The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
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for metadata (Figure 3). In continuation is given an overview of
Quality Control on Orthophoto example.
Figure 3. Geoportal in relation with NSDI and Inspire
4. ORTHOPHOTO PRODUCTION
Production of orthophoto is based on Product Specification
(SGA, 2003) which describes all important issues. Some
predecessors are also important to product orthophoto (Scanned
Photos if applicable or digital aerial images, DTM and Aerial
Triangulation) i.e. for correct orthophoto the condition is that
previous products passed on Quality Control. The Figure 4
shows the hole system of products and previous products which
are documented through CRONO GIP.
Figure 4. Products and products' predecessors
The initiate Orthophoto production was based on gray scale
aerial photography and first Product specification described
gray scale orthophoto. The final orthophotos shall have a
radiometric resolution of 8 bits; 256 grey levels. The
distribution of the histogram shall be approximately between 5
(black) to 250 (white). Changes in the product specification are
based on user needs and on new technology methods and
processes. The latest Product specification describe color
product (24 bit colour raster). The delivery consists of delivery
list, production report and data (raster data, vector frame and
toponyms data and orthophoto print). Specification for
Orthophoto Production (SGA, 2003 a) consist od description of
Images used for Orthophoto production, way of Image
rectification, mosaicing, retouch. Also there is described the
way how to collect and represent vector data (toponyms) and
draw map frames. Main parts of Product Specification are also
appendices: Delivery List Requirements, Maps Sheet
Nomenclature, Cartographic Key for Toponyms and Official
gazetteers for public roads and settlements.
The accuracy of final Orthophoto should have standard
deviation of 1 meter (for well defined objects).
5. QUALITY CONTROL SYSTEM
Quality control system is based to fulfill 95% confidence level
for delivered data. The whole QC system includes
documentation (general documents, guidelines for QC and
check list), human recourses and equipment (software,
hardware and professional devices). . General principles are
described in Quality Control Principles of Geographic
Information (CGI, 2004b). General principle of methos are
shown on Figure 5. All the data needed to perform an internal
direct data quality evaluation method is internal to the dataset
being evaluated, e.g. controls by means of software. External
direct quality evaluation requires reference data external to the
dataset being tested, e.g. check against other data.
Figure 5. Quality evaluation methods
QC Process includes determination of quality plan and quality
methods, executing and reporting. Concrete quality plan means
defining dataset, identification quality elements and
subelements and tolerances, control methods, acceptable level
of quality and way of reporting.
The Quality Plan is developed according to definitions of ISO
quality elements, subelements, descriptors, evaluation methods
and selected tolerances (ISO, 2001).
Execution of the Quality Plan on Spatial data results with the
Quality Evaluation Reports with information about dataset,
used quality elements, executed measurements i. e. controls,
tolerances according to specification, used methods - full
control or sampling (CGI 2004c), used equipment or software,
processing of measurements, comparing results with tolerances
and finaly quality evaluation of product delivery (product is
acceptable or not).
Quality elements and subelements used for spatial data quality
control are used according to Product Specification (State
Geodetic Administration) and described in separated document.
The process of quality control procedures can be divided in four
classes depending of the control type used: manual full (MF),
automatic full (AF), manual sample (MS) and automatic sample
(AS).
In praxis the quality control process includes: control of
delivery, execution of control (manual, sampling or automated)
and reporting.