MORE INFORMATION ABOUT WP1/WP2 - HR land-cover mapping

 

•  Rectification: Gathering of Ground Control Points (GCPs) for Dublin was laborious. Two sources of GCPs were used:

    * points taken during a differential-GPS survey combining a "pseudo-permanent" station and a rover (13-16 November 2007);

    * points selected on the 1m-resolution orthophotos from the web server of the Ordnance Survey of Ireland.

The destination cartographic reference system is the Irish National Grid. A systematic shift on the GPS measurements (+2.12m; -2.58m) was applied to reduce the difference between the transformation based on GPS-GCPs and the one based on OSI-GCPs (see figure on the right).

Finally, 23 coherent points were used, 9 from the translated GPS-GCPs and 14 from the OSI-GCPs to determine a second order polynomial transformation. The global RMSE computed by cross-validation is 1.21m ( 1.13 m for X and 0.46 m for Y).

 


Error vectors showing the difference between transformations based on GPS-GCPs and OSI-GCPs
(A = before and B = after applying a systematic shift on the GPS points; filled triangles = OSI-GCPs,
unfilled triangles = GPS-GCPs)

 

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MORE INFORMATION ABOUT WP1/WP2 - HR land-cover mapping

 

  

Pre-classification: The ISODATA classifier was applied in a 4 steps-procedure on the 3 first components of the PCA of the 4 pan-sharpened bands (see figure on the left).

In each step of the procedure an a posteriori interpretation of the sub-classes in non-ambiguous and ambiguous categories determines the following classification step, which is applied to the ambiguous sub-classes only.

By a map-overlay process, 44 final non-ambiguous sub-classes were obtained.

The signatures of the 44 sub-classes were then extracted from the 4 pan-sharpened bands at the 0.61m resolution to train a Maximum Likelihood classifier, producing more homogenous and spatially better structured sub-classes than the ISODATA classifier.

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Last modification date = 7-06-2009