[gdal-dev] S57 questions

[ogr user]

I wonder if anyone here with a good knowledge of S57 format internals
can help me out on this issue.

OGR S57 parser seems to work quite well with most charts in NOAA ENC
data set. However, I found a feature on one of the charts that puzzles
me (to be specific, the chart is US5CA92M, the feature RCID is 1167 in
current chart edition).

This is a polygon-based feature which is defined such that, as read by
OGR, the outer polygon ring does not enclose inner rings (it is
essentially "on the side"). The first inner ring is what you would
consider the outer ring in OGR definition, if you were to visualize this
polygon. This in turn causes all sorts of issues (in particular in any
code that assumes the entire polygon to be enclosed in the outer ring).

So, my question is - is it that S57 standard allows for multiple outer
rings for polygons and so this is not handled in OGR because OGRPolygon
is defined that way? Is it an error in S57 data, something that chart
makers did? Or is it, perhaps, something in DDF encoding that is not
read correctly by the iso8211 module?

Any help on this would be appreciated.

--Mike