How Several GML Files Merge to One GML File?

Do they all have the same structure?

And do they contain geometry of the same geometry type (i.e. lines)?

 

 

My first suggestion would then be: with the Reader, read all those files at once and use the option 'Single Merged Feature Type'. Then use a Writer to write GML with the same Feature Type Definition as the Reader. And let it happen...

But it is not unusual (understatement) than there is more to do...

 

 

Goog luck on it!