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Data Processing (Coverage Aligner)

In this page one of the two possible scenarios defined for the use of the EMS is demonstrated. This is the Coverage Aligner : Two datasets should have identical geometry over a shared feature (such as a common administrative border), but the geometry varies.

The complete process is detaied here in order to goal two objectives:
  • Show the OpenJUMP WPS client usage
  • Show the Coverage Aligner functionality of the HUMBOLDT Edge Matching Service.

Load input datasets and show the problem to solve

1. Open the files to edit (File --> Open File...).


Loading datasets

Note: If datasets are in gml format, you will need to supply a Jump template. See here how to create a Jump template

2. In this case, Protected Areas from Portugal (dark green) and Spain (light green) are used. These datasets have been cleaned before, using the Dataset Cleaning process served by the EMS. See the Data Processing (Data Cleaning) description.


Datasets loaded

3. When zooming in, gaps between the two datasets become visible. This can be fixed by the Coverage Aligner Process. However, as the datasets have the same administration level (country level), none of the datasets can be seen as a ground truth. Therefore the Distribute-Errors mode should be used. All geometries will be transformed and no point or edge will be moved further than a client-specific amount (distance tolerance).


Gap in the Spanish Protected Area

Connect to WPS server

1. In the toolbar, click WPS Client -> Add WPS

2. Enter the URL to your WPS service. In this case, http://localhost:8080/wps/WebProcessingService. Press OK.

3. Check that that the service has succesfully been connected (bottom left) and execute the WPS (Click WPS Client --> Execute Process).

Note: These steps are described in detail in the Dataset Cleaning example. See the Data Processing (Data Cleaning) description. The connection to the WPS server is only needed one time per OpenJump work session.

Use Edge Matching Service

1. After click Execute Process a window with the processes provided by the service appears. Choose the HUMBOLDT Coverage Aligner Process. This process will remove the gaps and overlaps between both datasets. The Describe Tab is describing the process, i.e. DescribeProcess (OGC). Please read it.


DescribeProcess of the Coverage Aligner

2. Click the Execute tab. You must fill these input parameters:
  • reference_Geometry= input reference geometry dataset,
  • candidate_Geometry= input dataset which will be aligned to reference,
  • distanceTolerance= maximum distance of two edges to be matched,
  • reference_PositionalAccuracy= positional accuracy of the reference geometry,
  • reference_Scale= scale of the reference geometry,
  • candidate_PositionalAccuracy= positional accuracy of the candidate geometry,
  • candidate_Scale= scale of the candidate geometry.

The desciption of these inputs are given in the DescribeProcess document showed in the above step.
For applying distribute errors mode, i.e. that no dataset can act as a ground truth, the positional accuracy and the reference scale must be the same for both datasets. Therefore, you should fill the input parameters like follows:


Input parameters on Coverage Aligner (Distribute errors mode) example

When pressing the Execute Process button, it might take a long time (several minutes) depending on the size of the dataset. Please be patient.

See results

1. Results of Coverage Aligner in distributing errors mode. The gaps and overlaps are removed.


Results

2. Gaps and overlaps are not found between datasets.


Datasets aligned

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