Function getRasterLayerInitialTransparency

getRasterLayerInitialTransparency(layerId): number
JMap.Map.getRasterLayerInitialTransparency

Return the initial transparency (defined on the layer style) for a given raster layer
Parameters
- layerId: JId
  The JMap layer id
Returns number
the initial transparency value
Throws
Error if layer not found or not a raster layer

Example
```
 // returns the initial transparency of raster layer id=4
 JMap.Map.getRasterLayerInitialTransparency(4)
```