To build Orion Viewer from command line you will need:
android-sdk-r21
apache-ant 1.8
Specify path to android-sdk in 'orion-viewer/local.properties'
Use 'orion-viewer/local.properties.sample' as example.
There is a build script in 'orion-viewer' folder named 'build.xml'.
To build project run 'ant release' from this folder.
For native build see ReadMe file in "orion-viewer/jni" folder