Vpliv kakovosti vhodnih podatkov na kakovost ortofota : Influence of Input Data Quality on the Quality of Orthophoto

In the article, the influence of input data for orthophoto map production on the final product is discussed. The quality of orthophoto is mostly influenced by image orientation parameters, quality of the digital elevation model and digital image quality. A short description of orthophoto production procedure is given, and the input data and their impact on the product is treated in more detail. The undestanding of this topic is highly relevant for a correct use of the orthophoto

Theoretical Lidar Point Density for Topographic Mapping in the Largest Scales

When ordering LiDAR data, LiDAR point density per surface unit is important information with decisive influence on the price of the LiDAR survey. The paper first deals with the theoretical calculation of the minimum LiDAR point density, necessary for the acquisition of topographic data of the largest scales. For this purpose the sampling theorem is used. However, since topographic objects (roads, water bodies, etc.) and phenomena represented on topographic maps and in topographic bases are in many cases located under vegetation, also the rate of laser beam penetration through vegetation for the area where the topographic data are to be gathered has to be known. In a research on a test case conducted in the area of the town Nova Gorica we calculated the rate of laser beam penetration for four different vegetation types: scarce Mediterranean vegetation, thick thermophilic deciduous forest, mixed vegetation (meadows, orchards and forest) and built-up area. By connecting the theoretic minimum LiDAR point density with the rate of penetration, we defined the minimum LiDAR point density for the needs of data acquisition on topographic maps of the largest scales or in topographic bases of comparable detail (from 1 : 1000 to 1 : 10,000)

Automatic extraction and building change detection from digital surface model and multispectral orthophoto

The update of topographic databases is an important task fir organizations that maintain them. Building data are one of the important data types in topographic databases. The article describes a method for automatic building extraction from digital surface model and multispectral orthophoto and the use of extraction results for the building change detection in the topographic database. The initial building mask was created from the normalized digital surface model (nDSM). Vegetation was eliminated from the building mask using a modified vegetation index calculated from the infrared orthophoto and also considering the shadow index and the nDMP texture. The final building mask was vectorised using Radon transform, The results of the automatic building extraction were compared to the building cadastre and the actual situation on the ground. The automatic method detected 94.4% of all buildings in the area. We concluded that the described method is appropriate for capturing of the building data for the topographic database in scales 1: 10 000 and smaller. Automatic change detection results (completeness 93.5% and correctness 78.4%) indicate that the described method is appropriate for building change detection

Extraction of power lines from airborne and terrestrial laser scanning data using the hough transform

n this article, a method for the automatic detection of power \ud lines in a horizontal xy plane from airborne and terrestrial \ud laser scanning data is presented. The workflow is composed \ud of four main steps: pre-processing with classification of a \ud point cloud, filtering of the point cloud, the detection of \ud points on the power lines by applying the Hough transform \ud (HT), and vectorisation of power line locations and their \ud intersections. In the pre-processing step, most of the points \ud that are not representing power lines are eliminated via \ud classification of the point cloud. We present our filter, which \ud reduces the number of points in the point cloud further and \ud thus accelerates data processing and increases the reliability \ud of processing in the next steps. We detect the points on the \ud power lines with the HT on the vector points in the xy \ud plane. The final track of the power lines is derived from the \ud straight segments computed by the method of the least squares \ud from the points that HT recognised on the power lines. The \ud results are assessed visually and via relative comparison of \ud the computed intersections coordinates with the reference \ud data manually extracted from the filtered point cloud. The \ud proposed method detects almost all power lines in the test \ud area for both data set

Quality analysis of the sphere parameters determination in terrestrial laser scanning

A point cloud is the result of laser scanning; in the case of\ud terrestrial laser scanning, the point cloud is composed of points\ud scanned from one or more positions. To register these points\ud into one point cloud, so-called tie points are needed; these\ud may be object points (natural targets) or selected stabilized\ud targets (artificial targets). Spherical targets are often used as\ud artificial targets; these must have their centre coordinates and\ud radius determined. The centre coordinates of a sphere are\ud calculated on the basis of scanned points on the spheres’ surface.\ud This paper presents two procedures for determining the best\ud reflection region on the sphere to determine its parameters, and\ud the procedure for determining the optimal distance between\ud the scanner and sphere.The best reflection area on the sphere\ud is determined in two ways. The first is based on minimizing\ud the difference between sphere radii when, in the adjustment\ud process, the radius of the sphere is treated as a known and\ud unknown quantity. The second is based on the standard\ud deviation of the sphere’s centre coordinates at the independent\ud determinations of sphere parameters from randomly chosen\ud scanned points on the sphere surface. For each of the spheres,\ud the best ratio between the laser beam footprint area and the\ud target surface area is calculated for the optimal combination\ud of scanning distance and region. For the best combination\ud of scanning distance and region, we chose the one with the\ud smallest standard deviation of the sphere centre coordinates

Research on the use of orthophoto (DOF5) in practice

Results of the research on the use of orthophoto (DOF5)\ud are represented, obtained by questionnaires that were\ud sent to registered buyers of orthophoto in Slovenia at\ud the end of 2005. The aim of the research was to find\ud out, how often and for what purposes the orthophoto\ud is being used, and especially, what is the opinion of\ud the users about its quality and applicability for their\ud work. As much as 96 % of the questioned population\ud estimated the general quality of orthophoto with regard\ud to their needs as »very good«. The investigation has\ud shown also some deficiency of the product and a wish\ud of the users for a new product of larger scale. The\ud knowlege on the product was tested in the questionnaire\ud as well and the results have shown that not all users\ud have been informed sufficiently on the features of the\ud product, thus additional education and/or information\ud on this would be advantageous

Geometrični popravki optičnih satelitskih posnetkov

The monograph presents a fully automated procedure for geometric correction of optical satellite images, without any manual intervention during the processing. The resulting orthorectified image is in the national coordinate system and constitutes a suitable source for spatial analyses. In the monograph the original procedure connects several different methods into a single, robust system for automatic generation of orthoimages is documented in detail. The work describes the whole automatic orthorectification process, which comprises four basic modules: a module for extracting and preparing the metadata, a module for automatic extraction of ground control points, a module for calculation of parameters of the geometric model, and a module for orthorectification. The experiments and results with RapidEye and WorldView-2 images are also presented. The experiments evaluate the procedure for automatic extraction of points, the geometric model, the elimination of gross errors, and the positional accuracy of the orthoimages. The analisys of the results indicate that the automated procedure produces orthoimages with a positional accuracy of about two pixels or better, even if several gross errors are present among the automatically extracted ground control points.V knjigi je opisan popolnoma samodejen postopek geometričnih popravkov optičnih satelitskih posnetkov, ki deluje brez posredovanja operaterja med obdelavo. Dobljeni ortorektificiran posnetek je v državnem koordinatnem sistemu in predstavlja primerno podlago za prostorske analize. V knjigi je detajlno dokumentiran izviren postopek, ki povezuje več različnih metod v enoten in robusten sistem za samodejno izdelavo satelitskega ortofota. Opisan je celoten postopek samodejne ortorektifikacije, ki ga sestavljajo štirje osnovni moduli: modul za branje in pripravo metapodatkov, modul za samodejno določanje oslonilnih točk, modul za izračun parametrov geometričnega modela in modul za izvedbo ortorektifikacije. Poleg modulov so predstavljeni tudi poskusi s posnetki RapidEye in WorldView-2. Opravljeni poskusi so omogočili ovrednotenje delovanja samodejnega postopka določanja točk, geometričnega modela, izločanja grobih napak in oceno položajne točnosti ortoposnetkov. Analiza rezultatov testov kaže, da lahko samodejni postopek izdela ortoposnetke s položajno točnostjo okrog dveh pikslov ali manj, tudi če je med samodejno določenimi oslonilnimi točkami prisotnih več grobih napak

What about topography? Status and quality of topographic data in Slovenia

Topographic data, an important part of the National Spatial Data Infrastructure, have been given serious attention since Slovenia's independence. It has become publicly available, updated and harmonised. Financing of topographic data in Slovenia has significantly decreased over the previous decade. As a result, the present status is far from acceptable or expected. The current status of the topographic data, as well as its quality and usability for potential users is discussed in this article. The overview starts with basic source data, aerial surveys, photographs and orthophotos. The quality of orthophotos largely depends on the DTM quality. Topographic data is nowadays organised in thematic datasets (geographical names, building cadastre, etc.) or joined in datasets of different levels of accuracy and details. The status in Slovenia is compared to those in some neighbouring and other comparable countries