Positional uncertainty for cadastre of urban land parcels by linear measurements
ISBN 978-85-88783-11-9
Authors
1de Araujo Limoeiro, M.; 2Araujo de Jesus, T.; 3Caldas Brandão, A.
1UFBA Email: milenaalimoeiro@gmail.com
2UFBA Email: araujotaiane@outlook.com
3UFBA Email: acaldas@ufba.br
Abstract
This paper describes the results from analysis of point positioning uncertainty in territorial limits using the trilateration method. The observations adjustment was performed by least square method. The procedure advantage is it offers the possibility to evaluating the quality of measurements and to quantify positional error. In the methodology analyzed in the experiment majors and minors semi-axis lengths of error ellipses for each point coordinate was computed. The major semi-axis length ranged from 0.001 to 0.106 m, and its average was 0,032 m. As the minor semi-axis length of the ellipses ranged from 0.001 to 0.068 m, and its average was 0.023 m. The absence of a land survey and mapping quality has been a common problem in most Brazilian cities. In this context, the Multipurpose Territorial Cadastre is a great tool to supporting municipal administrative actions. However, the real information about the territorial occupation needs to be provided with clarity and reliability to allow the multipurpose utilization. This paper presents an efficient and effective methodology for cadastral parcel measuring that combines low cost and high quality in acquisition database for building a land cadastral system and allows the acquisition of information from inside the land parcel. In the experiment was simulated, using the software LibreCAD, a measurement for cadastral survey of a typical urban block with 11 territory parcels. To perform the adjustment of a measurement network becomes necessary the adoption of control points. In this experiment was adopted as reference the coordinates of all facades points. In order to define the geometry of land parcels was simulated the measurements. By using LibreCAD were extracted, from an urban parcels design, horizontal distances between points that define the boundary of each plot. In field these measures can be obtained by fiber tape. Then, from this distances was calculated the horizontal angles between consecutive alignments of the plots by the rope method. In this method are measured two distances (d1 and d2), under the alignments that form the angle, and the distance between these points (D). Then the horizontal angle (θ) is calculated. The accuracy of the horizontal angles obtained by rope method varies according to how the parcel limit is defined. LIMOEIRO et al. (2012) have found that the average standard deviation of the angles obtained by rope method was 00 ° 05' for limits defined by smooth walls, 00 ° 16 ' for limits defined by stone wall and 00 ° 07 for limits defined by grade. LIMOEIRO et al. (2012) also measured as the angular uncertainties can influence in the final positioning. In accordance with BRANDÃO (2003) has suggested was adopted as tolerance ± 10cm for the uncertainties positional. Based on the simulated data described and discussed in section 2, the software Adjust Version 5.10 CG Consulting (educational use) was used for the observations adjustment by least squares method. The adjustment output file contains horizontal coordinates of all points and their error ellipses at 95% level of confidence. The results obtained by the adjustment proves that the method studied can be suitable for executing cadastral measurements from territorial parcels in urban areas. As advantages highlight two main aspects, the first refers to the simplicity and low cost of data collection using only linear measures obtained by tape. The another one is the possibility of evaluating measurements quality from the error ellipses of all point, what is essential to making decision about levels of acceptance and rejection of measurements. References: BRANDÃO, A. C. O principio da vizinhança geodésica no levantamento cadastral de parcelas territoriais. 2003. Universidade Federal de Santa Catarina , Florianópolis, 2003. LIMOEIRO, M. A., JESUS, T. A., BRANDÃO, A.C. Incerteza do ângulo horizontal e do posicionamento 2D em poligonais pelo método da corda (poligonação à trena). VI GEONORDESTE. Aracaju,
Keywords
cadastral survey; positional uncertainty; urban land parcels