This can be done with a cold reboot. Use;

echo -e -n "\xb5\x62\x06\x04\x04\x00\xff\xff\x02\x00\x0e\x61" > /dev/serial0

The HDOP value can be used to determine the accuracy of the GPS position.  Lower is better.

The HDOP can be seen when using gpsmon. The image below has HDOP highlighted;
The HDOP can also be found in the GSA sentence.  Below it is shown as 1.3;

$GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39

A HDOP value of 1 or below would give you an accuracy of about 2.5m.

See here for more information.

The NMEA sentence update rate can be increased to 10Hz(10 times a second). The default is 1Hz (Once a second).

When increasing the update rate, you will also need to increase the baud rate.

To change the baud rate to 115200;

echo -e -n "\xB5\x62\x06\x00\x14\x00\x01\x00\x00\x00\xD0\x08\x00\x00\x00\xC2\x01\x00\x07\x00\x03\x00\x00\x00\x00\x00\xC0\x7E" > /dev/serial0

If you need to update the speed on the Raspberry Pi serial port, you can use;

stty -F /dev/serial0 115200

To increase update rate to 2Hz;

echo -e -n "\xB5\x62\x06\x08\x06\x00\xF4\x01\x01\x00\x01\x00\x0B\x77" > /dev/serial0

To increase update rate to 5Hz;

echo -e "\xB5\x62\x06\x08\x06\x00\xC8\x00\x01\x00\x01\x00\xDE\x6A" > /dev/serial0

To increase update rate to 10Hz;

echo -e "\xB5\x62\x06\x08\x06\x00\x64\x00\x01\x00\x01\x00\x7A\x12" > /dev/serial0

In uCenter, the setting can be found under UBX -> CFG -> RATE

The UBX protocol is documented here.

If you see this message in the output from the GPS;

This is the GPS telling you that it is receiving data on the serial port, but it doesn’t recognize it.

The cause is most likely due to echo being enabled on the Raspberry Pi serial port.

Echo can be disabled with;

The GPS module can be put to sleep by sending a UBX command to the GPS module.

To put it to sleep;

echo -e -n "\xB5\x62\x06\x57\x08\x00\x01\x00\x00\x00\x50\x4F\x54\x53\xAC\x85" > /dev/serial0

To wake it up;

echo -e -n "\xB5\x62\x06\x57\x08\x00\x01\x00\x00\x00\x20\x4E\x55\x52\x7B\xC3" > /dev/serial0

The UBX protocol is documented here.

Below are the strings used to turn on or off specific NMEA sentences. This is done using the UBX protocol.

The first line for each sentence below is to disable the sentence and the second line is to enable it again

GxGSV

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x03\x00\x00\x00\x00\x00\x00\x02\x38" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x03\x00\x01\x00\x00\x00\x00\x03\x3D" > /dev/serial0

GxVTG

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x05\x00\x00\x00\x00\x00\x00\x04\x46" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x05\x00\x01\x00\x00\x00\x00\x05\x4B" > /dev/serial0

GxGLL

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x01\x00\x00\x00\x00\x00\x00\x00\x2A" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x01\x00\x01\x00\x00\x00\x00\x01\x2F" > /dev/serial0

GxGSA

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x02\x00\x00\x00\x00\x00\x00\x01\x31" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x02\x00\x01\x00\x00\x00\x00\x02\x36" > /dev/serial0

GxGGA

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x00\x00\x00\x00\x00\x00\x00\xFF\x23" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x00\x00\x01\x00\x00\x00\x00\x00\x28" > /dev/serial0

GxRMC

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x04\x00\x00\x00\x00\x00\x00\x03\x3F" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x04\x00\x01\x00\x00\x00\x00\x04\x44" > /dev/serial0

GxZDA

echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x08\x00\x01\x00\x00\x00\x00\x08\x60" > /dev/serial0
echo -e -n "\xB5\x62\x06\x01\x08\x00\xF0\x08\x00\x00\x00\x00\x00\x00\x07\x5B" > /dev/serial0

Below is where these can be found in uCenter.UBX->CFG->MSG

The UBX protocol is documented here.

The baud rate can be changed by sending a UBX command to the

GPS module.
To change the baud rate to 115200;

echo -e -n "\xB5\x62\x06\x00\x14\x00\x01\x00\x00\x00\xD0\x08\x00\x00\x00\xC2\x01\x00\x07\x00\x03\x00\x00\x00\x00\x00\xC0\x7E" > /dev/serial0

If you need to update the speed on the Raspberry Pi serial port, you can use;

stty -F /dev/serial0 115200

To change back to 9600;

echo -e -n "\xB5\x62\x06\x00\x14\x00\x01\x00\x00\x00\xD0\x08\x00\x00\x80\x25\x00\x00\x07\x00\x03\x00\x00\x00\x00\x00\xA2\xB5" > /dev/serial0

The other baud rates are;
19200;

echo -e -n "\xB5\x62\x06\x00\x14\x00\x01\x00\x00\x00\xD0\x08\x00\x00\x00\x4B\x00\x00\x07\x00\x03\x00\x00\x00\x00\x00\x48\x57" > /dev/serial0

38400;

echo -e -n "\xB5\x62\x06\x00\x14\x00\x01\x00\x00\x00\xD0\x08\x00\x00\x00\x96\x00\x00\x07\x00\x03\x00\x00\x00\x00\x00\x93\x90" > /dev/serial0

57600;

echo -e -n "\xB5\x62\x06\x00\x14\x00\x01\x00\x00\x00\xD0\x08\x00\x00\x00\xE1\x00\x00\x07\x00\x03\x00\x00\x00\x00\x00\xDE\xC9" > /dev/serial0

Below is where this can be set using uCenter. UBX -> CFG -> PRT

The UBX protocol is documented here.