Documentation of QGIS Python plugin brdrQ - Autocorrectborders

Description

The processing algorithm, named Autocorrectborders, is developed to automatically adjust thematic boundaries to reference boundaries. It searches for relevant overlap between thematic boundaries and reference boundaries, and creates a resulting boundary based on the relevant overlapping areas.

Input Parameters

The script requires the following input parameters:

Parameter	Description	Default	Optional
Thematic Layer	A (MULTI)POLYGON layer with a projected CRS (unit: meter) and a unique ID.	No default value, must be provided by the user.	No.
Thematic ID	Textual or numeric ID of the thematic layer used as a reference to the objects. This must be unique.	No default value, must be provided by the user.	No.
SELECT Reference Layer:	Selection of REFERENCE LAYER: The user can choose between a LOCAL REFERENCE LAYER (see parameters below), or on-the fly reference layers from GRB (Flanders, Belgium)	LOCREF: use of a LOCAL REFERENCE LAYER	Yes.
Reference Layer (when LOCREF selected)	A (MULTI)POLYGON layer with the same projected CRS (unit: meter).	No default value, must be provided by the user.	Yes.
Reference ID (when LOCREF selected)	Textual or numeric ID of the reference layer used as a reference to the objects.	No default value, must be provided by the user.	Yes.
Relevant Distance (meters)	Positive (decimal) number in meters. This indicates the maximum distance that the geometry is allowed to change.	3 (meters)	No.
PREDICTIONS (!slower!)	If True, the code will do a FULL SCAN of all relevant distances with an interval of 10cm to try to search for the best ‘predictions’.These are results where the output geometry is a stable result that could be the possible wanted result.- The resulting layer will use the prediction with the highest prediction score. Warning : When this option is used, the processing will be much slower, as a multitude of calculations are needed.	False	No
Prediction Strategy (when PREDICTIONS)	When PREDICTIONS, you can set Prediction Strategy to ALL (all predictions in result), BEST (the prediction with highest prediction score) or ORIGINAL (if multiple predictions,the original geometry is shown)	BEST	Yes.
Full Reference Strategy (when PREDICTIONS)	When PREDICTIONS, you can set if predictions that are fully aligned with the reference are prefered or not	PREFER_FULL_REFERENCE	Yes.
Processor	Choice of which processing-algorithm is used. Best to set it to AlignerGeometryProcessor as this chooses automatically the fastest algorithm	AlignerGeometryProcessor (Wrapper for DieussaertGeometryProcessor & NetworkGeometryProcessor)	No
OD_STRATEGY	This parameter determines how the algorithm deals with parts of the geometry that is not covered by reference data. Different strategies are available: EXCLUDE, ASIS, SNAP_INNER_SIDE, SNAP_ALL_SIDE	SNAP_ALL_SIDE (2)	No
FULL_OVERLAP_PERCENTAGE % (0-100)	Backup-parameter when the algorithm cannot decide if a reference is relevant to be taken into account. It falls back to the covered percentage.	50%	No
REVIEW_PERCENTAGE % (0-100)	Resulting geometries that change more than REVIEW_PERCENTAGE are categorised as ‘to_review’	10 (%)	No.
WORKING FOLDER	Folder to save the resulting geojson-files. By default empty, resulting in saving the geojson-files in a created folder.	Empty - a local folder is used	No
SHOW_INTERMEDIATE_LAYERS	If True, 2 additional layers are generated as output that visually represent the significant intersections and significant differences	False	No.
SHOW_LOG_INFO	If True, the logging of brdr is shown in the feedback-window.	False	No

Output Parameters

The script generates a GROUP layer with several output layers in the TOC:

CORRECTION_X_Y: a copy of the thematic layer with updated geometries, divided into categories (brdrq_state)
brdrQ_RESULT_X_Y: resulting geometries after alignment
brdrQ_DIFF_X_Y: differences (+ and -) between original and resulting geometry
brdrQ_DIFF_MIN_X_Y:differences (-) between original and resulting geometry
brdrQ_DIFF_PLUS_X_Y:differences (+) between original and resulting geometry
(optional) brdrQ_RLVNT_DIFF_X_Y: relevant differences (parts to exclude), used when processing the resulting geometry
(optional) brdrQ_RLVNT_ISECT_X_Y: relevant intersection (parts to include), used when processing the resulting geometry

The name includes which ‘RELEVANT_DISTANCE (X)’ and ‘REFERENCE (Y)’ is used

Example of Usage

Here is an example of how to use the script in Python:


{
                "INPUT_THEMATIC": themelayername,
                "COMBOBOX_ID_THEME": "theme_identifier",
                "RELEVANT_DISTANCE": 2,
                "ENUM_REFERENCE": 1,
                "INPUT_REFERENCE": None,
                "COMBOBOX_ID_REFERENCE": None,
                "WORK_FOLDER": 'brdrq',
                "ENUM_OD_STRATEGY": 1,
                "ENUM_PROCESSOR": 0,
                "THRESHOLD_OVERLAP_PERCENTAGE": 50,
                  "PREDICTIONS": 0,
                "FULL_REFERENCE_STRATEGY": 2,
                "PREDICTION_STRATEGY": 0,
                "REVIEW_PERCENTAGE": 10,
                "ADD_METADATA": True,
                "STABILITY": True,
                "ADD_ATTRIBUTES": True,
                "SHOW_INTERMEDIATE_LAYERS": True,
                "SHOW_LOG_INFO": False,
            }

processing.run('brdrqprovider:brdrqautocorrectborders', params)

TIPS

Set PREDICTIONS for the best results. This will analyse the full range of RELEVANT_DISTANCES (FULL SCAN), and returns the best stable results. A side-effect is that the processing-time is much slower. By default this parameter is set to False to have quicker results (QUICK SCAN), missing the better results.
Analyse your thematic dataset and try to gain insight into the ‘deviation’ (precision and accuracy from the reference layer):
- Where does the thematic data come from?
- when was it created,
- on what reference limits was it drawn at the time,
- Which drawing rules have been applied (e.g. accuracy of 0.5m)
- …

This allows you to gain insight into the ‘deviation’ and which RELEVANT_DISTANCE value can best be applied.

The current version of the script assumes that both the thematic layer and reference layer are in the same projected CRS with units in meter.
Thematic boundaries consisting of 1 or a few reference polygons are processed by the script in a few seconds. If the thematic boundaries cover a very large area (~1000 and reference polygons), it may take several minutes for the OUTPUT to be calculated. It’s best to let QGIS finish this processing before proceeding
In practice, we notice that large thematic demarcations are sometimes drawn more roughly (less precisely or inaccurately), so that a high RELEVANT DISTANCE is required to shift them to the reference file. For large areas that are drawn ‘roughly’, it is best to use a high RELEVANT_DISTANCE (e.g. >10 meters) and:
- OD-strategy EXCLUDE: if you want to completely exclude all public domain
- OD-strategy AS_IS: if you want to include all the covered public domain AS IS in the result
- OD strategy SNAP_SINGLE_SIDE: if you want to keep the public domain within the demarcation, but move the edges to the inner side of the thematic polygon
- OD strategy SNAP_ALL_SIDE: if you want to keep the public domain within the demarcation, but move the edges to the inner & outer side of the thematic polygon

OUTPUT - FIELDS

This sections lists fieldnames that can be found in the output layer and explains what this field is about.

Attribute	Type	Description
brdr_id	Integer	Internal unique identifier for the processed feature.
brdr_area	Double	The calculated area of the resulting geometry (\(m^2\)).
brdr_perimeter	Double	The total length of the boundary of the resulting geometry (\(m\)).
brdr_shape_index	Double	A complexity metric of the shape (e.g., compactness ratio).
brdr_stability	Boolean	Indicates if the geometry remains stable across multiple calculation iterations.
brdr_prediction_score	Double	Confidence score (%) of the alignment prediction.
brdr_prediction_count	Integer	Number of candidate matches found for the alignment.
brdr_evaluation	String	Categorization of the result (e.g., `prediction_unique`, `to_check_prediction_multi`).
brdr_relevant_distance	Double	The buffer or search distance used during the alignment procedure (\(m\)).
brdr_sym_diff_area_index	Double	The absolute area of the symmetrical difference between base and target (\(m^2\)).
brdr_sym_diff_area_index_perc	Double	The symmetrical difference expressed as a percentage of the total area.
brdr_diff_area_index	Double	The absolute area difference between input and output geometries (\(m^2\)).
brdr_diff_length_index	Double	The absolute difference in boundary length (\(m\)).
brdr_full_actual	Boolean	Flag indicating if the alignment covers the full extent of the actual feature.
brdr_remark	String	Automated logs or warnings generated during the geometry processing.
brdr_metadata	JSON/Object	Embedded SOSA/SSN metadata containing the lineage, sensors, and procedures used.