2DGridAccumulator

This transformer accepts any feature.

The grid of point or polygon features covering the bounding box area of the input features.

Features with non-numeric attributes for Column Width and Row Height or Number of Horizontal Tiles and Number of Vertical Tiles are output through this port. However, once a feature with numeric values in these attributes is received, all following features will use these same attribute values and will not be rejected.

Rejected features will have an fme_rejection_code attribute with one of the following values: INVALID_GEOMETRY_TYPE, INVALID_PARAMETER_SURFACE_NORMAL_DEVIATION, INVALID_PARAMETER_THICKNESS.

The input features may be partitioned into groups based on attribute values and one bounding box feature is output for each group. If you do not specify any Group By attributes, all input features will be processed together and a single bounding box will be output.

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.

Specifies how the grid size will be defined. Cell Size will enable the Column Width and Row Height parameters, while Number of Cells will enable the Number of Horizontal/Vertical Tiles parameters.

Chooses a starting corner for the purposes of numbering rows and columns. Also, when Grid Type is Cell Size, the last row and/or the last column may extend beyond the bounds of the input features; here the “last” row or column is the one opposite the Starting Corner.

Choose point or polygon features.

Choosing Polygons will generate rectangular boxes with the specified column width and row height.

If Points (Corners) is selected, the corners of all the rectangles in the grid will be output. Points (Centers) will generate the middle point of each rectangle.

Note that there will be more features output for Points (Corners) than for either of Polygons and Points (Centers), since there will be one additional row and one additional column.

The Column Width and Row Height parameters specify in ground units the distance between output points in the grid or the width and height of the output polygons.

Important: If you use attribute values as the Column Width and/or Row Height, only the attributes of the first encountered feature of each group are used. These attributes will be ignored for any following features from the same group.

These optional parameters specify a "seed point" from which cells will be generated. Note that it is permissible to specify a value for only one of these parameters—not necessarily both.

The Number of Horizontal Tiles and Number of Vertical Tiles parameters are required when the Grid Type parameter is Number of Cells, and allow you to specify how to tile the input data (for example, 5 horizontal tiles and 5 vertical tiles).

Important: If you use attribute values as the Number of Horizontal Tiles and/or Number of Vertical Tiles, only the attributes of the first encountered feature of each group are used. These attributes will be ignored for any following features from the same group.

If Column Attribute or Row Attribute are specified, attributes will be added to each output tile that identify the position of that tile in the input raster. These indices are zero-based, beginning at the specified Starting Corner.

If Column Attribute or Row Attribute are specified, attributes will be added to each output tile that identify the position of that tile in the input raster. These indices are zero-based, beginning at the specified Starting Corner.