UNE 148002 service

The UNE 148002 service was implemented over the existing WPS architecture. In order to check if the service respond as expected in the Spanish standard, we prepared an experiment with three essays: (1) point data and Euclidean measures, (2) line data and Hausdorff distance (HD), and (3) line data and single buffer method (SBM). For this experiment was considered the sampling scheme for isolated lots (ISO 2859-2)

For the first essay (point data and Euclidean measure) we used 32 points measured from the building layer of BTN25 as test data. The reference point dataset was created using building instances from BCA10. We picked up 32 points from a central region of the city of Huelva. The maximum distance between homologous points is about six meters. For the point evaluation we considered that the lot size is 10 times greater the measured points, i.e., lot size equal to 320 features. We considered 'faulty data' those points whose reach a Euclidean distance greater than a given tolerance. Using these

Figure 4.23. Response of an execute request to the NSSDA service (Xavier et al.

2015b).

parameters we ran the service for a set of values for LQ and tolerance, as shown in Table 4.34. For each pair of parameters (LQ, tolerance) the service defines the values of 'Sample size / Acceptance' using ISO 2859-2 (ISO 1985), and then calculates the quality control response, which can be an error, or the standard responses: accepted (Ac) or rejected (Re).

Table 4.34. Results for direct evaluation of point data using Euclidean distance (Xavier et al. 2015c).

LQ (%) Sample size /

Acceptance Tolerance (m)

4 5 5.17 6

5.0 50 / 0 Error Error Error Error

8.0 32 / 0 Re Re Re Re

12.5 32 / 1 Re Re Re Ac

20 20 / 1 Re Re Re Ac

32 20 / 3 Re Ac Ac Ac

The results shown in Table 4.34 indicate that the UNE 148002 service is working in accordance with the procedures described in the standard for point evaluation. We added to the list of tolerances the resulting value for the NSSDA evaluation (5.17 m), which was calculated using other NSSDA service (Section 4.2.1). For the LQ = 5% the service threw error messages indicating that there was an insufficient sample size for this configuration. In this experiment there was two errors greater than five meters, so they prevented the acceptance of the lot in many configurations, like LQ between 8%

and 20% in this tolerance. For the configurations using a sampling size of 20 elements, the service randomly selected the 20 from the 32 given points.

For the line essays we chose an extract with 50 objects of line data in systematic disturbance datasets (see Figure 4.24). For the line assessment we considered the lot size equal to 2000 features.

Figure 4.24. Line datasets for the UNE 148002 service experiment.

In the first essay for line data we considered faulty data those pairs that reach a Hausdorff distance greater than a given tolerance, for a certain LQ. Table 4.35 presents the results for some configurations of LQ and tolerance, which the last one (18.2) is greater than the maximum value. The results indicate that the service is working in conformance with the UNE 148002 procedure. Regarding the sampling size, the service worked in its limit, it used all the 50 available features when possible, and it threw an error message when the user required a more restricted limiting quality.

Table 4.35. Results for direct evaluation of line data using HD (Xavier et al. 2015c).

LQ (%) Sample size / Acceptance

Tolerance (m)

10 15 18.2

8.0 80 / 3 Error Error Error

12.5 50 / 3 Re Re Ac

20 50 / 5 Re Ac Ac

32 50 / 10 Re Ac Ac

The second essay for line assessment used the SBM as the indicative of faulty or valid data. This measure require two parameters: a buffer length that is created around the reference line, and an overlap proportion, that represents the proportion of the test feature's length that is located within the buffer. This combination of parameters (buffer length/overlap proportion) was used as the tolerance. The used tolerances were a combination of three buffer lengths (10, 15, 18 m) with three overlap proportions (99.8, 90, 67%). Table 4.36 shows that the UNE 148002 service worked satisfactorily, so it returned responses according to the standard.

Table 4.36. Results for direct evaluation of line data using SBM (Xavier et al. 2015c).

LQ (%)Sample size / Acceptance

Buffer length (m) / overlap proportion

10 / 0.998 10 / 0.90 10 / 0.67 15 / 0.998 15 / 0.90 15 / 0.67 18 / any

8.0 80 / 3 Error Error Error Error Error Error Error

12.5 50 / 3 Re Re Re Re Ac Ac Ac

20 50 / 5 Re Re Re Ac Ac Ac Ac

32 50 / 10 Re Re Ac Ac Ac Ac Ac

In order to check the flexibility of WPS for output formats, in the UNE 148002 service was implemented two outputs for the execute operation: XML report and PDF report.

The XML report is based on the concepts of the new ISO standards regarding quality evaluation (ISO 19157, ISO 2013) and metadata (ISO 19115-1, ISO 2014). The ISO standard that deals with the XML schema implementation was recently published (ISO/TS 19157-2, ISO 2016). The corresponding XML schemas that can be found at Metadata for Data Quality (MDQ) page (ISO 2015). Based on these schemas, the UNE 148002 service is able to generate an XML report that encodes the quality element assessed (DQ_AbsoluteExternalPositionalAccuracy) as well as some metaquality elements, also described in the draft of Spanish standard. The generated quality report is an XML file that is valid against the XML grammar defined in the MDQ package.

The PDF report is a human-driven report based on the informations generated by the service for the XML report. Despite of the XML report can be read by humans too, as well as by machines, with the PDF report we intend to generate a quality appraisal more suitable for human users, so the UNE 148002 is focused on consumers' needs. Figure 4.25 presents an example of a PDF report generated by the web service.