Authors:Michael AdamsPatrick Taylor J.B. Sharma

Institute of Environmental Spatial Analysis

The Hall County National Resource Conservation Service (NRCS) has several sets of historic aerial imageryThe purpose of this project was to digitize these images such that the public can utilize them for perpetuity This project outlines the methods used in digitizing, geo-referencing, ortho-rectifying, and mosaicking a set of thirty-five images taken October 12, 1980This project was made possible by support from the Institute of Environmental Spatial Analysis at Gainesville State College and from a grant provided by the Georgia View Consortium

It is of utmost importance to preserve the vast number of vintage aerial photographs that have been taken over the last centuryThese air photos are a clear recollection of the land as it was at that moment in timeWe can use this data to increase our understanding of key features of the land, including forests, watersheds, agricultural, and urban areas The ability to use this imagery to study temporal changes of land has grown tremendously as the technology and software has advanced

approximately 394 square miles of landsplit by the Chattahoochee River and Lake Sydney Lanier. Population of193,277 according to the 2000 U.S. Census

Set of 35 Aerial images from the Hall County NRCS taken by Harris Aerial Surveys Inc.All reference Images from the Georgia Spatial Data Infrastructure (GSDI)

1. 2 meter resolution National Agriculture Imagery Program (NAIP) Hall County Mr.sid file 2006 leaf on image

2. 1999 Digital Elevation Model with a 30m resolution

Hard Copy 1 Digitizing 2 Georeferencing

3

Ortho-Rectificaton4Mosaicking5Finished

Product

Converting an analog image into a digital formatImages scanned at 300 dots per inch(dpi)Each image was 24” x 24”We outsourced this part of the project to a local commercial printing company because we needed a large format scanner to handle this size imagery

Assigning coordinates of a standard geographic reference system to a geographic feature. In the X and Y PlanesThe X, Y, and Z planes are perpendicular to one another

Representation of the X, Y, and Z planes

To correct an aerial photo for topographic relief, lens distortion, and camera tilt; to make the image true to scale as if it were a mapOrtho corrected images are corrected for changes in the Z plane

A sports stadium in downtown Toronto before and after rigorous orthorectification (Imagery courtesy of DigitalGlobe)

Image Distortions

Autosync Extension of Erdas Imagine 9.1Direct Linear Transform method:This method creates Ground Control Points between Spatial Coordinates and Image Coordinates

Corresponding GCP’s

Hall County DEM used for correction of distortions in the Z plane

Generated Cutlines

Smoothing Filter applies a blurring filter along each side of the newly generated cutlinesFeathering Filter softens the edges of the cutline by blending all of the pixels within a fixed distanceColor Balancing removes brightness variations found across the mosaicHistogram Matching creates a new histogram for all of the images to be mosaicked by matching them to one another

Image is ready for use in a GIS system for land use analyses or other research

1. Digitization of Images2. Data Management

3. Computing power

4. Root Mean Square Error

5. Mosaiclighting conditions/lens flaretransition from image to image

1. Professionally scanned2. Created standard file

structure3. Each image 350MB or >

final mosaic 4.24 GB(Terabyte server)

4. Use .5 pixel error and swipe tool to visually interpret error

5. Mosaiccolor balancing, histogram matching created cut-lines forfeathering & smoothing filters

Image Hot Spot

Seams Visible

Project Funded by a grant from The Georgia View ConsortiumThese images are now useful for scientific analysesThe Hard Copy of these images are now preserved for future generations

Questions Please …

Aronoff, Stan, 2005, Remote Sensing for GIS Managers, ESRI Press, Redlands, California, 487 p.

Marzan, G. T. and Karara, H. M. 1975. A computer program for direct linear transformation solution of the colinearity condition, and some applications of it. Proceedings of the Symposium on Close-Range Photogrammetric Systems, pp. 420-476. American Society of Photogrammetry, Falls Church.

2007, Erdas Imagine 9.1 Field Guide Volume One, Leica Geosystems Geospatial Imaging, LLC, http://gi.leica-geosystems.com/documents/pdf/FieldGuide_Vol1.pdf (March 7, 2008).

2007, Erdas Imagine 9.1 Field Guide Volume Two, Leica Geosystems Geospatial Imaging, LLC, http://gi.leica-geosystems.com/documents/pdf/FieldGuide_Vol2.pdf (March 7, 2008).

Kwon, Y.-H. (1994). KWON3D Motion Analysis Package 2.1 User's Reference Manual. Anyang, Korea: V-TEK Corporation. http://www.kwon3d.com/theory/dlt/dlt.html (March 12, 2008).