KEYWORDS: 3D modeling, LIDAR, Data modeling, 3D image processing, Visualization, 3D image reconstruction, Image visualization, Image processing, Visual process modeling, Human-machine interfaces
A visualization toolbox system with graphical user interfaces (GUIs) was developed for the analysis of LiDAR point cloud data, as a compound object oriented widget application in IDL (Interractive Data Language). The main features in our system include file input and output abilities, data conversion capability from ascii formatted LiDAR point cloud data to LiDAR image data whose pixel value corresponds the altitude measured by LiDAR, visualization of 2D/3D images in various processing steps and automatic reconstruction ability of 3D city model. The performance and advantages of our graphical user interface (GUI) visualization system for LiDAR data are demonstrated.
KEYWORDS: LIDAR, 3D image reconstruction, 3D image processing, 3D modeling, Clouds, Buildings, Data centers, Image processing, Image visualization, 3D acquisition
The demand of 3D city modeling has been increasing in many applications such as urban planing, computer gaming with realistic city environment, car navigation system with showing 3D city map, virtual city tourism inviting future visitors to a virtual city walkthrough and others. We proposed a simple method for reconstructing a 3D urban landscape from airborne LiDAR point cloud data. The automatic reconstruction method of a 3D urban landscape was implemented by the integration of all connected regions, which were extracted and extruded from the altitude mask images. These mask images were generated from the gray scale LiDAR image by the altitude threshold ranges. In this study we demonstrated successfully in the case of Kanazawa city center scene by applying the proposed method to the airborne LiDAR point cloud data.
The accuracy of DEM extraction was analyzed from the view of tie point selection in the stereo ALOS/PRISM images,
using PCI Geomatica software. In the analysis we considered three different parameters in the automatic tie point
selection, namely, 1) the number of tie points, 2) the image correlation coefficient of tie points, and 3) the spatial
resolution of DEM extraction. We found that a better DEM extraction accuracy was possible when we adopted a single
tie point with large image correlation coefficient (around 0.8) and the spatial resolution of 2.5 (m) in the automatic tie
point selection from the stereo PRISM images. In addition, we examined the dependence of the DEM extraction
accuracy on the tie point’s elevation in the manual tie point selection. However, no clear dependence on the tie point’s
elevation was found because of large DEM noises at tie points in the mountain area. Finally, some preliminary analysis
results of DEM extraction accuracy were presented from the stereo QuickBird images.
The importance of having a 3D urban city model is recognized in many applications, such as management offices of risk and disaster, the offices for city planning and developing and others. As an example of urban model, we reconstructed 3D KIT campus manually in this study, by utilizing airborne LiDAR point cloud data. The automatic extraction of building shapes was left in future work.
This study is to make an accuracy assessment of the DEM extracted from a stereo pair of ALOS PRISM images of
Kanazawa area, Japan. First of all, we computed 14 linear coefficient parameters in 3D perspective transformation
(3DPT), using 7 and 9 triangular points whose three dimensional coordinate values were given by Geospatial
Information Authority of Japan. The DLT model characterizes the relationship between two dimensional image
coordinate system and three dimensional object coordinate system. As for the tie point on the stereo pair image, we
selected the GCP set L, the GCP set M, and the GCP set H, consist of 15 triangular points with low elevations
(0m<Z<50m), middle elevations (50m<Z<200m) and high elevations (Z>200m), respectively. The three DEMs were
generated with an aid of the OrthoEngine module (PCI Geomatica Ver. 10.3), by assigning these three GCP sets as the
tie point sets. It is very important to input the correct set of pixel and line coordinate values for the DEM extraction. For
this purpose, the pixel and line coordinate values for the Nadir view image and the Forward View image were calculated
by the DLT with newly computed linear coefficients. The accuracy analysis of the extracted DEMs was examined at
independent 10 Check Points (CPs). We found the most accurate DEM was generated using the GCP set M. The overall
accuracy of the DEM with 2.5m spatial resolution was computed to be RMSE = 5.8m in the vertical direction by
comparing the extracted elevation values with measured values at 10 CPs.
We made the operational sky measurements for two and half years from April 2003 to September 2005, using the sky radiometer and presented the analized results of the aerosol optical properties over Kanazawa area, Japan, namely, the optical thickness τa (500) at the wavelength of 0.5μm and Ångstroem exponent α. The reflectance ratios between the visible and short wave infrared bands were computed for typical ground covers, such as the vegetation, urban, and others (soil and sand), using several image data sets of Terra/MODIS and these sky observation data sets.
The surface reflectance ratios for certain land classes in Japan between the visible and infrared bands were computed using the observed sky radiometer data and several data sets of Terra/MODIS in 2002 and 2003. They were found to be different from those in USA. The values of aerosol optical thickness τa were retrieved from Terra/ASTER and Landsat-7/ETM+ data sets over Japan assuming new surface reflectance ratios. We found a good agreement between the retrieved and observed aerosol optical thickness values at our study site. This study suggested the necessity of further works on local and seasonal variations in surface reflectance ratios.
Aerosols three optical parameters, namely, its optical thickness ta(500) at the wavelength of 500nm, Angstrom exponent a, and real part of refractive index Nr, were retrieved from ADEOS/POLDER data by analyzing the observed directional reflectance and polarization information. In this retrieval we applied the directional R-P(Reflectance-Polarization) algorithm to the POLDERs 865nm band data. This retrieval algorithm was proposed previously in our paper and we extend it in this study. The validation on the retrieved results was made by comparing with the sky observation data. We found that the correlation coefficient between the retrieved and measured values was good (R=0.86) in the aerosol optical thickness, whereas it is poor(R=0.32) in Angstrom exponent. In addition, we presented the monthly averaged distribution maps of aerosol's three optical parameters over the oceans from the Indian Ocean to the western Pacific Ocean during April 1-31, 1997. This study indicated that there are extended aerosol regions with large values of real part of refractive index (Nr>1.5) in April in the tropical zone.
We examined three different methods, namely, Method-I, -II, and -III for retrieving local aerosol's optical parameters over the Japan Sea using the ADEOS/POLDER data by comparing with the validation data. Method-I, and Method-II use parameterized directional reflectance and polarization diagrams in two infrared bands, respectively. On the other hand, Method-III uses parameterized directional polarization- reflectance diagrams in a single infrared band. We found that Method-III gives the best agreement with the measured sky validation data. We also presented retrieved distribution maps for the aerosol optical thickness, and Angstrom exponent by Method-III and some discussions on further improvement for Method-III were given.
KEYWORDS: Data compression, Prisms, Image compression, Quantization, Atmospheric modeling, Sensors, Monte Carlo methods, Point spread functions, Radiometry, Atmospheric particles
Advanced visible and near infrared radiometer type 2(AVNIR- 2) is a high resolution land observation sensor, which will be loaded on ALOS. AVNIR-2 is composed of a multispectral and panchromatic subsystem. THese former subsystem is recently named as AVNIR-2; same with the old instrument name. The latter subsystem is named PRISM. The multispectral subsystem has ground resolution of 10m and four spectral bands which have same spectral range with that of AVNIR loaded on ADEOS. PRISM has three line detectors and characteristics of B/H equals 1.0 and ground resolution of 2.5m. By means of these characteristics, topographic maps with contour of 5m elevation interval are planned to be produced from those panchromatic data. Because observing data rate of PRISM is very high, on-board lossy data compression will be applied in order to reduce down link data rate. In this report, influences of the on-board lossy compression for terrain elevation measurements are evaluated. As the results, it is clear that: (1) measurement error of terrain elevation does not increase by on-board lossy data compression, (2) measurement error of terrain elevation decreases by on-board lossy data compression under the condition of turbid atmosphere and (3) measurement error of terrain elevation decreases in spite of atmospheric conditions when block coding is used as a lossy compression method.
An inference of landslide areas using digital elevation data and Landsat TM band 6 data has been performed on the basis of the assumption that the occurrence of landslides is closely related to the amount of underground-water and the topographic features of watersheds. It is shown that it is possible to distinguish between dangerous landslide areas and non-landslide areas by using spatial features of watersheds, such as the area, mean slop and shape factor, and the ground surface temperature obtained from Landsat TM data.
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