What is an orthophoto?

The digital imaging department at Qasco produces spatially referenced thermal and photographic imagery utilising the method of orthorectification. Orthorectification uses complex mathematical algorithms to remove distortions caused by variations in elevation, lens distortion, and camera tilt within a photograph.

Unlike a standard aerial photograph in which straight lines are bent and displaced due to variations in scale, an orthophoto can be used to measure true distances as it posesses map-like qualities. These include having a uniform scale, being geo-referenced, and fitting corresponding planimetric data.

Who uses orthophotos?

Orthorectified imagery is commonly used by local, state, and the Commonwealth governments, developers, mining corporations, and other land related industries. They are used to assist in future planning, displays and presentations, to show the history of an area, and they can be placed into use as-is or used as a basis for a GIS database.

How are orthophotos made?

To produce digital orthophotography, the original aerial film is first scanned using a radiometrically and geometrically precise digital aerial film scanner. The images are aerotriangulated using Leica Geosystems ORIMA Orientation Management software and the data is processed using proprietary production systems such as BAE SOCET SET and Leica Photogrammetry Suite. Additional image processing may be performed using popular imaging software programs.

The use of this latest technology creates a superior product compared to earlier processes, but is heavily reliant on the base ground control and elevation model. If either is substandard, the overall quality of the ortho is affected, which is why Qasco offers a full range of spatial services to ensure a high-quality deliverable at every stage of the process.

All digital products can be delivered in specified CAD or GIS formats to meet customer requirements, including AutoCAD, MicroStation, and ArcGIS.

What orthophoto products are available?

Our digital technicians can supply customers with:

> Rubber sheet mosiacs (low accuracy) - These products are loosely fitted to ground control points and are akin to draping a flexible substrate over an elevation model.
> Orthorectified mosiacs (high accuracy) - These products are fully geo-referenced and accurate to the same resolution standards as maps.
> Digital data - Depending on the needs of the customer, we can supply compiled data in the form of either Digital Elevation Models (DEM) or Digital Terrain Models (DTM).

> Hard copy plots - These plots differ from photogrammetric plots because they show detail through the image. The plots can be supplied with geo-referenced vector overlays.
> Historical orthophotos - We can produce orthos from any set of stereoscopic photography for historical and heritage purposes.

Other products that the digital imaging department specialise in include: