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Optimize Your Aerial Imagery With True Orthos

Posted by Cathy Wolniewicz on Aug 21, 2019 10:04:54 AM

Orthophotos are the standard when it comes to aerial imagery, but information is obscured, i.e. by building lean. Skyline’s software creates "true orthos" revealing a more accurate and complete picture of features in the image. 

Standard Orthophoto Limitations

Orthophotos, or vertically photographed aerial images, are by far the most widely used imagery datasets and are available from several suppliers. Used on their own or combined with other geospatial datasets, they are of great value for adding context to other mapping and giving a realistic view of the “lie of the land”. Orthophotos have also entered the public's consciousness thanks to Google Earth.

However, there are downsides to these everyday aerial images. Firstly, the scale of work involved in gathering and processing the data is immense, therefore updating it is expensive and slow; for some areas the best available imagery might be 2-3 years old.

Another problem may arise due to the nature of vertical imagery capture. The ground immediately below the survey aircraft will be captured as a precise vertical view but moving outwards, the angle of view is affected so that tall buildings, mountains and trees appear to lean away from the centre. This can be especially frustrating in urban areas where the lean of a tall building can obscure the streets below. For example:

Aerial Oblique Ortho Image

Here, the lean on the six-story building has blotted out much of the surrounding ground area. It just so happens that this building is in Romsey, Hampshire, which we recently modelled using PhotoMesh loaded with data captured via the fast, cost effective XCAM methodology.

Rectifying Obscured Data 

Using the same software, we then made our own orthophotos. These orthophotos from PhotoMesh are "true orthophotos". In the rectification process, the 3D model is used to move objects to their correct 2D position, so for example, roofs are moved on top of the ground footprint of the building so the walls are not visible, but the surrounding ground area is:

True Ortho Made from PhotoMesh

Now, with the six-story building accurately rectified, the orthophoto shows much more relevant detail.


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Identifying Anomalies 

Here is another example demonstrating the value of PhotoMesh true orthos.  Looking again at our orthophotos from the Romsey project, we noticed the nave roof of Romsey Abbey has a surprising bulge on its south side:

The Value of True Ortho Built by PhotoMesh

The bulge measures as just over 0.5m at the maximum.  I am told by the Abbey authorities that the bulge has been there a long time (several hundred years!) and the Abbey is not in danger of falling.

So, OK; whilst this anomaly is not of immediate concern to the custodians of Romsey Abbey, can you imagine the power and value such orthophotos bring to modern-day Developers, Planners, Insurance Risk Assessors etc.?  Particularly now that XCAM data capture plus PhotoMesh processing makes orthophotos/3D models affordable and cost effectively updateable?

Learn More about Skyline's Authoring Tools; PhotoMesh and TerraBuilder. 

this article was posted on behalf of SkylineGlobe UK. If you are in the UK and are interested in learning more about how to purchase Skyline Products, visit their webpage.  

Topics: PhotoMesh, True Orthos