Question

What does the MRF2DCleaner transformer do?

Answer

MRF Geosystems Corporation (http://www.mrf.com) has produced cleaning software and made it available to FME users to apply to data as it is transformed between arbitrary input and output formats. MRFCleaners (available in 2D and 3D versions) repair geometry, particularly during data migration from CAD to GIS, and are built upon the MRFCleanFactory, which is an integration of MRF’s cleaning technology into FME.

Functionality

The MRF2DCleaner fixes geometric problems in input data such as line overshoots and undershoots within the user-specified tolerance. It is useful for multi-layer and multi-tolerance two-dimensional data cleaning. Typical applications include the correction of utility maps, parcel maps, topographic maps and resource maps as data is migrated from one system to another.

The MRF2DCleaner includes the following functionality:

• fuzzy tolerance
• extending lines
• weeding lines
• joining lines
• processing short elements
• removing gaps
• removing duplicates
• removing dangles
• performing conflation

The number of layers used in cleaning the data is determined by the number of different tolerance values of input features. Features that have the same tolerances are processed as being on the same layer. This allows feature data from a high-quality data source to be assigned a low tolerance and integrated with data from a lower-quality data source which would be given a larger tolerance.

Geometries such as path, polygon, donut, ellipse, elliptical arc, multi-area, multi-curve, text, and multi-text are converted to basic geometries such as point, line, path, arc or multi-point prior to the cleaning process. The cleaner understands and works with circular arcs. Input features with invalid geometries are ignored and deleted.

Spin-Off Transformers

The MRF2DCleaner transformer carries out multiple cleanup functions simultaneously. To enable single functions to be more easily implemented, the transformer has been split up into several sub-transformers.

• MRF2DConflator
• MRF2DDangleRemover
• MRF2DDuplicateRemover
• MRF2DExtender
• MRF2DGeneralizer
• MRF2DIntersector
• MRF2DJoiner
• MRF2DShortGeometryRemover

Transformer Fields

Cleaning tolerance is used as the default tolerance unless the Feature Tolerance Attribute is specified and valid. The minimum tolerance allowed is 0.0.

If Compute Intersections is set to Yes, intersections between all input features are computed, breaking arcs and lines wherever an intersection occurs. A fuzzy intersection is also created from geometries which are within one of the tolerance distances, but do not actually touch or cross.

If Correct Undershoots is set to Yes, arcs and lines that are within the specified tolerance are extended – while maintaining line-work direction. No intersections are created while doing this. This option does not process overshoots; a combination of Compute Intersections and Delete Short Geometries can serve this purpose.

If Delete Short Geometries is set to Yes, features that have lengths smaller than the specified tolerances are deleted.

If Remove Duplicate Geometries is set to Yes, duplicated features are deleted. Features are considered to be duplicates if their geometries are within tolerance and only features with a smaller tolerance will remain after cleaning.

If Generalize Lines is set to Yes, a number of vertices of lines are removed. The number of vertices removed is controlled by a weeding tolerance of the value of (Filter Factor * tolerance) or (Filter Factor * value of Feature Tolerance Attribute). The latter is always used when it is valid and the Feature Tolerance attribute is specified. The larger the value of weeding tolerance, the more vertices will be removed.

The default value of Filter Factor is 1.0 and the minimum value is 0.0.

If Join Geometries is set to Yes, then singly-connected features are joined to form longer ones. A pair of linear features become candidates for joining only when the two are singly connected at a given node or end point.

If Conflate Geometries is set to Yes, then the geometry of a feature can be changed to match that of another, if the two are approximately the same to begin with.

If Remove Dangles is set to Yes, then features that have at least one free end point and have lengths smaller than (Dangle Factor * tolerance) or (Dangle Factor * value of Feature Tolerance Attribute) are removed. The default value of Dangle Factor is 1.0 and the minimum is 0.0.

Module Workflow

This default workflow is suitable for most situations. However, using the individual modules, it is possible to create any number of customized workflows for specific projects and/or datasets (for example, in Workbench, by using a series of consecutive MRF2DCleaner transformers or custom transformers). It is important, however, to understand the data being processed and the desired end result.

What MRFClean is NOT Required For

Remarkable as it is, don't concentrate on using the MRF2DCleaner at the expense of other FME transformers. For example, when matching up boundaries that don't quite touch, the AnchoredSnapper is a much better solution (and at no extra cost).

The Intersector, Snapper and SelfIntersector are other examples of standard FME transformers useful in cleaning up geometries.