I need to precisely set the size of the slam map generated by slam gmapping on Stage. My goal is to save the slam map with map_server. My gmapping parameters are as follows:

 <param name="delta" value="0.1" />
 <param name="xmin" value="-15.0" />
 <param name="xmax" value="15.0" />
 <param name="ymin" value="-15.0" />
 <param name="ymax" value="15.0" />

I want the saved map to be 300x300 pixels. However, it is saved as 288x288. Where are the 12 missing pixels? How can I retrieve them?