**2. Evaluation Methods**

This section describes the methods and metrics of data quality check, the analysis indicators for satellite visibility of different systems, and the positioning strategies of DD network and PPP processing, as well as the evaluation indicator for DD network solutions and PPP solutions.

#### *2.1. Data Quality Check*

The measurement quality assessment aimed to detect the GLONASS and GPS poor observations, which further affect the positioning performance of different combinations. TEQC [21] toolkit was employed to perform the quality assessment of GLONASS and GPS

L1 and L2 signals, which are used for performance assessment. The quality check was conducted using the following indicators:


$$\text{MP1} = \text{P}\_1 - \left(1 + \frac{2}{\alpha - 1}\right) \mathcal{O}\_1 + \left(1 + \frac{2}{\alpha - 1}\right) \mathcal{O}\_1 \tag{1}$$

$$\text{MP2} = \text{P2} - \left(\frac{2\alpha}{\alpha - 1}\right) \mathcal{Q}\_1 + \left(\frac{2\alpha}{\alpha - 1} - 1\right) \mathcal{Q}\_2 \tag{2}$$

where MP1 denotes the multipath effect on L1 frequency and MP2 indicates the multipath effect on L2 frequency; P1 and P2 denote the pseudorange observations at L1 and L2 frequencies, respectively; ∅<sup>1</sup> and ∅<sup>2</sup> denote the carrier phase observations of L1 and L2 frequencies, respectively; α = f1 f2 2 , where f1 denotes the L1 frequency, and f2 denotes the L2 frequency.
