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How it works?

1. Orthoimages

1.1. Ortho preprocessing level

An orthoimage is the result of complex geometric processing to obtain a high level of accuracy.

The ortho product level corrects residual parallax errors due to relief. This is performed using ground control points (GCPs) and a digital elevation model (DEM).

The orthorectification process eliminates the distorsions due to relief and performs transformations required to project an image in a specified map projection (Lambert conformal, UTM, polar stereographic, etc.). The image thus obtained is GIS-, GPS- and map-compatible.

1.2. Location accuracy

The location accuracy depends directly on DEM and GCP quality. Spot Image generates orthoimages using its unique Reference3D geographic reference database, which ensures a location accuracy of 10 metres rms whatever the terrain relief and viewing angle in the original imagery.

1.3. Applications

Ortho products are especially appropriate in areas with relief. This highly sophisticated level of preprocessing is suitable for compiling and updating geographic databases and maps, where maximum accuracy is required. It also lets you overlay or mosaic an image with other orthoimages, even those acquired from other sensors.

2. Reference3D geographic reference system

The geographic reference system used to orthorectify your data is derived from stereopair images acquired by the High Resolution Stereoscopic instrument (HRS) on SPOT 5 ( http://www.spotimage.fr/web/732-spot-3d.php ).

Spot Image started to build up the Reference3D database in 2002 when SPOT 5 (equipped with the HRS sensor) was launched. Processing large blocks of HRS data allows to guarantees an absolute accuracy and a shared registration of between 2 orthoimages that are of higher quality than a pixel, whenever iswhatever the acquisition date.

Reference3D comprises 3 layers of information:

·       DTED level 2 DEM

·       HRS orthoimage with horizontal accuracy of 10 metres rms

·       Quality metadata

Over 100 million sq.km. of imagery are available for orthorectification. It is being regularly updated and will cover most of the globe by end 2008. If our geocoded database doesn’t yet cover your area of interest, contact our sales team at salesonline@spotimage.fr to discuss an alternative solution.

3. SPOTOrtho Online service

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