# ZED-F9P/GPS-RTK: RTCM UPDATE IN ROVER NOT PROVIDING EXPECTED ACCURACY **URL:** \ **Category:** Development Boards\ **Created:** [April 6, 2021, 6:35pm UTC](https://community.sparkfun.com/t/zed-f9p-gps-rtk-rtcm-update-in-rover-not-providing-expected-accuracy/41919 "2021-04-06T18:35:25Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![ashar7](https://avatars.discourse-cdn.com/v4/letter/a/ea5d25/32.png) [@ashar7](https://community.sparkfun.com/u/ashar7)\ **Post date:** [April 6, 2021, 6:35pm UTC](https://community.sparkfun.com/t/zed-f9p-gps-rtk-rtcm-update-in-rover-not-providing-expected-accuracy/41919/1 "2021-04-06T18:35:25Z")
I’m having issues getting the RTK-GPS system with the ZED-F9P to receive the advertised accuracy: - 2.5m without RTK - 0.010m with RTK I have setup the two ZED-F9P units in u-center, following the setup from "ZED-F9P Integration Manual (pg. 96-104),” which can be found here: [https://www.u-blox.com/sites/default/fi … 802%29.pdf](https://www.u-blox.com/sites/default/files/ZED-F9P_IntegrationManual_%28UBX-18010802%29.pdf). I have set the system up using I2C as the transmission means, not UART1. ZED-F9P is connected to the RedBoard via Qwiik connect, with a XBee Expansion board and XBee Pro Module used as communication between the Rover and Base (see Figure 1). ![Figure 1. Rover Setup with I2C.png](https://canada1.discourse-cdn.com/sparkfun/original/3X/1/a/1a5201580fb44d967a2801a919ed1d0011d9a278.png) Figure 1. Rover Setup with I2C The base station, that is on a tripod with a base plate, is using the code based on the following example: - Example2\_StartRTCMBase I am able to see the bytes being transmitted from the base station. I am passing the correction data across XBee through I2C and using the “pushRawData” method to update position. I was expecting to be able to get the resolution advertised with a base station and rover, yet I am not getting what I was expecting. I have tried multiple builds on the Rover from the examples provided ([https://github.com/sparkfun/SparkFun\_u- … es/ZED-F9P](https://github.com/sparkfun/SparkFun_u-blox_GNSS_Arduino_Library/tree/master/examples/ZED-F9P)). I need accurate latitude, longitude and altitude, yet none of these seem to work as expected: - Example5\_RelativePositioningInformation - Example3\_GetPosition (updated with pushRawData) - Example2\_NMEAParsing (updated with pushRawData) The system receives Latitude, Longitude and Altitude position. However, I am getting \> 5 m deviation. The data taken below is from a stationary rover sitting next to the base station. The data is varying randomly within a 6.56 m circle (see Figure 2 below). ![Figure 2. Position Deviation shown by Min & Max points.jpg](https://canada1.discourse-cdn.com/sparkfun/original/3X/d/9/d9aa2ba9cf9ea141ff4534055fd1c6e83be3bf5b.jpeg) Figure 2. Position Deviation showed by Max & Min points Can you please give me advice on what I may be missing? Hardware: - Sparkfun RedBoard (DEV-15123) - Sparkfun XBee Shield (WRL-12847) - XBee 3 Pro Modue - RP-SMA Antenna (WRL-15131) - 2.4GHz Duck Antenna RP-SMA - Large (WRL-00558) - GPS-RTK ZED-F9P Breakout (GPS-16481) - GPS/GNSS Embedded Antenna - 1m (SMA)(GPS-14987) Thanks, Katherine 😊 ---
**Author:** ![YellowDog](https://yyz1.discourse-cdn.com/sparkfun/user_avatar/community.sparkfun.com/yellowdog/32/1782_2.png) [@YellowDog](https://community.sparkfun.com/u/YellowDog)\ **Post date:** [April 6, 2021, 8:41pm UTC](https://community.sparkfun.com/t/zed-f9p-gps-rtk-rtcm-update-in-rover-not-providing-expected-accuracy/41919/2 "2021-04-06T20:41:39Z")
Try moving away from buildings and trees and see if that helps. ---
**Author:** ![ashar7](https://avatars.discourse-cdn.com/v4/letter/a/ea5d25/32.png) [@ashar7](https://community.sparkfun.com/u/ashar7)\ **Post date:** [April 6, 2021, 11:46pm UTC](https://community.sparkfun.com/t/zed-f9p-gps-rtk-rtcm-update-in-rover-not-providing-expected-accuracy/41919/3 "2021-04-06T23:46:52Z")
Thank you for your response. Sadly, I get the same result if I am placed in the middle of the yard. NOTE: I find the same variations happening whether I’m using u-center or running the program. Any advice would be appreciated!