Change the row and column number in the xml file manually is a hard work.
I know there is a template file here, but it's not convenient enough.
It is better to have a tool that can merge single images and automatically generate the xml file,
ShoeBox could do something like this, but it didn't support enough parameter to generate XML file that can be used directly。
You can have Opus do it for you. Make an icon set with standalone images and load it into Opus. If you then look under /dopuslocaldata\Icon Cache
and you'll find a merged PNG version and corresponding XML which you can use as the basis of the finished result.
I just find sprite sheet and XML of existing icon sets.
I still don't quite understand how to do it. Can you give a specific example?