Qt5 is required

Qt4 cannot be used anymore - see https://sourceforge.net/p/gpsbabel/mailman/message/36264877/

xmldoc/chapters/build.xml

@@ -35,8 +35,8 @@ You can grab a release from the <ulink url="http://www.gpsbabel.org/download.htm
 is required for all builds.  Mac and Windows users can download
 binaries from <ulink url="http://qt-project.org/downloads">Qt Downloads</ulink>
 Fedora or CentOS users may need to 'yum install qt-devel'.  Optionally, use qt5-base.  When in doubt, 'yum search qt' or 'yum search qt5' can help you find the correct package name
-Ubuntu users may need to 'apt-get install libqt4-core libqt4-dev'.
-Qt versions 4.6 and newer are supported.
+Ubuntu users may need to 'apt-get install qtbase5-dev'.
+Qt versions 5.2 and newer are supported.
 </para>
   <para><ulink url="http://libusb.sourceforge.net">libusb</ulink> 
 is recommended for OS/X and Linux if you want to use a USB Garmin or