UAVs as Tools for Urban Planning in Uruguay

Irregular settlements, also known as别墅或者favelas，在城市规划中提出一个巨大的挑战。在收集数据时，是确定现有情况还是计划未来的项目，地形起着基本作用。不仅需要大量信息，而且通常也很难访问这些位置，这使得捕获信息比在古典地形的情况下更为复杂。摄影测量是在此类地区的理想方法，无人驾驶飞机（UAV）是此类空中调查的理想工具。请继续阅读有关乌拉圭该项目的详细信息。

(By Patricio Birriel and Raúl González)

从城市的角度来看，不规则定居点占据的城市地区是“冲突地区”。除其他问题外，土地权限不是合法的，法规不符合法规，城市服务是不规则的甚至失败的。此类领域正规化的计划始于社会和地形数据收集。良好的数据收集将构成更好的计划和预测，以便能够正规化情况。因此，地形数据的收集是这些领域未来城市发展项目的基本组成部分。所有新的细分，街道，卫生设施和其他服务都应进行预测，进而确保必须确保所有这些都可以在城市其他地区正常工作。不规则的定居点通常以高密度外壳，不规则形状和非常不稳定的结构为特征，并且可能位于容易发生洪水的地区。所有这些功能意味着地形数据的收集实际上非常复杂。因此，航空调查是最佳选择，而无人机系统获得的结果符合技术要求。

UAV surveys

In the department of Maldonado, Uruguay, a survey was conducted of the San Antonio squatter settlement which is in the draft stage. With a total area of 11.57 hectares divided into three sectors (A, B and C), it is an irregular settlement with high-density housing. The contractor, the Government of Maldonado, required information as the basis for urban projects. The survey was required to comply with very precise and rigorous technical specifications, and the contractor requested a survey of all the existing elements including houses, fences, passageways and streets, and waterways. Since the resulting data needed to meet the demands of future urban development, cadastre projects and engineering services, the tolerances were 3cm in planimetry and 5-6cm in altimetry. A survey of this area and with these features with classical topography (GPS and total station) would take 20 days of fieldwork with 10 days of processing, taking into account the need for surveyors to return to the site several times to capture missing points. Furthermore, the survey would surely be left with gaps in information due to the inaccessibility of certain locations. Traditional photogrammetry (using aircraft) would be considerably more costly to fly a small area and would need to use powerful cameras to achieve the required accuracy. UAV systems comply with all the technical requirements, fly at low altitude to produce very good accuracy, and are ideal for flying small areas.

Flight programming

This survey used the md4‐1000 UAV from the company microdrone. It is a rotating-wing UAV that has the necessary systems, such as GPS, gyroscope and radio link with the base station, to allow photogrammetric flight-path programming. The camera used is a SONY Nex7 24MP camera with a 16mm focal lens. To achieve the required urban cartography datasets, the flight altitude was set at 80m above the ground producing a theoretical accuracy on the ground of 2cm. The flight programming was carried out using the mdCockpit software (microdrone’s own software) that is based on the information provided by Google Earth. This allowed the UAV to fly at a constant height above the ground, keeping the photographic scale and homogeneous precision for all the work. Photogrammetric urban mapping using UAVs often employs both longitudinal and transverse coatings of the environment: 80% and 60% respectively. Due to the characteristics of the area, which is predominated by precarious low-rise dwellings, it was decided to decrease the coatings in order to obtain altimetric accuracy (the greater the longitudinal coating, the lower the altimetric accuracy), arriving at a longitudinal coating of 66% and an altimetric accuracy of 5.1cm in keeping with the precision required for this work. Cross overlay was set to 25%. Reduction of both longitudinal and transverse coating allowed a flight to be performed of shorter duration, fewer frames and shorter restitution. Based on these parameters, one flight was scheduled for each area of the settlement.

Support and control points

Support points are integral in the process because the overall accuracy of the work depends them. In urban surveys, the support points are traditionally taken once the flight has been performed by measuring the photo-identifiable points. Taking into account the difficult accessibility of certain parts of the area and considering traffic routes, support points were established while programming the flights, before flying commenced. White spray-painted crosses as markers ensured that the points were very clearly visible on the black or grey pavements. Establishing the support points prior to the flight enabled them to be distributed more effectively and to be placed in the areas that would be of greatest interest during processing. Once programmed, the flight points were placed in areas of the transverse overlap and each four models of the longitudinal overlap. These points were taken with RTK GPS dual frequency.

	SECTOR A	SECTOR B	SECTOR C
区域（公顷）	2.73	4.42	4.42
No. of flight lines	3	3	3
No. of images per line	11	15	18
No. of images	33	45	54
飞行时间（分钟）	13	15	17
No. of support points	16	21	25
计划准确性	2.5cm	1.7cm	2.1cm
高度准确性	5.6cm	5.0cm	5.6cm
表1，飞行计划：低飞行高度和高恢复准确性。

控制点是可识别的点，在放置支撑点时会采集。这些点位于模型错误将更高的区域中的支撑点之间的一半。这些要点是工作的质量控制。这些要点未提供给负责恢复原状的人员，因为一旦完成了空中三角测量和恢复原状处理，就将对其进行分析。来自控制点的数据必须在可接受的错误范围内。如果错误更大，则将讨论和纠正潜在的错误来源，以确保工作质量的统一性。

结论

由于大量的信息和高h precision required for surveys of irregular settlements for the purpose of urban projects, UAV photogrammetry is the ideal choice. The orthophoto mosaic produced from a low-altitude flight offers a number of details which are otherwise impossible to obtain. Thanks to the uniformity of work, the quality is guaranteed to meet the accuracy requirements with precision across the entire area. In such complex areas, with limited visibility between stations, that is very difficult to obtain when working with classical topography.

Authors

Patricio Birriel是一位工程师测量师，他从共和国大学工程学院（乌拉圭）毕业。他是UAV Surveying的联合创始人，UAV Surveying是一家乌拉圭地形服务公司，专门使用无人机进行空中调查。
e-mail:pbirriel@uavagrimensura.com.uy

Raúl González is a topographic engineer who graduated from the Polytechnic University of Madrid (Spain). He is co-founder of UAV Land Surveying which is specialised in UAV photogrammetry.