We conducted a baseline comparison for instrument calibration using GPS (Global Positioning System) and EDM (Electronic Distance Measurement) observations. The experiment was carried out at campus of the Autonomous University of Sinaloa (UAS) in Culiacan, Mexico. The main objective of this research was to establish a short (~125 m) baseline for calibration of geodetic- grade GPS and EDM instruments of different commercial brands to validate the precision specifications offered by the manufacturers of such instruments. We compared three types of geodetic-grade GPS receivers: Topcon Hiper Lite +, Ashtech Z-Xtreme and Leica SR500 and three types of EDM: Topcon GTS-236W, Pentax R-326EX and Leica TC-407. For the experiment, the baseline components were computed by using ionosphere-free double-difference (DD) GPS carrier phase observations processed using the PAGES software (Program for the Adjustment of GPS EphemerideS). The GPS data were processed with a 1-second sampling rate, 10-degree cutoff angle, and precise GPS orbits disseminated by IGS (International GNSS Service). The length of the calibration baseline was also obtained by averaging 20 measurements of line length directly recorded by the three different EDM instruments. GPS results agree among different brands with differences of ±2 mm in contrast with the resulting EDM values that differ within ±3 mm.
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