EVOLUTION-MANAGER

Edit File: drv_fme.html

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<title>FMEObjects Gateway</title>
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<h1>FMEObjects Gateway</h1>

Feature sources supported by FMEObjects are supported for reading by OGR
if the FMEObjects gateway is configured, and if a licensed copy of
FMEObjects is installed and accessible.<p>

To using the FMEObjects based readers the data source name passed should
be the name of the FME reader to use, a colon and then the actual data
source name (i.e. the filename).  For instance, "NTF:F:\DATA\NTF\2144.NTF"
would indicate the NTF reader should be used to read the file

There are a number of special cases:<p>

<ul>
<li> A data source ending in .fdd will be assumed to be an "FME Datasource
   Definition" file which will contain the reader name, the data source name,
   and then a set of name/value pairs of lines for the macros suitable to pass
   to the createReader() call.  <p>

<li> A datasource named PROMPT will result in prompting the user for
   information using the regular FME dialogs.   This only works on Windows.<p>

<li> A datasource named "PROMPT:filename" will result in prompting, and then
   having the resulting definition saved to the indicate files in .fdd format.
   The .fdd extension will be forced on the filename.   This only works on
   Windows.
</ul>

Each FME feature type will be treated as a layer through OGR, named by the
feature type.  With some limitations FME coordinate systems are supported.
All FME geometry types should be properly supported.  FME graphical attributes
(color, line width, etc) are not converted into OGR Feature Style information.
<p>

<h2>Caching</h2>

In order to enable fast access to large datasets without having to
retranslate them each time they are accessed, the FMEObjects gateway
supports a mechanism to cache features read from FME readers in
"Fast Feature Stores", a native vector format for FME with a spatial
index for fast spatial searches.  These cached files are kept in the
directory indicated by the OGRFME_TMPDIR environment variable (or
TMPDIR or /tmp or C:\ if that is not available). <p>

The cached feature files will have the prefix FME_OLEDB_ and a master index
is kept in the file ogrfmeds.ind.  To clear away the index delete all these
files.  Do not just delete some.<p>

By default features in the cache are re-read after 3600s (60 minutes).
Cache retention times can be altered at compile time by altering
the fme2ogr.h include file.<p>

Input from the SDE and ORACLE readers are not cached.  These sources are
treated specially in a number of other ways as well.<p>

<h2>Caveats</h2>

<ol>

<li> Establishing an FME session is quite an expensive operation, on a
350Mhz Linux system this can be in excess of 10s.<p>

<li> Old files in the feature cache are cleaned up, but only on subsequent
visits to the FMEObjects gateway code in OGR.  This means that if unused
the FMEObjects gateway will leave old cached features around indefinitely.<p>

</ol>

<h2>Build/Configuration</h2>

To include the FMEObjects gateway in an OGR build it is necessary to have
FME loaded on the system.  The <i>--with-fme=</i><b>$FME_HOME</b> configuration
switch should be supplied to configure.  The FMEObjects gateway is not
explicitly linked against (it is loaded later when it may be needed) so it
is practical to distribute an OGR binary build with FMEObjects support without
distributing FMEObjects.  It will just "work" for people who have FMEObjects
in the path.<p>

The FMEObjects gateway has been tested on Linux and Windows.<p>

<hr>

More information on the FME product line, and how to purchase a license for
the FME software (enabling FMEObjects support) can be found on the
Safe Software web site at <a href="http://www.safe.com/">www.safe.com</a>.
Development of this driver was financially supported by Safe Software.<p>

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