VerticalExtent (GeoAPI normative 3.1-SNAPSHOT)

```
@UML(identifier="EX_VerticalExtent",
     specification=ISO_19115)
public interface VerticalExtent
```
Vertical domain of resource.
Since:

1.0
Departure from OGC/ISO specification:
ISO 19115 provides two ways to define a coordinate reference system, with the restriction that only one of those two ways can be used:
1. verticalCRS of type SC_VerticalCRS (from ISO 19111),
2. verticalCRSId of type MD_ReferenceSystem (from ISO 19115).
GeoAPI provides only the first way, because the MD_ReferenceSystem type has been intentionally omitted in order to have a single CRS framework (the ISO 19111 one).

Method Summary

Modifier and Type	Method	Description
`Double`	`getMaximumValue()`	The highest vertical extent contained in the resource.
`Double`	`getMinimumValue()`	The lowest vertical extent contained in the resource.
`VerticalCRS`	`getVerticalCRS()`	Provides information about the vertical coordinate reference system to which the maximum and minimum elevation values are measured.

- Method Detail
  - getMinimumValue
```
@UML(identifier="minimumValue",
     obligation=MANDATORY,
     specification=ISO_19115)
Double getMinimumValue()
```
    The lowest vertical extent contained in the resource.
    
    Returns:
    
    the lowest vertical extent.
  - getMaximumValue
```
@UML(identifier="maximumValue",
     obligation=MANDATORY,
     specification=ISO_19115)
Double getMaximumValue()
```
    The highest vertical extent contained in the resource.
    
    Returns:
    
    the highest vertical extent.
  - getVerticalCRS
```
@UML(identifier="verticalCRS",
     obligation=CONDITIONAL,
     specification=ISO_19115)
VerticalCRS getVerticalCRS()
```
    Provides information about the vertical coordinate reference system to which the maximum and minimum elevation values are measured. The CRS identification includes unit of measure.
    This property is conditional in ISO 19115-1:2016 but mandatory in GeoAPI because the alternative (verticalCRSId) is intentionally omitted in order to have a single CRS framework: the ISO 19111 one.
    
    Returns:
    
    the vertical CRS.