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would not return accurate results. A study of sediment levels in drains or canals,
for example, could not be developed using the methods outlined here because of
the difficulty in getting a large enough sample to train the image key.
The method outlined can be used against small area polygons, so can be applied to
land use types across most of the country, with the exception of full urban areas
and remote mountain areas (where the small land divisions are not found). It
should be noted that the target areas described refer to peri-urban data. This is
because fully urban areas are covered by large scale 1:1000 mapping and spectral
analysis would not improve on the available data (outside of highly specialized
heat radiation studies etc., which are not the intended use for this method). The
method could also be used by someone seeking to trace patterns in land use over
recent decades. This study would be confined to RGB photography as a
comparative analysis of the properties of the pixel counts by colour band are a
requirement for the process. Once the proposed key is calibrated for the particular
run of photography, the algorithm could be set to run for a specified region of
interest across the period when this type of photography was available.
This differs from previous studies looking at automatic aerial photography in two
ways. Firstly, the focus is specific to Irish ordnance survey data and concentrates
on making use on the codes and known values that can be extracted from this.
Secondly, the study uses small area polygons to target the spectral analysis of the
imagery to relatively small sample areas. This is to reduce the difficulty posed by
variations in pixel values found in large samples. In this the process is relatively
unique as it takes the small area polygons as a guide and cuts the matching areas
from the raster aerial imagery. This allows for automatic decisions to be made
regarding the level of standard deviation present in the sample. In many ways this
simplifies the process of image interpretation because most of the difficult image
control work is completed and the software can then focus on variations specific
to the ground cover being studied. While this has limitations on the extension of
the work to other (general small scale) datasets it does outline a method for
automating the search of imagery. Over the course of the last two years of this
Masters study I have learned about how users can interrogate and manipulate data
in large databases.
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