[gdal-dev] Shapefile OGR question/concern

[Nikos Alexandris]

On Wed, 2008-03-12 at 15:48 -0400, Christiaan Janssen wrote:
> Hi all,
> I'm having an issue with the Shapefile driver within OGR. When
> exporting data from an OGRDataset to a shapefile I'm required to add
> an additional "closing point" (ie repeat the first point at the end)
> for the resultant shapefile to be correctly recognized in other
> viewers (I realize the shapefile spec calls for this). The problem is
> that other formats do not require this closing point (eg KML) and
> adding the additional point results in additional point being written
> to the outputted file, not what I would believe to be correct. It
> would seem then that depending on my output I would have to reformat
> my data, seemling defeating the purpose of having an interfaced method
> library like OGR. Am I incorrect in my assumption and/or is there
> another intended way to do this correctly. 

I am sure that you will get "better" replies to this from the Experts.
But I'll give it a shot since I had a similar issue.

The "closing point" has to be there in case you are dealing with closed
polygons (areas). Without it (in other words without first and last
point identical) polygons are not really "closed" and therefore
topologically not "clean".

Non-topological formats like ESRI Shapefiles can live with that and
therefore cleaning is highly recommended.

.

Some weeks ago I was trying to import KML's polygons into GRASS the data
appeared broken (open polygons, missing lines (?) and even a centroid
falling outside an area (?))


>  
> Christiaan

Cheers,

Nikos
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