NSF DUE-1205110; 0903270

Using outside data: CAD, digitizing, and georeferencing

Laura JohnsonWen Andrews

NSF DUE-1205110; 0903270

GeoTEd Partners

NSF DUE-1205110; 0903270

Module OutlineDigitizingGeoreferencingUsing CAD Data

NSF DUE-1205110; 0903270

Digitizing data

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What is Digitizing?The process of making paper (analog) maps

digitalGeoreferencing

Registered to the correct part of the map Projection/Coordinate system defined

Defining attributesPopulating attribute fields

NSF DUE-1205110; 0903270

Digitizing methodsCreate new Feature Class (point, line, or

polygon) to store new digital featuresUse 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

Georeferencing datasets

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What is georeferencing?Sometimes called “rubber sheeting”Rectifying or registering an image to the

correct geographic locationCAD dataScanned mapAerial photos

Can be a time-consuming processAuto Georeferencing available for datasets that

are very similarMatch points on the scanned picture to known

points on the map

NSF DUE-1205110; 0903270

Georeferencing in ArcGISStart with a map with the data you will match

“to”Add the raster dataset you want to

georeferenceAssign 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

NSF DUE-1205110; 0903270

Georeferencing in ArcGISHow many control points?

Best to spread out to the corners of the imageCheck 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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Using CAD Data in ArcGIS

NSF DUE-1205110; 0903270

What is CAD Data?Vector filesCommon applications

SurveyingCivil EngineeringArchitectureLandscape architecture

File typesDWGDGN

NSF DUE-1205110; 0903270

Importing CAD DatasetsCan be added directly from ArcCatalog or the

Add Data button Typically lots of features in one dataset

Geometry, text, and symbolsDefinition Queries can help to filter data

Usually need to be projectedCan also be imported to a Geodatabase

NSF DUE-1205110; 0903270

Questions?