Lab 6: Topo-bathy processing

Goals and Introduction:

The goal of this lab was to work with topo-bathy LiDAR data to gain general skills. The skills practiced were performing basic QA/QC of topo-bathy LiDAR, generating and conflating shoreline breaklines specially tailored to the topo-bathy LiDAR, and configuring the enforcement of the shoreline behavior for creation of derivatives. A DTM and a hillshade raster file were created. The dataset practiced with was located in the Hiawatha National Forest in Delta County, MI.

Methods:

Part 1: QA/QC of topo-bathy point cloud classification

The NAIP imagery and point cloud data supplied for the lab was examined for inaccurate classification using the profile and 3D windows in LP360's standalone Windows application. Using the QA/QC tool, a feature class was created with features that covered areas that needed to be fixed throughout the LiDAR dataset. Theses areas were then visited and corrected. Many points were classified as ground that should have been classified as bathymetric points. Also, many point that were classified as ground, but should have just been left as unclassified, because they fell on buildings and buildings had not yet been classified. The most important area for fixing was the area along the shoreline, where many points that could have been classified as ground were left unclassified. In these areas the manual classification tool in the profile window was used to add ground points (Figure 1) as these point were important for later breakline conflation.

Figure 1 shows the reclassification using the 3D view and the profile. The arrow on the map shows the angle from which the 3D view is being viewed. The profile view shows the Classify Points Below Line tool being used to classify points shown in the cross sectional profile at the bottom of the screen. On the map, the solid white extent of the profile rectangle shows the area that will be classified.

Figure 1

Part 2: Breakline creation for shoreline

Two types of breaklines were created and then conflated in this part of the lab. One breakline (polyline) demarcated the shoreline, and the second breakline (polygon) delineated the non-submerged ground.

Section 1: Shoreline polyline breakline creation

In ArcMap, a polyline shapefile was created with the Z and M vertex information enabled. A field was created for watertype that would later be used for breakline enforcement. The breakline was digitized over the ground points just inland on the shore enough to fall over ground points which were displayed behind the feature. This feature was then brought into the standalone LP360 application for conflation. Conflation was run using the drape method with vertices created every 5 map units, drawing from the ground class.

Section 2: Unsubmerged ground conflation

This process followed the same procedures as above besides for the fact that the shapefile created and conflated was a polygon which encompassed the entire dataset. See Figure 2 below.

Figure 2

Part 3: Generation of the seamless topo-bathy DTM

This part was executed using the Export Lidar Data function. A TIN-method surface was exported to a binary raster elevation model and hillshade layer using the watertype field in both of the breakline features for the breakline enforcement.

Results:

The final results of this lab are the DTM and hillshade rasters seen below. The DTM created was at a fairly fine spatial resolution, offering a useful output which could be used in conjunction with the DTM to offer more insight in display and analysis with these outputs.

Figure 3: DTM

Figure 4: DTM showing detail at a further zoomed in level

Figure 5: Hillshade raster image for overlay

Sources:

• LAS, tile index, and metadata for the Hiawatha National Forest coastal area in Delta County, MI are from the NOAA Office for Coastal Management.
• NAIP imagery was sourced from the USDA Geospatial Data Gateway