Automated aerial image analysis using ordnance survey vector data

Abstract

This study sets out an algorithm for the automatic analysis of controlled (flattened) aerial photography using ordnance survey vector data. It uses the vector to clip the aerial image into a set of small area polygons which are then analyzed for the spectral properties and classified according to the result. The study tests sections of aerial photography from a sample area in County Galway for specific spectral properties. This was to identify the type of ground cover and was achieved using an image key of spectral properties which was developed during the study. This is called training the image key. A testing section shows that it is possible to derive information about the land use type from these areas based on the range of values returned from a pixel count of spectral properties within a small area polygon.

The study uses several open source software frameworks to complete the experiment, most notably the MATLAB based Mirone application, but can be extended to any software capable of handling irregular polygons in a projection system. The body of the study is set out in three chapters, the first detailing the process, the second detailing the sampling for unique values and the third details the testing which took place. Chapters 3 and 4 are sub divided into sections describing the research on specific land use types and their spectral signatures.

Chopping an aerial image into a mosaic of (relatively) homogenous values, e.g. pasture, forestry, marsh etc., increases the accuracy of automated analysis. This is the first time that a spectral analysis has been attempted using ordnance survey Ireland small area polygons to clip the image. It is of interest to researchers, planners, developers etc., looking to simplify and automate this type of search over a large region.

Note: Contact brian.sexton@osi.ie for a set of sample files for training the image key.