Figure 2
From: Real-time Kinematic Positioning of INS Tightly Aided Multi-GNSS Ionospheric Constrained PPP
Sky plots (azimuth & elevation) of available multi-constellation GNSS satellites at Taiyuan city, China on 25 April, 2015.
The subfigures (a) GPS; (b) BeiDou; (c) GLONASS; (d) GPS + GLONASS + BeiDou.
