ESRI ArcMap Georeferencing

ESRI ArcMap Coordinate Transformations - Ground to Grid

• Universal World File - esri_cad.wld
  • "The universal world file is for defining a transformation for all CAD drawings in a workspace. The esri_cad.wld file will apply to all CAD drawings in that folder that do not already have a world file designated. If one exists for a specific CAD drawing, it will override the esri_cad.wld file." (see ArcGIS Desktop 9.3 Help - World files)
• Problems
  • Raster Images Not Supported. ESRI world files (.wld) and universal world files (esri_cad.wld) do NOT support Raster images. Must manually transform the images. Since aerial imagery is usually flown at the beginning of a project and is rarely updated, this manual conversion will only have to be done once. Not like GIS layers such as parcel owners which needs to be updated throughout the project design. It appears you have to make your own world file to transform raster datasets from ground to grid. See ArcGIS Desktop 9.3 Help - World files for raster datasets
  • Georeferencing video sample
  • Georeferencing a raster dataset

ArcMap - Georeference Raster Image using a World File

• Step 0: Datasets
  • Grid Coordinate Files:
    • shapefile of streets surrounding Jean NV - sclsubset.zip.
    • Final output of the aerial photo transformed from ground to grid coordinates - TopoImageSPCS.zip
    • Color aerial photo for GIS central repository: S0721713.zip
  • Ground Coordinate Files:
    • Black and White aerial photo (tiff image .tif with world file .tfw) of Jean Nevada in ground coordinates TopoImage-014.zip
    • AutoCAD DWGs: TopoDWGs.zip
• Step 1: Using ESRI's ArcMap application, add shapefile based on grid coordinates. Using Stateplane Coordinate System (SPCS). Notice the x,y coordinates in the status bar, e.g. 694450.694, 26652372.143 feet, this gives a tip your using a Grid coordinate system instead of a local/ground coordinate system. Also, in the ArcMap table of contents, right click the Layers Data Frame and select properties. Under the Coordinate System tab, will see we are indeed using a Grid Coordinate System, namely NAD_1983_StatePlane_Nevada_East
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• Step 2: add a new dataframe. Using Add Data, open the raster image which is in ground coordinates. Notice the x,y coordinates in the status bar, e.g. 5000.000 5000.000
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• Step 3: within ArcMap table of contents, drag the local coordinate raster image into the first data frame which has the shapefile in stateplane coordinates
• Step 4: turn on the Georeferencing Toolbar
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• Step 5: under the Georeferencing Menu, click Fit to Display. This is really just an optional step.
• Step 6: click the View Link Button. New window opens, then click load. Navigate to the world file (.wld)
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• Step 7: if Auto Adjust is turned on, then the image will be rectified.
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• Step 8: to save the changes click Georeferencing -> Rectify.... If you choose the TIFF option, will create a GeoTIFF image that is in SPCS. Will also create an auxiliary file (.aux or .aux.xml) and a pyramid file (.rrd).
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  • Info on auxiliary files (.aux) see ArcGIS Desktop 9.3 Help - About auxiliary files
  • Info on pyramid files (.rrd) see ArcGIS Desktop 9.3 Help - About reduced resolution dataset files
  • "Note: CAD transformations can never have more than two control points in the Link Table." (see ArcGIS Desktop 9.3 Help - Transforming CAD datasets)