GPS World

Tag: ETAFAT

  • Casablanca’s Medina buildings monitored during tunnel construction

    Casablanca’s Medina buildings monitored during tunnel construction

    Photo: ETAFAT/Spectra Geospatial
    Photo: ETAFAT/Spectra Geospatial

    Engineers are monitoring in real time the effects on Casablanca’s aging buildings during tunnel construction using a Spectra Precision GNSS receiver.

    Vibrations during the construction of a new 1,890-meter tunnel adjacent to Casablanca’s Old Medina, the 250-year-old section of the famed Moroccan city, challenged the stability of its historically important buildings.

    To monitor in real time the effects on the Medina’s aging buildings and to confirm that the construction work meets all engineering standards and guidelines, ETAFAT, a geospatial information acquisition and processing company, used the Nikon XF Total Station to perform more than 100 daily inspections. The ETAFAT team relied on optical targets placed on building facades whose coordinates were determined by forced centering to complete the inspections.

    The new Les Almohades tunnel, beneath the Boulevard des Almohades, runs parallel and adjacent to the old Medina. Together with its 380 meters of access roads, the twin-tube tunnel, which carries traffic in two unidirectional lanes in each tube, was constructed to reduce traffic congestion.

    According to ETAFAT engineers, the Nikon XF 1” with its fast autofocus function, saved considerable field time. The Nikon XF enabled fast collection of highly accurate observations throughout the monitoring and control of the planimetric and altimetric locations of the structure. The monitoring of the buildings during the various phases of the tunnel’s construction generated a large amount of data essential for understanding the consequences of the work and defining any necessary corrective measures.

    The Nikon FX 1,” with its advanced options and Survey Pro software, enabled survey teams to quickly yet accurately perform a variety of other essential field tasks.

    These tasks include digital terrain modeling (DTM), cubature calculations, coordinate geometry (COGO) topometric calculations and layout control with customized report generation. The use of Survey Pro software enabled ETAFAT engineers to fully integrate their total station work with their fleet of Spectra Geospatial SP60 GNSS receivers.

    The Nikon XF 1” is a mechanical total station that stands up to tough worksite conditions. It is designed to quickly capture accurate measurements, and it offers crisp, clear optics for sighting in both bright and low-light conditions.

    Its dual-color touchscreen displays run Survey Pro, Survey Basic and Layout Pro.

    It is also equipped to take advantage of the optional Trimble Protected L2P device for asset security to locate lost, stolen or missing equipment. Its hot-swappable batteries reduce downtime and a PIN enhances security in the field.

  • Mauritanian utility corridor being surveyed with SP60 GNSS receiver

    Mauritanian utility corridor being surveyed with SP60 GNSS receiver

    The Spectra Precision SP60 GNSS receiver has been selected to perform survey work for construction of a new 450-kilometer electric power transmission corridor.

    Connecting Mauritania’s two largest cities, the capital Nouakchott and to the south Nouadhibou, the 225/90Kv transmission line parallels the Atlantic Ocean as it traverses the Sahara Desert.

    The Mauritanian Electricity Company, SOMELEC, through its contracting company, awarded the sub-contract for surveying the transmission line and infrastructure to ETAFAT, a geospatial data acquisition and processing firm.

    Difficult work conditions, including high heat (over 45 degrees Celsius) and the lack of existing control points were key factors in ETAFAT’s selection of the SP60 receiver. Because of the absence of existing benchmarks along the entire corridor, the SP60 RTX feature played a key role to ensure homogeneity in the coordinate reference frame between the two cities.

    The RTX technology leverages real-time data from a global tracking station network with innovative positioning and compression algorithms to compute and relay satellite orbit, satellite clock and other system adjustments, transmitted to the SP60 via satellite or IP to deliver real time high-accuracy corrections, even in remote locations, the company said.

    ETAFAT tested the SP60 data with RTX corrections and obtained consistently successful results. The geodetic survey was related to several ground control points (GCP) used in airborne survey. The measurement itself was conducted using two methods, dependently: the classical statistical method, and the RTK GNSS method. The SP60 met or exceeded the required +/- 15 cm order of accuracy.

    According to baseline processing and adjustment reports, the SP60 delivered superior results under all conditions, and it did especially well under typical high temperatures of the Sahara Desert. Initialization was well within 5 to 10 seconds for RTK survey with radio signal coverage inside a 5 km radius.