[Gdal-dev] Arc Binary Coverages

[Craig Miller]

Matt,

A coverage contains one data layer, along with different types of topology.
These would all continue to be accessible if the Workspace was considered
the datasource.  They would all have the same name, but a different type
attribute.  Perhaps we would have to append something to the coverage name
to make it clear since OGIS (and as a result OGR) doesn't support as many
types as the Arc Coverage model, but rather maps some of the types to a
simple feature.  A name such as <layer> <type> would work.  For example,
"Streams (ARC)".  This appears to be more intuitive, informative, unique,
and closer to the true name of the coverage that always using "ARC".

The workspace is also where the attribute database is stored and it contains
information such as Librarian data and Image Catalog data.  Right now, there
is no way to add support for Librarian to the driver (which is actually
where I started looking at this).

I was thinking that regions will continue to be supported with a name such
as <layername> - <region> <type>.  For example "Streams -
Lake_Wenatchee_Basin (region)"

I'm still pretty confident that the two data models map perfectly onto each
other with exception to the fact that OGIS/OGR have smaller set of supported
layer types.  Naming conventions seems like an easy way to work around this
and still preserve the simple features nature of the OGR library.

--Craig


-----Original Message-----
From: Matthew Perry [mailto:perrygeo at gmail.com] 
Sent: Monday, November 14, 2005 2:52 PM
To: Craig Miller
Cc: Gdal-Dev
Subject: Re: [Gdal-dev] Arc Binary Coverages

Craig,

  There are good reasons to treat the coverage, rather than the workspace,
as the dataset. The biggest reason is that a coverage contains multiple data
layers (tics,lines, centroids, polygons or points, etc). In addition
ArcInfo's regions data model allows you to store many spatially-related
layers within a single coverage.

If the workspace were the dataset and the coverage were the layer, there
would be no way to get at the region layers (or tics, or any of the other
supporting spatial data) within the coverage.

I happen to work with regions occasionally so I'm very thankful for the way
OGR handles ArcInfo Coverages! ;-)

matt

On 11/14/05, Craig Miller <craig.miller at spatialminds.com> wrote:
>
>
>
> Is there a reason why the Arc Binary Coverage driver uses the Coverage 
> directory instead of the Workspace that is traditionally used in Arc/Info?
>
>
>
> E.g. I would have expected to pass a directory to the workspace like 
> /data/county and receive back a list of coverages in that workspace such
as:
>
>
>
> Lakes - Type:Polygon
>
> Lakes - Type:Point (Polygon Labels)
>
> Lakes - Type:Linestring (Polygon boundary with line topology built)
>
> Roads - Type:Linestring
>
> Etc.
>
>
>
> Instead it asks for a path to the coverage /data/county/lakes and 
> returns layers named things such as ARC.
>
>
>
>
>
>
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>


--
Matt Perry
perrygeo at gmail.com
http://www.perrygeo.net