If I added a GLONASS receiver to a Lowrance sonar (such as the HDS7 Gen3) would I be able to get better quality (higher resolution) maps and side scan mosaics with Reef Master?

If not, is there anything I can do to improve the resolution? A separate GLONASS saving position / time to a data file?

Better GPS positioning won't make any difference to the resolution of sidescan imagery, but it could possibly position the imagery more accurately. Headings are even more important than absolute positions and will be supported in RM2.0 (and are already supported in the Sonar Viewer), so the Point 1 is probably a better investment. The issue with running higher precision GPS through the HDS is that the SL2 log file format itself is limited to approximately 1m of resolution. This means that we always need to do some smoothing of the track in order to get acceptable sidescan mosaic results. The only way to get around this is to log position independently from the unit, and synchronise the two logs in post processing. We have done quite a lot of work on this, with some very good results, and will be including support for this within RM2 at some point (but likely not as part of the first RM2 release). There is a bit more information in this forum post.

Thanks Matt. Sounds like an Elite 7ti + TotalScan + Point-1 is about as good a system as I'll need for RM, at least for now. :)