Constructs a Delaunay triangulation based on input points and breaklines. That triangulation is then uniformly sampled to produce a raster digital elevation model (DEM raster).
These input features may be 2D or 3D. Other than points, lines and area geometries, they may also be raster, point cloud, and aggregate geometries.
2D features will be forced to 3D by adding a z value of 0. In most cases, all points extracted from this port will be found in the vertex pool of the underlying surface model. A minimum of 3 unique points are required to construct a surface model. Points with duplicate x and y values will be dropped.
These input features may be 2D or 3D, and may reside inside an aggregate structure.
2D features will be forced to 3D by adding a z value of 0. Breakline edges will be found in the edge pool of the underlying surface model. Sometimes, a breakline edge will be split up to allow an optimal triangulation of the surface model. Points with duplicate x and y values will be dropped.
This output port samples the underlying surface model according to the sampling rates specified in Output DEM X Cell Spacing, and Output DEM Y Cell Spacing, and produces a single raster feature consisting of evenly spaced 3D points arranged by rows and columns.
This parameter allows groups to be formed by attribute values. Zero or more attributes may be specified.
Input features with the same attribute values are placed into the same group. The transformer then operates independently on each group of input features.
If this parameter is left blank, the transformer will treat the entire set of input features as one 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.
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.
This parameter is used to determine which input points to add to the surface model as vertices. Specifying a value of 0 turns off vertex filtering.
Tip: A larger value will speed up surface model construction. The larger the value, the more input points will be filtered out. For input files with millions – or even billions – of points, it becomes essential to increase this value.
When a positive value for surface tolerance is specified, it works as follows. For each vertex that is being added to the model:
- If the x,y location is outside the 2D convex hull of the existing surface model, it is added to the model.
- If the x,y location is inside the 2D convex hull of the existing surface model:
- The difference between the z value from the existing surface model and the z value of the vertex is calculated.
- This difference is compared to the surface model tolerance.
- The vertex is only added to the surface model if the difference is greater than the surface tolerance; otherwise, the vertex is discarded.
This parameter is used for the output ports DEMPoints and DEMRaster when these output ports exist on the transformer. It is also used if DrapeFeatures are input to the model.
- AUTO: The transformer will calculate each output point automatically. The PLANAR method is used if the output point is within a surface triangle in xy and the CONSTANT method is used otherwise.
- PLANAR: Barycentric interpolation is used to determine the z value for each output point. If an output point is outside the 2D convex hull of the surface model, the output z value will be set to NaN (Not a Number).
- CONSTANT: The z value of each output point is set to the z value of the closest vertex in the underlying model.
These parameters specify the x and y sampling intervals for the output DEMPoints.
This parameter is used only when Interpolation Method is set to PLANAR, and it only affects the output port DEMRaster.
All output raster cells that fall outside the underlying surface model’s boundaries will be assigned the value of this parameter.
When this parameter is blank, it is interpreted as NaN (Not a Number).
Note: To ensure consistent raster output, it is highly recommended that you do not leave this parameter blank.
If a set of individual 3D points comprising a DEM is required, you should use the DEMGenerator.
- This transformer is unaffected by raster band and palette selection.
Editing Transformer Parameters
Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.
FME Licensing Level
FME Professional edition and above
This transformer was previously named DEMGridGenerator.
Associated FME function or factory: SurfaceModelFactory
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Tags Keywords: MBR "minimum bounding rectangle" raster grid generate DEM elevation numeric create point DEMRasterGenerator DEMGridGenerator pointcloud