QGIS : Merge two layers using Raster calculator include NoData values 合併圖層

Press Ctrl+Alt+M open commander

Open Processing algorithm: Raster calculator

QGIS 2.10.x

• Main input layer 

Select first input layer ( as variable a, DEM, sea level == NoData )

Sea = white area

• Additonal layers 

Select second input layer ( as variable b, Bathymetry ) 

• Formula 

ifelse(gt(a,0), a, b)

if a > 0 then output = a else output = b

• Use NoData

Checked

• Result 

The resulting layer

Note :

If your Main input layer contains NoData values, where the region  will be ignored in the calculation.

You must check the option "Use NoData" so calculated correctly.