Lab 6: Topo-bathy Applications

Goals and Background

The main purpose of the lab is provide me with hands-on participation working with topo-bathy lidar. The lab will demonstrate how to perform basic QA/QC, generate and conflate shoreline breaklines, and enforcement of shoreline behavior when generating a topo-bathy lidar Digital Terrain Model (DTM) and hillshade products.

Production of extensive topo-bathy derivatives such as flood models are extremely dependent on high computing power. We do not have access to such computers here, so the products of this lab are just the tip of the iceberg of what can be done with the data.

Methods

Before starting a backup file of the data was created.

QA/QC

I will be using the windows version of LP 360 for the QA/QC portion of the lab.

I first opened the LAS dataset and NAIP imagery in LP360 (Fig. 1). After opening the LAS file and the NAIP imagery I inspected the data for errors made during the classification. The data was provided with the ground, and water classified. Numerous errors were noticed immediately upon inspection. In some areas there were multiple elevations levels classified as ground (Fig. 2). The water classification was classified as Class 31 (reserved) for some unknown reason. The largest issue for our lab purposes was many ground points were left unclassified (Fig. 3).

(Fig. 1) LAS files and NAIP imagery of study area opened in LP360.

(Fig. 2) Ground classification error displayed in the profile window. Note the various elevations of ground classified points.

(Fig. 3) Unclassified ground points displayed in the 3D viewer of LP360. Examine the window on the right and notice all of the gray points (unclassified) intermixed with classified ground points.

A fellow classmate Max came up with a effective plan to add help fill in the unclassified ground points. We utilized a height filter to classified other ground points at the same level (0 elevation) to a minute (.1 elevation) bit higher (Fig. 4).

(Fig. 4) Height filter parameters set in the point cloud task window.

Breakline creation

The next step of the lab was to create breaklines for both the shoreline edge and the land area. I utilized the same methods as Lab 5 to create 2 separate shapefiles (Fig. 5). The created shapefiles will be used in the next step of creating the DTM and the Hillshade. I was able to conflate the shoreline shapefile as I digitized it in the LP360 extension of ArcMap. The land area was not as kind during the digitization process. I ended up digitizing the land area as a 2D shapefile and conflating it in the windows version of LP360 following the same process as Lab 5.

(Fig. 5) Image displaying the shapefiles created for the shoreline and the land area.

Generation of topo-bathy seamless DTM

The final step of the lab was to produce a DTM and Hillshade for the study area. Utilizing the Export Wizard I set the parameters very similar as Lab 5. The parameters were set to the following:

• Export Type: Surface
• Source Points: 2 Ground, 11 Road surface, 31 Reserved (Water Points)
• Surface Method: Triangulation (TIN)
• Cell Edge Length: 2
• Surface Attribute(s) to Export: Elevation and Hillshade
• Export Format: Binary Raster
• Breakline enforcement was set to utilize the 2 shapefiles created with the Elevation set to shape.
• Perform-On-the-Fly Topology Corrections was checked.

Results

(Fig. 6) DTM result displayed in LP360. The extent is zoomed in to see the detail.

(Fig. 6) DTM result displayed in LP360 showing a few errors which resulted.

Discussion

Examining Fig. 6 you can see an error in the DSM. The breaklines which were created should have excluded this area but for some reason it hasn't. Upon close examination there are a few other areas which similar issues. All of these area are outside of the breakline. Further investigation is required to determine the source of the errors.

Sources

LAS, tile index, and metadata for Hiawatha National Forest coastal
area in Delta County, MI are from NOAA Office for Coastal Management. NAIP imagery is from

United States Department of Agriculture Geospatial Data Gateway.