It's easiest to use the build_skymap.sh script in the parent directory, but if you want to understand the steps:

The following procedure will regenerate the binary star data:

1. Install protoc from https://developers.google.com/protocol-buffers/docs/downloads
2. Regenerate the Java protocol buffer with ./compile_proto.sh. This step and the one above can be skipped if no changes to the app's source.proto file have been made.
3. Build the utilities with ./gradlew assemble installDist from the stardroid directory.
4. Gradle's application plugin generates the wrong classpath for the utilities. Fix it by going into tools/build/install/datagen/bin/datagen and removing the apk from the classpath. Leave the root installation directory $APP_HOME/lib.
5. Convert the star and messier data files to text protocol buffers with ./generate.sh from the tools directory.
6. Recompile the App to ensure that string IDs are up to date. You can do this just by running ./gradlew assemble.
7. Replace the text protocol buffers with versions that include the string resource ids from the R.java file with ./rewrite.sh from the tools directory
8. Finally run ./binary.sh from the tools directory to convert the ascii proto bufs to binary ones (and put them in the right directory).