Network<\/code>, that needs to reference many or all objects of a different type, e.g. NetworkLinks<\/code><\/li>\n- You are building up a hierarchy of objects such as
AdministrativeUnits<\/code>, with their upperLevelUnit<\/code> and lowerLevelUnit<\/code> references<\/li>\n- You need to use Merge or Join operations to determine relationships between objects, but these are computationally too expensive<\/li>\n<\/ul>\n
With a Collector, you can collect values in one place in your transformation project and then use these values in another place in the transformation process. Let's look at a recent project we've worked on to see how they work in practice.<\/p>\n
Please note that this article assumes you have working knowledge of hale\u00bbstudio and know the terminology<\/a>.<\/p>\n![\"A](\"https:\/\/wetransform.eu\/wp-content\/uploads\/2022\/05\/keyCollection.jpg\")
<\/p>\n
To use a collector, there are two to three steps:<\/p>\n
\n- Define the collector<\/li>\n
- Define where to apply values from the collector<\/li>\n
- Optionally, define Cell Execution priorities to make sure collected values are available when used<\/li>\n<\/ol>\n
We always collect values in the context of another transformation function. As of hale studio 3.2.0, these are the transformation functions that support the definition of collectors:<\/p>\n
\n- Groovy Scripts and Groovy Script (Greedy)<\/li>\n
- Groovy Retype<\/li>\n
- Groovy Merge<\/li>\n
- Groovy Join<\/li>\n
- Custom Functions<\/li>\n<\/ol>\n
In all of these functions plus the following ones, you can apply the collected values:<\/p>\n
\n- Groovy Create<\/li>\n
- Assign Collected Values<\/li>\n<\/ol>\n
With the upcoming 3.3.0 release<\/a>, you'll see more widespread support for the feature. Basically, most existing functions will allow collecting values, and we'll add more functions to assign them.<\/p>\nThe Use Case<\/h2>\n
This is the use case we are going to work on for this tutorial:<\/p>\n
\nWe need to create an INSPIRE Hydrographical Network<\/a> dataset from UK Meridian 2 data encoded in a specific schema, using a GML 2.1 encoding. Each river segment from the source will be transformed to a WatercourseLink<\/code>, and in addition, we'll create a Network<\/code> object that references all created WatercourseLink<\/code> features.<\/p>\n<\/blockquote>\n![\"The](\"https:\/\/wetransform.eu\/wp-content\/uploads\/2022\/05\/sourceAndTargetSchemas.png\")
<\/p>\n
You can take a look at the hale transformation project for this tutorial and download it, including source data, here at haleconnect.com<\/a>.<\/p>\nImplementation<\/h2>\nStep 1: Define the Collector in a Groovy Script<\/code><\/h3>\n\n- As always, first define the Type-level transformation function. On the source schema, pick
River<\/code>, on the target side, select WatercourseLink<\/code>. Click on the double arrow icon and select Retype<\/code>. Use the default values for the function.<\/li>\n- Now, select
fid<\/code> on the source and id<\/code> on the target feature type. Click on the double arrow icon and select Groovy Script<\/code>. Leave the parameters on the first page as they are and click Next<\/code> to proceed to the actual script editor. After you've entered the script, click Finish<\/code> to let the transformation execute.<\/li>\n<\/ol>\n![\"Use](\"https:\/\/wetransform.eu\/wp-content\/uploads\/2022\/05\/defineCollectorInGroovy.png\")
<\/p>\n
This is the actual script to use:<\/p>\n