{ "culture": "en-US", "name": "Imagery_1966", "guid": "", "catalogPath": "", "snippet": "Black and white imagery for the City of Harrisonburg taken on 11/23/1966.", "description": "

The orthoimagery in this image service was taken on 11/23/1966 over Harrisonburg, VA. Data was supplied from James Madison University. Dr. Glen Gustafson's ISAT Applied GIS Lab created this mosaic for the City of Harrisonburg from scanned prints. The dataset's coordinate system is WGS 1984 Web Mercator (Auxiliary Sphere). A cache was built using the ArcGIS Online/Bing Maps/Google Maps tiling scheme containing 11 levels ranging from 1:288,895 to 1:282.<\/SPAN><\/P>

Metadata from JMU students<\/SPAN><\/P>

1) April 30, 2004 - Rebecca Farmer<\/SPAN><\/P>

Orthocorrection of the City of Harrisonburg 1966<\/SPAN><\/P>

I was involved with the Harrisonburg City Aerial Mapping Project. The project entailed the georeferencing and the orthocorrecting of historical aerial photography for the City of Harrisonburg, 1966, in ERDAS Imagine. Once the orthocorrection was completed, a mosaic was combined of each photograph into a single photomap, one for each year of aerial photography.<\/SPAN><\/P>

This lab entailed orthocorrecting aerial photographs of the City of Harrisonburg for the year 1966. The input materials included three scanned aerial photographs, exposures 223, 224, and 225, of the city taken on November 23, 1966, a digital elevation model with 30 meter pixels, and a digital raster graphic of the area.<\/SPAN><\/P>

My first task was to properly scan the three air photos. I then imported the images into ERDAS. My next step was to orthocorrect each of the three air photos. To orthocorrect the image in ERDAS, I selected camera as the geometric model. The camera correction model entailed importing the DEM, selecting the focal length of the camera, digitizing the fiducials and selecting the projection. For exposure 223 through 225, the image indicated the focal length was 208.99mm. After the camera model properties were complete, I could begin georeferencing my image. For exposure 223, I used nine points to georeference with a total RMSE error of 7.8788. I also used nine points to georeference for exposure 224 which gave me a final RMSE of 5.0610 for that exposure. For exposure 225, I used seven points to georeference, and received an RMSE of 5.7482. The images were then each resampled, and three orthophotos were produced.<\/SPAN><\/P>

For quality assurance of my work, I checked the information on the image information screen to see if my images had the correct projection. I found that all images had the correct projection, UTM Zone 17, Clarke 1866, and NAD27; and all images were unsigned 8-bit data with pyramid layers present and a pixel size of one meter. I then used the swipe tool in ERDAS to compare my images with the Harrisonburg Reference DRG; each image lined up well with the DRG\u2019s features.<\/SPAN><\/P>

The last step required Sarah Coleman and I to mosaic the six images together. Using ERDAS\u2019s Data Prep, we cropped borders by 30% and feathered our images. Our mosaic had the correct projection information.<\/SPAN><\/P>

2) April 17, 2004 - Sarah Coleman<\/SPAN><\/P>

Orthocorrection of the City of Harrisonburg<\/SPAN><\/P>

I was involved with the Harrisonburg City Aerial Mapping Project. The project entails georeferencing and orthocorrecting historical aerial photography for the City of Harrisonburg in ERDAS Imagine. Once the orthocorrection is completed, a mosaic will combine each photograph into a single photomap, one for each year of aerial photography. Each mosaic will then be set into a \"Map Composition\" to produce a formal photomap, which can be used as a backdrop for any GIS operations at the City.<\/SPAN><\/P>

This lab entailed orthocorrecting aerial photographs of the City of Harrisonburg. The input materials included three scanned aerial photographs, exposures 12, 13, and 14, of the city taken on November 23, 1966, a digital elevation model with 30 meter pixels, and a digital raster graphic of the area.<\/SPAN><\/P>

To orthocorrect the image in ERDAS, I selected camera as the geometric model. The camera correction model entailed importing the DEM, selecting the focal length of the camera, digitizing the fiducials and selecting the projection. For exposure 12, the image indicated the focal length was 208.99mm. The error of the digitized fiducials was 3.8. For exposure 13, the error was 6.5. Finally for exposure 14, it was 7.5. After the camera model properties were complete, I georeferenced my image. Only three GCP's are needed; however, I used eleven for exposure 12. The RMS error was 8.0 pixels. Nine points were selected for images 13 and 14. The RMS error for exposure 13 was 7.0. Exposure 14 had an error of 6.4. The images were then each resampled, and three orthophotos were produced.<\/SPAN><\/P>

The quality of the orthocorrected images is less than the scanned image. Data is lost when any image is orthocorrected. The images information screen reveals the correct projection (UTM Zone 17, Clarke 1866, and NAD27), unsigned 8-bit data with pyramid layers present and a pixel size of one meter. The histograms are fairly normally distributed. The images were swiped with the DRG. Each image lined up extremely well with the map's features.<\/SPAN><\/P>

Lastly, Rebecca Farmer and I mosaicked our images together. Using ERDAS's Data Prep, we cropped borders off and feathered our images. The final product had a fairly normally distributed histogram, the correct projection information, and it lined up well with the Digital Raster Graphic's features.<\/SPAN><\/P><\/DIV><\/DIV><\/DIV>", "summary": "Black and white imagery for the City of Harrisonburg taken on 11/23/1966.", "title": "Imagery_1966", "tags": [ "JMU", "City of Harrisonburg" ], "type": "Image Service", "typeKeywords": [ "Data", "Service", "Image Service", "ArcGIS Server" ], "thumbnail": "thumbnail/thumbnail.png", "url": "https://gis.harrisonburgva.gov/image", "minScale": 288895.277144, "maxScale": 282.124294, "spatialReference": "WGS_1984_Web_Mercator_Auxiliary_Sphere", "accessInformation": "JMU, City of Harrisonburg", "licenseInfo": "

Every reasonable effort has been made to assure the accuracy of this dataset and associated maps. The City of Harrisonburg assumes no liability arising from use of these datasets or maps created using these datasets. THE DATASETS ARE PROVIDED WITHOUT WARRANTY OF ANY KIND, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Any errors or omissions should be reported to the GIS Administrator of the City of Harrisonburg, Department of Information Technology.<\/SPAN><\/P><\/DIV><\/DIV>" }