[rrd-users] Can a graph be created that aggregates a set of (identically structured) rrd files?

[Jeff Gilmore]

Hi folks,
	I am new to RRD and still trying to wrap my mind around the power of this excellent tool.  I am working on an application to use RRD to store electricity meter data for a group of homes.  I am expecting to create an RRD file for each home, and it will have a number of RRA's defined for various time periods.

In addition to displaying the individual house data graphs, I would like to also create graphs that show aggregated results drawn from the house RRD files.  For example, I might show the combined power draw in watts for the 8 homes that make up a quadrant of my neighborhood, or show the total power draw from all 30 homes.  

Is there a reasonably-straightforward way to do this in RRD? 

Any suggestions will be appreciated.

Thanks,

Jeff