Abstract
The Orthophoto CR is produced in co-operation with the Land Survey Office and the Military Geographical and Hydrometeorological Office. The product serves to ensure a defence of the state, integrated crisis management, civilian tasks in support of the state administration and the local self-government of the Czech Republic as well. It covers the whole area of the Republic and for ensuring its up-to-datedness is reproduced in the biennial period. As the project is countrywide, it keeps the project within the same parameters in urban and rural areas as well. Due to economic reasons it can´t be produced as a true ortophoto because it requires large side and forward overlaps of the aerial photographs and a preparation of the digital surface model instead of the digital terrain model. Use of DTM without some objects of DSM for orthogonalization purposes cause undesirable image deformations in the Orthophoto. There are a few data sets available for forming a suitable elevation model. The principal source should represent DTMs made from data acquired by the airborne laser scanning of the entire area of the Czech Republic that was carried out in the years 2009-2013, the DMR4G in the grid form and the DMR5G in TIN form respectively. It can be replenished by some vector objects (bridges, dams, etc.) taken from the geographic base data of the Czech Republic or obtained by new stereo plotting. It has to be taken into account that the option of applying DSM made from image correlation is also available. The article focuses on the possibilities of DTM supplement for ortogonalization. It looks back to the recent transition from grid to hybrid elevation models, problems that occurred, its solution and getting some practical remarks. Afterwards it assesses the current state and deals with the options for updating the model. Some accuracy analysis are included.
Highlights
Since 2003, every year the Czech Geodetic and Cadastral Office (ČÚZK) announces public a tender for aerial survey photos of one of the three regions (East, Central, West), Czech Republic
Georeferencing has the biggest influence on the absolute orthophoto positional accuracy quality, furthers the parameters of aerial photography and the accuracy of the digital elevation model used for the orthogonalization
We only evaluated objects that didn't surpass deformations or spatial discrepancies larger than 2 pixels (0.5 m in object space)
Summary
Since 2003, every year the Czech Geodetic and Cadastral Office (ČÚZK) announces public a tender for aerial survey photos of one of the three (see Fig 1.) regions (East, Central, West), Czech Republic (from r. 2012 in two zones only). Georeferencing has the biggest influence on the absolute orthophoto positional accuracy quality (selection the number and distribution of control points, calculation of the elements of exterior orientation by the digital automatic aerotriangulation), furthers the parameters of aerial photography and the accuracy of the digital elevation model used for the orthogonalization. All these factors have evolved considerably due to significant changes in 2010. It was necessary to carry out a comprehensive research or survey, resulting in a realistic estimation of the absolute positional accuracy of the “Orthophoto of the CR” created in 2010 and 2011 (for Central and West zones)
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