# FMEObjects Gateway

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 accessable.

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 (ie. 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:

- 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.

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

- 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.

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.

## Caching

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).

The cached featur 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.

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

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

## Caveats

1. Establishing an FME session is quite an expensive operation, on a 350Mhz Linux system this can be in exceess of 10s.

2. 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 indefinately.

## Build/Configuration

To include the FMEObjects gateway in an OGR build it is necessary to have FME loaded on the system. The --with-fme=$FME_HOME 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.

The FMEObjects gateway has been tested on Linux and Windows.

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 www.safe.com. Development of this driver was financially supported by Safe Software.