Merge pull request #235 from noritada/build-option-help-improvements

Update help text for build options that affect file encoding/decoding capability

CMakeLists.txt

@@ -24,10 +24,10 @@ option(DISABLE_TIMEZONE "Disable posix Timezone?" off)
 option(DISABLE_ALARM "Disable Alarm?" off)
 set(USE_NAMES "NCEP")
 option(USE_G2CLIB "Use g2c lib?" off)
-option(USE_PNG "Use PNG?" off)
-option(USE_JASPER "Use Jasper?" off)
-option(USE_OPENJPEG "Use OpenJPEG?" off)
-option(USE_AEC "Use AEC?" off)
+option(USE_PNG "Use PNG to enable decoding of GRIB2 data with PNG packing (packing type 41)." off)
+option(USE_JASPER "Use Jasper to enable encoding/decoding of GRIB2 data with JPEG 2000 packing (packing type 40)." off)
+option(USE_OPENJPEG "Use OpenJPEG to enable encoding/decoding of GRIB2 data with JPEG 2000 packing (packing type 40)." off)
+option(USE_AEC "Use AEC to enable encoding/decoding of GRIB2 data with CCSDS packing (packing type 42)." off)
 option(FTP_TEST_FILES "Fetch and test with files on FTP site." OFF)
 option(FTP_LARGE_TEST_FILES "Fetch and test with very large files on FTP site." OFF)
 option(FTP_EXTRA_TEST_FILES "Fetch even more large files from FTP and test them." OFF)