Data Specification on Orthoimagery – Draft ... - INSPIRE - Europa

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INSPIRE Reference: D2.8.II.3_v2.0 TWG-OI <strong>Data</strong> <strong>Specification</strong> on Orthoimagery 2011-06-15 Page 25 As a referencing framework for Pan-European Orthoimagery theme data sets aimed at cross-border purposes, the Grid_ETRS89-GRS80 based on ERTRS89 geodetic coordinates as defined in Annex C is recommended for data provision in order to obtain continuous-seamless data. Real time reprojection is recommended for display through the view services serving these data sets. Annex C also explains the need to establish such a common grid. 7 <strong>Data</strong> quality This chapter includes a description of data quality elements and sub-elements as well as the associated data quality measures (section 7.1). The selected data quality measures should be used to evaluate quality of data sets for a specific data quality element / sub-element. The evaluation can be performed at the level of spatial object, spatial object type, dataset or dataset series. The results of the evaluation are then reported at the spatial object type or dataset level in metadata utilising the same data quality elements and measures (see chapter 8). NOTE The selection of appropriate data quality measures represents the first step towards the harmonisation of documenting data quality. In addition, for some of the data quality elements described in section 7.1, minimum data quality requirements or recommendations may be defined. These are described in the section 1.2. Recommendation 1 If data quality information is required at spatial object level then it should be modelled in the data model as an attribute of a relevant spatial object type. 7.1 <strong>Data</strong> quality elements and measures No data quality elements for quantitative evaluation are defined for this theme. Recommendation 2 To evaluate and report the data quality of data sets related to the spatial data theme Orthoimagery, the elements and measures listed in Table 2 should be used. Table 2 – <strong>Data</strong> quality elements for evaluating and reporting the data quality of data sets related to the spatial data theme Orthoimagery Section <strong>Data</strong> quality element and sub-element 7.1.1 Completeness – Omission 7.1.2 Positional accuracy – Absolute or external accuracy 7.1.1 Completeness – Omission Omission should be documented using the rate of missing items. Name Rate of missing items Alternative name – <strong>Data</strong> quality element Completeness
INSPIRE Reference: D2.8.II.3_v2.0 TWG-OI <strong>Data</strong> <strong>Specification</strong> on Orthoimagery 2011-06-15 Page 26 <strong>Data</strong> quality sub-element Omission <strong>Data</strong> quality basic measure Error rate Definition Number of missing items in the dataset in relation to the number of items that should have been present. Description This data quality measure provides an assessment of the rate of pixels without valid radiometric information in an orthoimage. It should apply on the areas of interest of the orthoimage, where no-data values are not expected (e.g. coastal or international boundaries regions should be excluded). Each data producer has to define specifically what valid radiometric information is for a given orthoimagery product (e.g. are cloud covers of concern?). A visual inspection of the image may be sufficient for the assessment. Evaluation scope spatial object type: OrthoimageCoverage Reporting scope data set Parameter – <strong>Data</strong> quality value type Real, percentage, ratio (example: 0,0189 ; 98,11% ; 11:582) <strong>Data</strong> quality value structure – Source reference – Example – Measure identifier 7 (ISO 19138) 7.1.2 Positional accuracy – Absolute or external accuracy Absolute or external accuracy should be documented using root mean square error of planimetry and/or root mean square error in X or Y. Name Root mean square error of planimetry Alternative name RMSEP <strong>Data</strong> quality element Positional accuracy <strong>Data</strong> quality sub-element Absolute or external accuracy <strong>Data</strong> quality basic measure Not applicable Definition radius of a circle around the given point, in which the true value lies with probability P Evaluation scope Spatial object type: OrthoimageCoverage data set data set series Reporting scope Spatial object type: OrthoimageCoverage data set data set series Description The true values of the observed coordinates X and Y are known as xt and yt. From this the estimator σ = 1 n ∑ n i= 1 [( x mi − x ) t 2 + ( y mi − y ) yields the linear root mean square error of planimetry RMSEP = σ Parameter – <strong>Data</strong> quality value type measure <strong>Data</strong> quality value structure – Source reference – Example – Measure identifier 47 t 2 ]
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Data Specification on Orthoimagery – Draft ... - INSPIRE - Europa

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