raster - QGIS GRASS Missing Dependancy

I want to perform a view shed analysis in QGIS using GRASS 7 r.viewshed.

When I double click on r.viewshed in GRASS GIS 7 commands in the processing toolbox of QGIS I get the following message:

Missing dependency.This algorithm cannot be run :-( This algorithm requires GRASS GIS 7 to be run. Unfortunately, it seems that GRASS GIS 7 is not installed in your system, or it is not correctly configured to be used from QGIS Click here to know more about how to install and configure GRASS GIS 7 to be used with QGIS

GRASS commands seem to work such as r.los but the GRASS 7 commands don't.

I am using a MAC OS X Mavericks with the latest version of QGIS 2.4.0 Chugiak.

Answer

GRASS 7 is still in a beta release stage. The Kyngchaos.com package is a stable release of QGIS, which does not yet include GRASS 7 internally. You can get a copy using the Homebrew package manager and the OSGeo4Mac tap:

1. 
   

   Install Xcode, Xcode Command Line Tools and Homebrew

   
   


2. 
   

   Then, in Terminal run: brew install osgeo/osgeo4mac/grass-70 (if your HOMEBREW_PREFIX is the default /usr/local then a pre-built binary will be installed on Mavericks)

   
   


3. 
   

   Set in QGIS, in Processing->Options menu's dialog: Providers->GRASS GIS 7 commands->GRASS 7 folder to (your HOMEBREW_PREFIX path)/opt/grass-70/grass-base

   
   

Occasionally, you may have to open and close the Processing Options dialog to get Processing to remember settings after a relaunch of QGIS, at least on Mac (current bug).