygon) to
store new digital features
 Use a digitizing tablet and puck to digitally “trace” paper
map

“Antiquated method
 Scan a paper map


Register (georeference) new image
Create points, lines, or polygons using scanned image and
remostely sensed imagery for reference
NSF DUE-1205110;
0903270
NSF DUE-1205110;
0903270
What is georeferencing?
 Sometimes called “rubber sheeting”
 Rectifying or registering an image to the correct geographic
location
 CAD data
 Scanned map
 Aerial photos
 Can be a time-consuming process
 Auto Georeferencing available for datasets that are very
similar
 Match points on the scanned picture to known points on
the map
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0903270
Georeferencing in ArcGIS
 Start with a map with the data you will match “to”
 Add the raster dataset you want to georeference
 Assign control points
 Matching a point on the target dataset to the base data
already on the map
 Continue until the datasets are lined up as well as
possible
Source: ArcGIS 10.1 help
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Georeferencing in ArcGIS
 How many control points?
 Best to spread out to the corners of the image
 Check the links table


RMSE, lower is better
Can add and delete points while checking the table
 Transformation


Permanent warping of the target dataset
Not always necessary but can help reshape the data
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Transformation types
Source: ArcGIS 10.1 help
NSF DUE-1205110;
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NSF DUE-1205110;
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What is CAD Data?
 Vector files
 Common applications
 Surveying
 Civil Engineering
 Architecture
 Landscape architecture
 File types
 DWG
 DGN
NSF DUE-1205110;
0903270
Importing CAD Datasets
 Can be added directly from ArcCatalog or the Add
Data button
 Typically lots of features in one dataset
 Geometry, text, and symbols
 Definition Queries can help to filter data
 Usually need to be projected
 Can also be imported to a Geodatabase
NSF DUE-1205110;
0903270
Questions?
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0903270

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