6.2 Georeferencing
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Transcript 6.2 Georeferencing
Laura Johnson
Wen Andrews
NSF DUE-1205110;
0903270
GeoTEd Partners
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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
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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
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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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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
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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
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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
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Questions?
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0903270