Time filter

Source Type

Zhu L.,Finnish Geospatial Research Institute FGI | Lehtomaki M.,Finnish Geospatial Research Institute FGI | Hyyppa J.,Finnish Geospatial Research Institute FGI | Puttonen E.,Finnish Geospatial Research Institute FGI | And 2 more authors.
Remote Sensing | Year: 2015

Open geospatial data sources provide opportunities for low cost 3D scene reconstruction. In this study, based on a sparse airborne laser scanning (ALS) point cloud (0.8 points/m2) obtained from open source databases, a building reconstruction pipeline for CAD building models was developed. The pipeline includes voxel-based roof patch segmentation, extraction of the key-points representing the roof patch outline, step edge identification and adjustment, and CAD building model generation. The advantages of our method lie in generating CAD building models without the step of enforcing the edges to be parallel or building regularization. Furthermore, although it has been challenging to use sparse datasets for 3D building reconstruction, our result demonstrates the great potential in such applications. In this paper, we also investigated the applicability of open geospatial datasets for 3D road detection and reconstruction. Road central lines were acquired from an open source 2D topographic database. ALS data were utilized to obtain the height and width of the road. A constrained search method (CSM) was developed for road width detection. The CSM method was conducted by splitting a given road into patches according to height and direction criteria. The road edges were detected patch by patch. The road width was determined by the average distance from the edge points to the central line. As a result, 3D roads were reconstructed from ALS and a topographic database. © 2015 by the authors.

Hakala P.,University of Turku | Muhli P.,National Land Survey of Finland | Charles P.,University of Southampton | Charles P.,University of Cape Town
Monthly Notices of the Royal Astronomical Society | Year: 2014

We report the results of quasi-simultaneous optical and near-IR (NIR) photometry of the lowmass X-ray binary, 4U 1957+115. Our observations cover the B, V, R, I, J, H and K-bands and additional time series NIR photometry. We measure a spectral energy distribution (SED), which can be modelled using a standard multitemperature accretion disc, where the disc temperature and radius follow a power-law relation. Standard accretion disc theory predicts the power-law exponent to be -3/4, and this yields, perhaps surprisingly, acceptable fits to our SED. Given that the source is a persistent X-ray source, it is however likely that the accretion disc temperature distribution is produced by X-ray heating, regardless of its radial dependence. Furthermore, we find no evidence for any emission from the secondary star at any wavelength. However, adding a secondary component to our model allows us to derive a 99 per cent lower limit of 14 or 15 kpc based on Monte Carlo simulations and using either an evolved K2 or G2V secondary star, respectively. In >60 per cent of cases, the distance is >80 kpc. Such large distances favour models with a massive (>15 M) black hole primary. Our quasi-simultaneous J-and V-band time series photometry, together with the SED, reveals that the optical/NIR emission must originate in the same region, i.e. the accretion disc. The likely extreme mass ratio supports suggestions that the accretion disc must be precessing which, depending on the length of the precession period, could play a major part in explaining the variety of optical light-curve shapes obtained over the last two decades. © 2014 The Authors.

Somero A.,University of Turku | Hakala P.,University of Turku | Muhli P.,National Land Survey of Finland | Charles P.,University of Southampton | And 3 more authors.
Astronomy and Astrophysics | Year: 2012

Context. X1822-371 is the prototypical accretion disc corona X-ray source, a low-mass X-ray binary viewed at very high inclination, thereby allowing the disc structure and extended disc coronal regions to be visible. As the brightest (closest) such source, X1822-371 is ideal for studying the shape and edge structure of an accretion disc, and comparing with detailed models. Aims. We study the structure of the accretion disc in X1822-371 by modelling the phase-resolved spectra both in optical and X-ray regime. Methods. We analyse high time resolution optical ESO/VLT spectra of X1822-371 to study the variability in the emission line profiles. In addition, we use data from XMM-Newton space observatory to study phase-resolved as well as high resolution X-ray spectra. We apply the Doppler tomography technique to reconstruct a map of the optical emission distribution in the system. We fit multi-component models to the X-ray spectra. Results. We find that our results from both the optical and X-ray analysis can be explained with a model where the accretion disc has a thick rim in the region where the accretion stream impacts the disc. The behaviour of the Hβ line complex implies that some of the accreting matter creates an outburst around the accretion stream impact location and that the resulting outflow of matter moves both away from the accretion disc and towards the centre of the disc. Such behaviour can be explained by an almost isotropic outflow of matter from the accretion stream impact region. The optical emission lines of He II λ4686 and 5411 show double peaked profiles, typical for an accretion disc at high inclination. However, their velocities are slower than expected for an accretion disc in a system like X1822-371. This, combined with the fact that the He II emission lines do not get eclipsed during the partial eclipse in the continuum, suggests that the line emission does not originate in the orbital plane and is more likely to come from above the accretion disc, for example the accretion disc wind. © 2012 ESO.

Hakala P.J.,University of Turku | Charles P.A.,South African Astronomical Observatory SAAO | Muhli P.,National Land Survey of Finland
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present results from several years of fast optical photometry of 4U0614+091 (V1055 Orionis), a candidate ultracompact X-ray binary most likely consisting of a neutron star and a degenerate secondary. We find evidence for strong accretion-driven variability at all epochs, which manifests itself as red noise. This flickering produces transient peaks in the observed power spectrum in the 15-65min period range. Only in one of our 12 optical data sets can we see evidence for a period that cannot be reproduced using the red noise model. This period of 51min coincides with the strongest period detected by Shahbaz et al. and can thus be taken as the prime candidate for the orbital period of the system. Furthermore, we find some tentative evidence for the X-ray versus optical flux anticorrelation discovered by Machin et al. using our data together with the all-sky X-ray monitoring data from RXTE/All Sky Monitor. We propose that the complex time series behaviour of 4U0614+09 is a result of drastic changes in the accretion disc geometry/structure on time-scales from hours to days. Finally, we want to draw attention to the interpretation of moderately strong peaks in the power spectra of especially accreting sources. Many of such 'periods' can probably be attributed to the presence of red noise (i.e. correlated events) in the data. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Dahlqvist S.,National Land Survey of Finland | Ronnholm P.,Aalto University | Salo P.,Aalto University | Vermeer M.,Aalto University
Remote Sensing | Year: 2011

In this study, we describe a system in which a GPS receiver mounted on the roof of a car is used to provide reference information to evaluate the elevation accuracy and georeferencing of airborne laser scanning (ALS) point clouds. The concept was evaluated in the Klaukkala test area where a number of roads were traversed to collect real-time kinematic data. Two test cases were evaluated, including one case using the real-time kinematic (RTK) method with a dedicated GPS base station at a known benchmark in the area and another case using the GNSSnet virtual reference station service (VRS). The utility of both GPS methods was confirmed. When all test data were included, the mean difference between ALS data and GPS-based observations was -2.4 cm for both RTK and VRS GPS cases. The corresponding dispersions were ±4.5 cm and ±5.9 cm, respectively. In addition, our examination did not reveal the presence of any significant rotation between ALS and GPS data. © 2011 by the authors.

Kolis K.,Aalto University | Hiironen J.,Aalto University | Arola E.,National Land Survey of Finland | Vitikainen A.,Aalto University
Silva Fennica | Year: 2014

Buyers of standing timber take not only the market situation but also the harvest costs into consideration when making purchase offers. In Finland, 85% of all timber is sold as standing timber, but there is little information for forest owners and third parties regarding how differences in harvest costs are reflected in the stumpage prices. This article analyses the relationship between salespecific factors and stumpage prices in Finland. Data on 4824 standing timber sales between 2008 and 2012 were gathered from five local Forest Management Associations. Regression analyses were run on the stumpage prices (euros m–3) paid for sawlogs and pulpwood. Seasonal harvest restrictions, the volume of the sale and the timber assortment influenced stumpage prices, as did the presence of forest damages. Prices also differed over time and between locations. Furthermore, the forest haulage distance was statistically significant for pulpwood. The results suggest that the size of the individual sales and the composition of assortments affect the income owners earn from their forest. The results can be used to estimate stumpage prices and the monetary impacts on forest owners of procedures such as forest road network planning and land consolidation, as well as for valuation of forests. © 2014, Finnish Society of Forest Science. All rights reserved.

Honkavaara E.,Finnish Geodetic Institute | Nurminen K.,Finnish Geodetic Institute | Markelin L.,Finnish Geodetic Institute | Suomalainen J.,Finnish Geodetic Institute | Ilves R.,National Land Survey of Finland
Photogrammetric Record | Year: 2011

Novel photogrammetric sensors open up new possibilities for measuring the radiometric and geometric properties of the earth's surface. To ensure optimal use of these complex, rapidly developing, diverse systems, it is becoming crucial to have a means of calibrating and validating complete imaging systems, and even production lines, in operational conditions. This paper presents a calibration and validation methodology based on a permanent test site (Sjökulla) and demonstrates its use in a calibration and validation campaign for a large-format photogrammetric imaging system, the Intergraph DMC. The major objective of the campaign was to perform acceptance testing of the new camera system procured by the National Land Survey of Finland. The evaluation proved the high geometric and radiometric performance of the imaging system and demonstrated the potential of spectrodirectional photogrammetric 3D imaging. The usability aspects of test site calibration and validation from the point of view of a mapping organisation were also considered.© 2011 The Authors. The Photogrammetric Record © 2011 The Remote Sensing and Photogrammetry Society and Blackwell Publishing Ltd.

Jakobsson A.,National Land Survey of Finland | Ilves R.,National Land Survey of Finland
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2016

The National Land Survey (NLS) has had a digital topographic database (TDB) since 1992. Many of its features are based on the Basic Map created by M. Kajamaa in 1947, mapping first completed in 1977. The basis for the renewal of the TDB begun by investigating the value of the TDB, a study made by the Aalto University in 2014 and a study on the new TDB system 2030 published by the Ministry of Agriculture in 2015. As a result of these studies the NLS set up a programme for creating a new National Topographic Database (NTDB) in beginning of 2015. First new version should be available in 2019. The new NTDB has following key features: 1) it is based on processes where data is naturally maintained, 2) it is quality managed, 3) it has persistent Ids, 4) it supports 3D, 4D, 5) it is based on standards. The technical architecture is based on interoperable modules. A website for following the development of the NTDB can be accessed for more information: kmtk.maanmittauslaitos.fi.

Loading National Land Survey of Finland collaborators
Loading National Land Survey of Finland collaborators