Browsing by Author "Dr. Hugh A. Devine, Chair"

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    Digital Vegetation Delineation on Scanned Orthorectified Aerial Photography of Petersburg National Battlefield
    (2000-11-27) Millinor, William A.; Dr. Hugh A. Devine, Chair; Dr. George R Hess, Committee Member, Member; Dr. Heather M. Cheshire, Committee Member, Member
    I developed a new methodology to produce an orthorectified mosaic and a vegetation database of Petersburg National Battlefield using mostly digital methods. Both the mosaic and the database meet National Map Accuracy Standards and proved considerably faster than traditional aerial photograph interpretation methods. I classified vegetation polygons to the formation level using the Nature Conservancy's National Vegetation Classification System. Urban areas were classified using Mitchell's Classification Scheme for Urban Forest Mapping with Small-Scale Aerial Photographs. This method reduced the production time by 2/3, compared to traditional methods. It also reduced the chance of user error because re-tracing of the linework is not required. My method started with scanning 75 aerial color IR photos, provided by Petersburg National Battlefield, at 600 dpi. Erdas Imagine was used to rectify the images using United States Geological Service (USGS) Digital Elevation Models (DEM) and black and white USGS Digital Orthophoto Quarter Quadrangles (DOQQ) as reference. The images were then mosaiced to create a seamless color infrared orthorectified basemap of the park. The vegetation polygons were drawn onscreen using ArcMap from Environmental Systems Research Institute, Inc. (ESRI) with the color, orthorectified mosaic as a background image. Stereo pairs of the aerial photos were referenced as needed for clarification of the vegetation. I used a minimum mapping unit (mmu) of 0.2 hectares, which exceeds guidelines defined by the United States Geological Survey — National Park Service Vegetation Mapping Program. This methodology is easily learned quickly and has already been applied to several other studies. The production of an orthorectified mosaic, created during the process, from the aerial photographs greatly increases the value of the photographs at little additional cost to the user. The orthorectified basemap can then be used as a backdrop for existing data layers or it can be used to create new GIS data layers. I used a minimum mapping unit (mmu) of 0.2 hectare, which exceeds guidelines defined by the United States Geological Survey-National Park Service Vegetation Mapping Program. Traditionally, vegetation polygons are delineated on acetate for each photograph. The linework on the acetates is then transferred to a basemap using a zoom transfer scope or other transfer instrument. The linework is traced again to digitize it for use in a GIS program. This process is time consuming, and the linework is drawn three times. The redundant tracing increases the chance of user error. My new methodology requires that polygons be delineated only once. I wanted to avoid using the zoom transfer scope and to avoid the redundant linework. A total of 228 polygons were delineated over 20 separate vegetation and land cover classes with an overall thematic accuracy of 87.42% and a Kappa of .8545. Positional accuracy was very good with a RMSE of 1.62 meters in the x direction and 2.81 meters in the y direction. The Kappa and RMSE values compare favorably with accuracies obtained using traditional vegetation mapping methods.
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    Image Integration and On-Screen Digitizing Method of Geographic Information System Update and Maintenance Applied to the Hofmann Forest
    (2002-04-22) Moore, Jennifer Anne; Dr. Hugh A. Devine, Chair; Dr. Heather M. Cheshire, Member; Dr. E. Carlyle Franklin, Member
    The Hofmann Forest is a self-sustaining forest that provides the North Carolina State University College of Natural Resources with support for research, education, and extension service. The management of the Hofmann Forest requires data concerning historical records, complete and current resource inventory, and the ability to model future forest conditions. A geographic information system (GIS) database was created for the Hofmann Forest in 1992 to facilitate achievement of these data objectives. The database was not maintained or used regularly. Ongoing forestry research and silvicultural activities are constantly changing the resource conditions on the forest. This research examined a practical and accurate method for maintaining currency in the GIS database. Digital imagery was integrated into the original GIS database, and silvicultural records were used to update the existing data layers. Digital orthophotography, in the form of USGS Digital Orthophoto Quarter-Quads (DOQQs), was the primary source of imagery, but where the imagery was unavailable or contained insufficient spatial detail, unrectified aerial photographs were scanned, registered, and substituted. For the vegetation data layer of the GIS, spatial and attribute updates were completed and evaluated for silvicultural operations covering over three thousand acres. Some updates involved only changes in attributes. Spatial updates were completed with the digital orthophotography or digital aerial photographs; of these, some updates involved fairly simple spatial editing and others involved more complex spatial editing. The updates required the digital aerial photographs were all spatially complex edits. Acreage estimates accompanied the silvicultural records. GIS-derived area measurements were compared with those on the silvicultural records. There was not a significant difference between the two measures of area, however some discrepancies were present. A series of comparison tests were designed and performed to identify the potential elements of the area discrepancies. Spatial complexity of the editing procedure, different sources of digital imagery, and size of updated vegetation polygons were all examined. Degree of spatial complexity in the updates did not significantly contribute to area discrepancies. There was no significant difference in area discrepancies when either the DOQQs or digital aerial photographs were used. Size of the updated vegetation polygons was significantly negatively correlated with the discrepancies, showing that small absolute differences in area in small polygons result in large relative discrepancy values. Differentially corrected global positioning system (GPS) data were used to assess the horizontal positional accuracy of the GIS data layers. Following National Map Accuracy Standard (NMAS) guidelines, a sample of 25 'well-defined' locations were collected using a Trimble GPS Pathfinder ProXR receiver with real-time differential correction capabilities. These same locations were identified on the Roads layer of the GIS database, the DOQQs, and the digital aerial photography. Root mean-square error (RMSE) was calculated for each of the different data layers, using the GPS data as reference locations. Only the DOQQ-derived points met the NMAS Class 2 horizontal positional accuracy standard. RMSE for the aerial photography and Roads layer were greater than the limiting RMSE for the NMSE Class 3 standard. Based on these results, it can be concluded that DOQQs possess greater horizontal accuracy than the digital aerial photography and are the preferred imagery source for the on-screen digitizing. Should greater resolution be required for a database update, orthorectification of the digital aerial photography could be used to correct horizontal positional errors. Recently, software packages have become available to orthorectify aerial photographs effectively and affordably.The presence of extraneous features in the vegetation layer of the GIS database almost certainly contributes to the area discrepancies. Features such as windrows, fire ponds, and logging decks are included in vegetation polygon area but not silvicultural record area estimates. Future database improvements should consider subtracting these features (and their associated areas) from the vegetation layer and creating separate database layers for each type of feature. A methodology report was developed to accompany the GIS database as a reference for future updating. Continuous maintenance of the Hofmann Forest GIS database is necessary to provide timely information for on-site forest managers and research activities, and to preserve an account of forest conditions that may be useful in present and future management decisions. On-screen digitizing with integrated digital imagery proved to be a feasible method for updating and maintaining the Hofmann Forest GIS database.