This research delves into Global Navigation Satellite Systems (GNSS) positioning accuracy, focusing on GPS, GLONASS, and their combined utility to evaluate GLONASS as an independent system in case GPS is down. The study spans three phases. First, data from stations located in Port Said, analyzed using relative positioning technique, GPS shows an average coordinate deviation of 0.32 millimeters for GPS-only scenarios, while GLONASS exhibits 1.045 millimeters for GLONASS-only scenarios. Merging both narrows this gap, especially in shorter baselines. Second, an extensive dataset over three years from eight Egyptian stations, using GPS and GLONASS as references, shows that GPS consistently provides better three-dimensional accuracy in most stations with close values. Finally, employing Precise Point Positioning (PPP) techniques, the study rigorously compares three processing software solutions (PPPH, PPP-ARISEN, PRIDE-PPPAR) with the same dataset. PRIDE-PPPAR closely aligns with BERNESE software accuracy, followed by PPP-ARISEN and PPPH. These findings suggest that GLONASS alone can be used for many applications, and open-source PPP software can be employed with acceptable accuracy.