Northing/easting shift information at BSB charts
|Reported by:||vadp||Owned by:||warmerdam|
Some commercially available BSB charts have local, non-WGS84, datum assigned to. Hence registration reference points (REF<n>/) at their headers are assigned to that datum. Processing these charts with the current GDAL tools results in chart features shifted north-south and/or east-west against their real position.
It appears that such charts have northing/easting information encoded at their headers to bring their coordinates to WGS84 datum. It's encoded by a line like this:
where <northing> and <easting> are longitude and latitude shifts in *seconds* (floating point numbers) to bring that local datum to WGS84.
In essence, these shifts are to be added to REFs coordinates to produce a correct data. This idea was proved by a bash script I wrote for the purpose to create a VRT file with correct coordinates referencing to an original KAP file wich contains BSB data (see attachment).