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Ortho, or rectified photography, has the geometric
accuracy of a map but contains the immense detail
of a photograph. Orthophotos are produced at prices
often comparable to, or less than, standard topographic
mapping, due to reduction in labor component. The
popularity of digital orthophotography is growing
fast with the advent of more powerful computers and
software.
The applications for digital orthos are widespread.
One of the most common uses is a backdrop for GIS
applications. Contours can also be overlaid on the
digital ortho if desired. If planimetric features
are desired, the level of detail captured is left
to the client. Some features that are less important
may be left out of the planimetric capture, but are
still visible on the digital image. Another advantage
over conventional orthophotos is the ability to alter
the scale of the image and the ability to plot at
different scales. The accuracies obtained are approximately
the same as conventional mapping using stereoplotter,
however the overall accuracy is determined by the
scan resolution and the accuracy of the DEM or DTM.
For example, a horizontal or vertical measurement
of less than one meter can’t be obtained from
a digital image scanned with a two-meter ground pixel
resolution.
In conclusion, digital orthophotography has become
a very useful tool that has many advantages over conventional
mapping and conventional orthophotography. The main
advantage is the ability to manipulate the output
and viewing scales and the ability to plot hardcopy
prints without the need for expensive photo lab equipment.
Also, the introduction of higher-powered computers
with huge storage capabilities has placed this technology
in the hands of smaller companies and government agencies
with smaller budgets.
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