CommonLocalReprojector

If attributes are not specified, all features will be reprojected to the same local coordinate system. If attributes are specified, each group of features will be reprojected to a local coordinate system centered on that group.

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present.

Process When Group Changes (Advanced): This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

Considerations for Using Group By

There are two typical reasons for using Process When Group Changes (Advanced) . The first is incoming data that is intended to be processed in groups (and is already so ordered). In this case, the structure dictates Group By usage - not performance considerations.

The second possible reason is potential performance gains.

Performance gains are most likely when the data is already sorted (or read using a SQL ORDER BY statement) since less work is required of FME. If the data needs ordering, it can be sorted in the workspace (though the added processing overhead may negate any gains).

Sorting becomes more difficult according to the number of data streams. Multiple streams of data could be almost impossible to sort into the correct order, since all features matching a Group By value need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, using Group By with Process At End (Blocking) may be the equivalent and simpler approach.

Note: Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.

Choose the local projection from the drop-down list based on whether preservation of distances or areas is more important. Choices are:

• AZMED (Lambert Azimuthal Equidistant)
• AZMEA (Lambert Azimuthal Equal Area)

This parameter determines how Z values will be handled:

• Ignore heights and leave them unchanged: Z values will not affect the reprojection and will not be changed.
• Heights are relative to the ellipsoid or geocentric: Z values will be treated as ellipsoid heights with the same units as the horizontal units (or meters, for geographic coordinate systems). If the source coordinate system is geocentric, coordinates will be converted to geographic+ellipsoid height before being processed.

Note: Note that rasters can only be reprojected in 2D (that is, with Ignore heights and leave them unchanged).