Precise positioning in London’s sky

Author:Renata Barradas Gutiérrez

城市地标不是在一夜之间建造。在计划，设计和施工之间，还有其他关键活动 - 就像监视和定位一样 - 同时进行。

22 Bishopsgate，一个287-metre-tall skyscraper, rose through the air in London’s financial district in the United Kingdom. Planned with the ambition to be the capital’s first ‘vertical village’, 22 Bishopsgate isLondon’s second tallest building.

To construct the cores that make this landmark rise, Careys Civil Engineering, a well-known construction company with a proven track record of delivering projects that enhance the built and natural environments of communities and infrastructure in the United Kingdom and Ireland, delivered the concrete works using a self-erecting jump form system – the first of its kind to be used in the UK.

Building62 storeys, with a floor space of more than120,000 square metresrequired Careys Civil Engineering to pour58,000 cubic metres of concreteand use7,500 tonnes of reinforcement. Thriving on complex and challenging projects of this magnitude requires innovative methodologies

– just like the building positioning system developed for Careys Civil Engineering by Leica Geosystems. This tailor-made solution for jump form high-rise buildings was chosen by Careys Civil Engineering to provide reference coordinates to monitor and carry out the surveying tasks during construction.

Doing it the Careys’ and Geosystems’ way

The two core walls of 22 Bishopsgate were constructed by Careys Civil Engineering in a sequence of several concrete pours using a jump form system. Jump form systems are working platforms or rigs for fixing of the formwork, steel fixing and concreting. This system is suitable for the construction of multi-storey vertical concrete elements in high-rise structures.

每次跳跃或钻机的高程以建立一个新的水平后，Careys土木工程测量团队需要可靠的坐标来继续设置结构并验证核心的正确定位。自动定位系统Leica Geosystems创建的主要任务是在整个施工过程中获得精确可靠的坐标，而这些坐标不受建筑物的运输影响。

This tailor-made GNSS-based monitoring solution consisted of:

• SevenLeica GM30 GNSS receivers for monitoring
• SevenLeica AR10 GNSS antennae
• Leica GeoMoS Monitor
• Leica GNSS Spider software
• HxGN SmartNet reference station network
• Tiltmeters

With the above-mentioned hardware and software combination, Leica Geosystems developed a procedure, using GNSS observations combined with tiltmeters (precision inclination sensors), to obtain reliable coordinated points at the top of the formwork of the ascending skyscraper. Those coordinated points, or Active Control Points (ACP), are sighted by Leica Geosystems robotic total stations to setup its coordinates and orientation.

“在伦敦市中心的一定高度以上，地面控制点不再可用或可见。GNSS系统能够提供可靠的坐标，而无需地面控制，” Careys土木工程，工厂和车队部高级工程师Damien Watson说。

To set up the automated positioning system, GNSS stations were coupled with Leica Geosystems 360-degrees prisms, so the positioning information provided by the GNSS sensors was available to be used as reference points for the surveyors performing the survey of the core wall with Leica Geosystems robotic total stations.

固定在GNSS天线的相同位置的高精度倾斜度耦合到GNSS站，以跟踪GNSS天线的垂直度，以便在每个计算时提供最准确的坐标。SmartNet网络用于为钻机上的GNSS站提供参考坐标并计算基线。

确保流畅的数据流

To obtain the ACP, data was collected, stored and post processed with Spider Software at a dedicated PC to deliver the most accurate coordinates for the team. Spider is the control centre software where positioning information was computed. The data from the GNSS stations on the rig and data from the SmartNet Reference Network was combined to provide every six hours the most accurate set of coordinates for each point for Careys Civil Engineering team. Spider coordinates were automatically transferred to GeoMoS Monitor where they were transformed into local coordinates and adjusted based on tiltmeters data.

“The Leica Geosystems solution allowed for a fully-automated workflow and computation of the results and fast delivery of coordinates when required, optimising costs and time of operation for the surveying team compared to different methodologies,” said Watson.

此外，该团队能够实时检查蜘蛛界面中每个单点的卫星数量和数据质量。所有这些质量检查实时提供了高水平的定位测量准确性，使土木工程建造该地标所需的地标需要。

After each jump and processing period, new valid control points coordinates were available for the robotic total station to measure any mark or object in the structure. The Careys Civil Engineering team on site then proceeded to set up the robotic total station at the top level where all control points were visible.

The robotic total station determined its own position and orientation observing the control points and checking the results with the coordinates given by GeoMoS. In this way, the robotic total station observed all relevant points to be checked during the construction.

Building on the rise

Accurate and reliable positioning on the status of structures displayed as actionable data is crucial to make fast and informed decisions and react to potential problems. The GNSS-based monitoring system has proven so successful that Careys Civil Engineering will be using it in future projects, such as the construction of a new tower in Manchester.

“徕卡呈规则的解决方案automatically delivered reference coordinates to the surveying team when needed, and the accuracy got better and better while the structure was growing building confidence after every jump,”concluded Watson.