The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008
A monochrome shaded point map is a map that the ground
points extracted from the filtering process are overlaid on a
shaded map created from DSM data. Figure 2 shows a
monochrome shaded point map. The ground data to be used are
shown in small red points. The places in dark red area in the
map are the places where the measurement data coincide and
thus have high point density. The shaded map is presented in
monochrome depends on the amount of shadow. And the
ground points are presented in the plainly different color from
the monochrome shaded map. The following are the
advantages of using a monochrome shaded map as the
background:
2.1.1 Easy Viewing of Ground Objects: the shaded map
does not interfere with the display of the point clouds that are
targeted for examination. It allows interpretation of topography
and features.
2.1.2 Data Created from Measurement Data: As it is
created from measured data, it is possible to determine whether
measurements have actually been taken or not.
2.1.3 No Distortion and Halation: there is no distortion or
halation of the buildings that is quite different from the aerial
photograph. Because the monochrome shaded point map is
generated only from the Lidar point clouds.
2.1.4 No Special Equipment for 3D-Recognition: It allows
3D-recognition without special equipment or spectacles.
Figure 2 Monochrome Shaded Point Map
2.2 Disadvantages of a monochrome shaded point map
While the legibility of point clouds after filtering is high, one
disadvantage of a monochrome shaded point map is that it
cannot be used alone. Figure 3 shows a monochrome shaded
point map in a forested area. It is impossible to interpret
whether point clouds displayed on the map represent ground
point data or feature data derived from the measurement of the
tops of trees. Comparison with another QC/QA map is required
to verify whether the feature data of the forest remain on the
map or not. 3
3. DESCRIPTION OF QUALITY CONTROL METHOD
3.1 Outline and Features of Quality Control Method
As mentioned above, in some cases, the interpretation of
monochrome shaded point maps can be problematic, and in
such cases the quality control of the maps may not be
satisfactory. To solve this problem, we developed a new
quality control method using both monochrome shaded point
maps and color-shaded maps. Figure 4 shows the workflow of
the new QC/QA method.
Figure 3. Monochrome Shaded Point Map of a Forested
Area
Figure 4. Workflow of the Quality Control Method
3.2 Examination of the Color-Shaded Map
It is known that a color-shaded map allows the presentation of
micro topology. The filtering results that are examined using
this QC/QA map are shown in Figure 5. The reasons for
choosing the color-shaded map are as follows:
• A color-shaded map is suitable for detailed examination of
forests, which cannot be examined with a monochrome
shaded point map.
• It can be created automatically and is suitable for
processing a large amount of data.
• Feature data remained after filtering have an elevation
different from the surrounding topography, and this
difference creates a shadow on the color-shaded map. This
shadow serves as a reference and provides a clear basis for
decision-making in the examination of the filtering (shown
in Figure 6) .
• It enables examination of detailed and fine feature data.