I have finally found a way to use nautical charts for plotting ROV position.
Thanks to OpenCPN Håkan!
Ship is showed on same chart, so moving ship after ROV is now easier.
Same info can be sent to plotter at helm.
Info like distance to ROV is possible
-OpenCPN software with charts.
-Underwater GPS to have position of ROV into PC.
-Basic GPS (and headíng sensor) to position ship as usual, via serial port or UDP etc
Trick to get ROV position is to use NMEA string $RATLL via UDP for sending ROV position to OpenCPN. OpenCPN then thinks You are plotting a radar MARPA taget and displays that.
String is sent from Waterlinkeds modified Python NMEAOutput module and looks like this:
Where 01 is ship ID, lat, long, Shipname(ROV), GPS time, T is tracked, *75 is NMEA checksum
Below is testing via Waterlinkeds demoserver