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2 Stepping through the Algorithm<br />
This thesis introduces a method for analyzing aerial imagery that can be translated<br />
into a procedure and run automatically. The operation is specific to two types of<br />
data<br />
• Digital vector files from the ordnance survey.<br />
• Controlled aerial photography stored as GeoTiff files.<br />
Both of these data sources are projected using ITM projection and are referenced<br />
during the study. The premise of the study is that it is possible to automatically<br />
capture additional information about area polygons from aerial photography using<br />
previously captured vector polygons as a guide. It is an attempt to fill in the blanks<br />
in terms of polygon attributes not included in the photogrammetry which led to the<br />
vector data. The focus is not primarily to obtain an accurate list of all polygons<br />
from the sample data but instead to identify a verifiable method for automatically<br />
doing so. As the focus is on the identification of methods, the process that is<br />
outlined can be extended to apply to searches for specific spectral qualities –in<br />
other words someone searching for a particular crop type might employ the<br />
algorithm here, but add a target set of data specific to their work. In short what<br />
follows is an attempt to take the two data sets mentioned above (photography and<br />
vector data), combining them and returning a new set of information derived from<br />
both. The process does not merge the data sources but uses the vector data (a large<br />
portion of which was derived from the photography) as a reference to cut<br />
segments from the imagery and treat these segments as smaller manageable pixel<br />
collections for analysis. This process is helped by the fact that the content of many<br />
of these polygons is known and has been coded to the vector data.<br />
What was completed in the sampling part of the thesis was an attempt to identify<br />
specific spectral qualities that can be applied to these known polygons, and then<br />
used to reference the unknown areas. This had a reasonable level of success with<br />
some polygon types making a more useful reference than others. A description of<br />
these can be found in the sampling section of this study. Automated aerial image<br />
analysis generally focuses on attempting to determine the values of the imagery<br />
18
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