Prequel: Difference between revisions

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A Prequel is an [[Grid Overlay]] which serves as input for another (geographical) calculation model, in place of [[Key]]ed [[Attribute]] values.
A Prequel is an [[Grid Overlay]] which serves as input for another (geographical) calculation model, overriding [[Key]]ed [[Attribute]] feature values.


In most cases, a [[Grid Overlay]] calculation will reference the presence of [[Attribute]] values which are related to vector data, such as [[Construction]]s or [[Area]]s. This is then [[rasterization|rasterized]] to provide input for the calculation model. For a number of calculation models, it is possible to configure a Prequel instead. This is a [[Grid Overlay]], the output of which serves as that same kind of input.
In most cases, a [[Grid Overlay]] calculation will reference the presence of [[Attribute]] values which are related to vector data, such as [[Construction]]s or [[Area]]s. This is then [[rasterization|rasterized]] to provide input for the calculation model. For a number of calculation models, it is possible to configure a Prequel instead. This is a [[Grid Overlay]], the output of which serves as that same kind of input.
==Uses==
Prequels can be used for a number of use-cases. Some common examples include:
* Increasing the detail of input data by providing it as a nearly-analog grid rather than a discrete set of values through polygonal features.
* Feeding the output of a previous calculation (from an earlier run, or running in parallel) into a following calculation.
* Including the effects of a geographical [[Action]] via a [[Combo Overlay]] in a controlled way in the input for a following calculation.
==Prequel calculations==
Any kind of [[Grid Overlay]] can serve as a Prequel. This allows for great flexibility, but also means care must be taken to select a prequel which has the correct type of data. For example, using a [[Combo Overlay]] to precompute [[Water level (Water Overlay)|water levels]] for a [[Water Overlay]] makes perfect sense. However, incorrectly precomputing the water depth rather than the water level will cause significantly different water initialization.
Prequel calculations are automatically [[calculation cycle|performed in order]]. Any [[Grid Overlay]] which relies on a Prequel will be computed after their Prequels are computed.
Any [[Warnings (Grid Overlay)|warning]]s which occur in Prequels are also reported as a warning in the [[Grid Overlay]] which relies on that Prequel's results.
==Examples==
A number of how-to's available are examples of how Prequels can be used to either compute more complex input for calculation models, or further process the output of other calculation models.
* [[How to create an evacuation routes overlay]]
* [[How to use a WMS to estimate foliage (Heat Overlay)]]
* [[How to set up pre-initialized water levels (Water Overlay)]]
{{article end
|notes=
* Circular references in Prequels are prohibited. An Overlay cannot be its own Prequel, be a Prequel to its own Prequel, etc.
|seealso=
*[[Prequels (Combo Overlay)]]
*[[Prequels (Heat Overlay)]]
*[[Prequels (Subsidence Overlay)]]
*[[Prequels (Traffic Noise Overlay)]]
*[[Prequels (Travel Distance Overlay)]]
*[[Prequels (Water Overlay)]]
*[[Prequels (Watershed Overlay)]]
*[[Prequels (Waterwijzer Overlay)]]
}}

Revision as of 13:11, 19 May 2022

This article is a stub.

A Prequel is an Grid Overlay which serves as input for another (geographical) calculation model, overriding Keyed Attribute feature values.

In most cases, a Grid Overlay calculation will reference the presence of Attribute values which are related to vector data, such as Constructions or Areas. This is then rasterized to provide input for the calculation model. For a number of calculation models, it is possible to configure a Prequel instead. This is a Grid Overlay, the output of which serves as that same kind of input.

Uses

Prequels can be used for a number of use-cases. Some common examples include:

  • Increasing the detail of input data by providing it as a nearly-analog grid rather than a discrete set of values through polygonal features.
  • Feeding the output of a previous calculation (from an earlier run, or running in parallel) into a following calculation.
  • Including the effects of a geographical Action via a Combo Overlay in a controlled way in the input for a following calculation.

Prequel calculations

Any kind of Grid Overlay can serve as a Prequel. This allows for great flexibility, but also means care must be taken to select a prequel which has the correct type of data. For example, using a Combo Overlay to precompute water levels for a Water Overlay makes perfect sense. However, incorrectly precomputing the water depth rather than the water level will cause significantly different water initialization.

Prequel calculations are automatically performed in order. Any Grid Overlay which relies on a Prequel will be computed after their Prequels are computed.

Any warnings which occur in Prequels are also reported as a warning in the Grid Overlay which relies on that Prequel's results.

Examples

A number of how-to's available are examples of how Prequels can be used to either compute more complex input for calculation models, or further process the output of other calculation models.