Automatic generation of elevation data over Danish landscape

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Automatic generation of elevation data Table 7.19 shows that it has not been necessary to eliminate very many points in flat terrain. For the landscape types village and hilly terrain, between approx. 1% and approx. 15% have been eliminated. Again, it has been necessary to eliminate large amounts of points for the landscape types gravel pit and woods, where the percentage lies from approx. 25% to approx. 50 %. Resolution 90 15μm 30μm 60μm Mesh size Image scale 1:25,000 Percentage of eliminated points Flat terrain Gravel pit Village Hilly terrain Woods 5 x 5 m 42.2 % 14.8 % 48.0 % 54.7 % 47.2 % 12.5 x 12.5 m 33.7 % 56.5 % 35.2 % 50.0 % 39.4 % 25 x 25 m 21.4 % 54.5 % 24.0 % 39.8 % 39.3 % 5 x 5 m Cannot be calculated! 12.5 x 12.5 m 6.8 % 30.6 % 25.9 % 20.4 % 38.0 % 25 x 25 m 2.8 % 46.5 % 14.7 % 17.2 % 32.3 % 5 x 5 m Cannot be calculated! 12.5 x 12.5 m 2.0 % 21.3 % 8.1 % 7.2 % 36.8 % 25 x 25 m 3.4 % 37.7 % 14.6 % 12.0 % 37.1 % Table 7.20: Percentage of points eliminated by the iteration process for scale 1:25,000 and the landscape types. Table 7.20 shows that for images in scale 1:25,000 and resolution 15μm, it has been necessary to eliminate markedly more points for all landscape types compared to the two other resolutions. Furthermore, the degree of elimination is the same for all landscape types which is not the case for the other scales and resolution. 7.5.4 Summation for the landscape types Tables 7.18 – 7.20 show that gross errors mainly occur in those areas where they are expected. In scales 1:5,000 and 1:15,000, the fewest gross errors are found in the landscape type open, flat terrain which is to be expected, as this area is flat without trees or buildings. In scale 1:25,000 and resolution 15μm, it has been necessary to eliminate markedly more points for all landscape types compared to the two other resolutions. It has not been possible to find an explanation for this phenomenon. In the landscape type open, hilly terrain, quite a few unexpected gross errors occur. The area includes fields, a few hedges, smaller overgrown areas and a couple of farms with vegetation around them. The expectation was that these objects would be eliminated by Match-T. In the landscape types gravel pit and woods, the largest amount of gross errors are eliminated which was to be expected. In the next section a closer look is taken at the causes of gross errors. 7.5.5 Correlation errors or objects in the terrain? The PIL programme gives the option of visualising the deviations between the frame of reference and the generated grid as error arrows. Each landscape type has been assigned a colour. These are: � Flat terrain = green � Gravel pit = yellow/orange � Village = red � Hilly terrain = violet � Woods = blue The error arrows are designed so that negative deviations give a dark downwards pointing arrow, and positive deviations give a light upwards pointing arrow, an example is shown in figure 7.2.
Gravel pit Village Flat terrain Hilly terrain 7 The investigation Village Woods Figure 7.2: The error arrows show the deviation between the frame of reference and the generated grid. Pale colours indicate a positive error, dark colours a negative error. The error arrows are shifted, so that the starting and finishing point for the individual arrows do not adjoin. Figure 7.2 shows that there are few gross errors in the landscape type open, flat terrain and village, whereas there are relatively many unforeseeable gross errors in the landscape type hilly terrain. There are many positive gross errors in the landscape type woods and a few negative ones. By means of the error arrows generated by the analysis programme and an orthophoto, it is possible to make a closer analysis of where the errors are located, and whether it is a question of a correlation error or of objects in the terrain. This visualisation does not shift the error arrows, as their location after the shift will not fit in with the orthophotos. The choice has been to take a closer look at two resolutions of images in scale 1.25,000, namely the results for the resolutions 15μm and 60μm . The choice is based on the fact that large gaps have appeared within each resolution in the number of points eliminated, and furthermore, that these two results differ from the tendency in the other images. Tables 7.18 - 7.20 show that there are many gross errors in the landscape types woods, gravel pit and hilly terrain. The gross errors are symbolised by arrows. The arrows are here scaled up by a factor 20, so that they are easier to find. The result for scale 1:25,000, resolution 15μm and mesh size 25 x 25m is shown in figure 7.3. 91
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Automatic generation of elevation d
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Abstract This thesis consists of tw
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Table of contents: Table of content
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Table of contents: 5.3.2 The post-p
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1 Introduction 1 Introduction The s
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1 Introduction expectation that the
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1 Introduction Today, the Danish na
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� C Description of the PIL progra
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Page 40 and 41: Automatic generation of elevation d
Page 57 and 58: 5 Preparation for the grid generati
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A.1 ABM and FBM level values (edge
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A.1.2.3.2 The Förstner operator A.
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This is done by an adjustment by th
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A.1.2.3.5 Quality evaluation of the
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K 1 A.1 ABM and FBM By means of the
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A.1.4 FBM in one dimension A.1 ABM
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A.1 ABM and FBM Image pyramid Objec
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Appendix B
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B.1 Description of the data materia
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Figure B.1.2: The flight paths for
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B.1 Description of the data materia
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B.2 Data capture B.2 Data capture T
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Figure B.2.3: Example of the rover
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y = 0.011 m z = 0.011 m B.2 Data ca
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B.2 Data capture The accuracy requi
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B.2 Data capture The standard devia
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Appendix C
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C.1 Description of the analysis pro
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C.1.3.3 Calculation options C.1 Des
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� � C.1 Description of the anal
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Editing programme
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Editing programme Input file The in
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Editing programme
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Bundle adjustment 36 8961 56 58 53.
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Bundle adjustment E.2 Fixed bundle
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Bundle adjustment 110 0502 57 0 15.
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Bundle adjustment 575 -234337.117 2
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Bundle adjustment 1106 -236131.840
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Bundle adjustment E.5 Aerotriangula
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Bundle adjustment 990 -232553.563 2
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Bundle adjustment CORD 1013 -234859
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Bundle adjustment A 44 -234597.462
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Bundle adjustment CORD 521 -236301.
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E.6 Aerotriangulation for images in
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Graphic online/offline Graphic onli
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Appendix G: Sizes of grid files G.1
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G.1 Sizes of grid files Appendix H
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Code specification Code specificati
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I.1 Analysis calculations Appendix
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Orthophoto and error arrows
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L.1 STND used as threshold Appendix
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Automatic generation of elevation data over Danish landscape

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