The RTKT file extension is used by the GeoVisu for data downloaded form the Royaltek. File is in binary format.
How to open:
The best way to handle GIS files is to use their native software. If you do not have access to it, look for some 3rd party alternatives with broad format support or perhaps a converter that would allow you to export the data to some interchange format.For general information try to look at:Basic info how to open GIS, GPS or map files
How to convert:
Special GIS converter exist and may help users to transfer or transform their maps and other navigation data between programs or devices.
For general information try to look at:Basic info how to convert GIS, GPS or map files