[gdal-dev] Missing features after copying layers from Shapefiles to SQLite

[Nik Sands]

You are correct - I did misunderstand.  Thanks for further explaining the multiple geometries to me.  :-)

So it looks like the best option for me is to make a copy of each source layer which may contain both single and multi variants (eg, point and multipoint features) and make the new SQLite layer use the multi variant (eg, multipoint) and perhaps I will need to convert every single variant feature (eg, point) to the multi variant (eg, multipoint).

I've written some code to try to do this but its rather long and clumsy (and doesn't actually work as yet).  I can't help but think there's got to be a better way and that I'm doing it all wrong.  Is there any precedent or preferred way that this should be done?

I think that perhaps my understanding of the API is a bit lacking in this area.


On 4 Mar 2014, at 8:31 pm, Jukka Rahkonen <jukka.rahkonen at mmmtike.fi> wrote:

> Nik Sands <nixanz <at> nixanz.com> writes:
> 
>> 
>> Thanks Chaitanya,
>> It's finally dawned on me that this is what the following is about in the
> OGR SQLite format web page:
>> 
>> 
>> Tables with multiple geometries
>> Starting with OGR 1.10, tables that have multiple geometry columns
> registered in geometry_columns can be used by OGR. For such tables, there
> are as many OGR layers exposed as there are geometry columns. They are named
> "table_name(geometry_column_name)".Note: this support is limited to
> read-only operations.
>> 
>> Ah... so multiple geometries are NOT avaiable in this format for writable.
>> 
>> Your idea of forcing all geometries to multies is a good idea.  I'll have
> to figure out the most efficient way to do this when converting an entire
> layer at a time, but it's likely to be much better than the way I'm
> currently doing it and would result in the same number of layers as the
> original, which is preferable, especially when the user wants to manage
> drawing styles for layers.
> 
>> Thanks for your idea.  I'm very grateful.
> 
> Hi,
> 
> You perhaps understood wrong what was said about multiple geometries.
> Multipolygon is a single geometry. Multiple geometry columns means a
> situation when one feature has many geometries, for example a polygon
> geometry, simplified polygon geometry and point geometry presenting the
> centroid of the polygon. All in one row in a same table but in three
> geometry columns.
> 
> I think also that a standard solution in to create multilinesting and
> multipolygon tables into Spatialite and write also simple geometries as
> multivariants. Principally same for multipoints, but at least in data I
> usually use such do not exist. But you know your data and can decide. It is
> also possible to create a Spatialite table with a generic "GEOMETRY"
> geometry type. Such table accepts all kind of geometries but it may me
> tricky to use data in applications.
> 
> -Jukka Rahkonen-
> 
>> 
>> Cheers,
>> Nik.
> 
> 
> 
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