Photogrammetry, Photography, Oblique, Vertical, Melbourne, Hobart, Adelaide, Brisbane, Australia

Over the years "aerial surveyors" have been using aerial photography to produce topographic maps and plans. In recent years, the emphasis for this type of output has swung to 'soft-copy' or digital output.

In the digital form, both vector (lines) and raster (images) can be used together to produce orthophotos. The orthophoto is a scale corrected photograph and can be georeferenced and produced with topographic map features such as
contours, grids, scale, bars etc.

The accuracy of an orthophoto depends largely on the scale of the photography, resolution of the scanned image (photograph) and accuracy of both the photocontrol and digital terrain model.

As an indication, we would expect that using a photograph with a scale of 1:5000 and scanned at a resolution of 800 dpi, with suitable photocontrol and digital terrain model would obtain an orthophoto accurate to ± 0.2 metres on the ground. The orthophoto has one main advantage over the normal map or plan in that it is much easier to interpret and recognise the features.