In the generation of the DTM, objects from the ground were removed. However, there were residual objects on the ground, such as short bridges, small buildings, embankments, etc., that were overlooked and could not be removed by TerraScan. In addition, there were areas on the DTM that didn’t have data, which may be due to ash clouds, turbulence, water bodies 1 , etc. These residual objects should be removed and areas with no data should be filled in to have a good quality DTM. An ArcMap plug-in tool developed by UP-DREAM, called ArcTeam, was used to edit LiDAR digital elevation models (DEM).

 

              The ASCII files were first loaded into ArcMap using the ArcTeam Tool (LoadASCII tool). This also mosaicked the tiles and applied hillshading. It converted the elevation into Orthometric Height using EGM08 Geoid and set the projection to WGS 84 Zone 51. In loading the ASCII files into ArcGIS, a layer named v_no_data_area was created that contains areas where there is no data.

 

fig22             These areas were filled in using the FillDataGaps tool of ArcTeam. In removing residual objects in the DTM, an interpolation procedure carried out by the InterpolateRaster Tool of ArcTeam was performed. An example of an unedited DTM is shown in Figure 22, which portrays a small bridge not removed by TerraScan. In order to have a good DTM appropriate for flood modeling, this small bridge should be removed, otherwise the flood modeling software will interpret this as an obstruction to water flow.

 

fig23

 

         Figure 23 shows the DTM after editing in which the small bridge has been removed. Another issue in the generation of DTM is the existence of flattened hilltops and rice paddies. In the latter case, a hill looks like a plateau and in the latter, a rice paddy appears flat. To restore the appropriate shape of a hill and the embankment of a rice, a secondary DTM (t ASCII) is needed. In the secondary DTM, the embankments are preserved although more vegetation and buildings can be found. It is therefore the appropriate DEM that can be used to restore the missing part of the DTM. This can be done by the ObjectRetrieval Tool of ArcTeam.

                   There are also areas in the DSM that have no data. In editing the DSM (d layer), these areas should also be filled in. This was done by running the CopyFilledData Tool also in ArcTeam. In performing this operation, the 1 st return DSM (s layer) and the edited DTM were used. Figure 26 shows areas of the DSM (Blk47A) that have no data. Figure 27 shows the DSM after the application of the CopyFilledData Tool in the areas that have no data, which are now filled in.

1
2
3
4

 

Figure 2.8 presents the edited LiDAR data coverage for Region 7. The red polygons represent the Negros Oriental flights, the green for Cebu and blue for Bohol.

 

Lastly, the different blocks of DTM and DSM were mosaicked to come up with the DTM and DSM of the whole flight mission. At the time of the writing of this report, all data forwarded to us by UPD-DPC were all edited already. A total of 49 flights has been edited covering Region 7.

 

table21
fig28