Lab 5: Breakline Creation, Conflation, and Enforcement

Background and Goals:

This lab focused on the process of creating and enforcing hard breaklines for the production of LIDAR derivatives. The lab covered the creation, identification, and fixing of potential topological errors in breaklines. It then worked through the process of conflation of those breaklines and configuring the enforcement of the breaklines for production of the derivative and the production of those derivatives: contours and digital terrain models (DTMs). This lab used both LAS and breakline data from both Eau Claire and Lake County, IL datasets. 

Methods:

     Part 1: Breakline QA/QC and elevation conflation

          Section 1:

This section utilized optical imagery to perform QA/QC on soft breaklines. Imagery was brought into ArcMap and breaklines were properly configured so that islands were digitized as holes in polygon shapes. This was performed with the Illinois dataset.

Figure 1: Islands incorrectly digitized

          Section 2: Z conflation of breaklines for ponds and lakes

After displaying the Illinois LAS dataset by TIN surface, the breaklines were brought in that were corrected in the previous section. A new conflation task was created for the conflation of these breaklines, and later for the breaklines of the Eau Claire dataset (although with different settings). The shapefile breaklines were conflated using ground and water points for source points. For the ponds and lakes the summarize Z method using create flat 3D feature was used and assigning the same Z to each vertex was turned on. Z values within 5 map units were used to create z values for the shapefile and points were not classified within closed lines. Pure drape was used for islands and points were classified within closed lines. Rivers were conflated with the same method as islands. The conflation process was now run.

          Section 3: Z conflation of breaklines for wide rivers

For the city of Eau Claire imagery, riverbanks were digitized. The LAS dataset was brought in to ArcMap and the dataset was filtered so that only ground and water classified features were shown. A breakline polygon was then digitized around the riverbank so that the breakline always fell over ground points that were very close to the water, or over water at the end of the data coverage for the river. This made certain that Z values were included for every vertex in conflation. In creating the shapefile, Z and M values were turned on so that they could later be conflated. The shapefile was later brought into LP360 to be conflated. The vertical and horizontal coordinate systems that were used with the imagery and LAS layers were used for this shapefile. Conflation was performed in LP360 using the drape method and a 5 unit window.

The centerline was next digitized similarly, and then also conflated in the standalone LP360 application with similar parameters.

     Part 2: Breakline enforcement

          Section 1: Hydro-flattening of ponds and lakes

This section involved using the 3D conflated breaklines created in the previous section for Lake County, IL to flatten ponds and lakes within the study area. Breakline enforcement was turned on before it was run to see how the result may look. On the fly topology correction was toggled on and off to see the areas where topology may need to be edited. Contours were also enabled so that the results of a DTM could be seen before the DTM was actually executed. 

The DTM surface model was created using the export lidar data button. Elevation and hillshade options were used and the data was exported as a binary raster. Breaklines were enforced with water used as the buffer class. The process was run.

          Section 2: Extraction of contours

This process used a similar export process as the last section to export contours (options next to elevation and hillshade). This option opened up a new tab with options for the contours that would be generated. The options used are below:

• Contour File Type: Shapefile. 
• Check Export as 3D Shapes checkbox. 
• Contour Interval: 15 
• Shortest Contour: 150 
• Index Type Code: 1 
• Intermediate Type Code: 2
• Check Smooth Corners
• Vertex Spacing: 6

After these were set the annotation tab settings were set as below:

• Export Annotation: Check. 
• Posting Frequency: 900
• Shortest Contour to Annotate: 33 
• Text height: 20 
• Annotation Type Code: 3
• Export Intermediate Annotation: Unchecked
• Export Extent: Draw Window in Map

          Section 3: River hydro-flattening and downstream constraint

 In this section the Chippewa River in Eau Claire was hydro-flattened, then the DTM was exported from the data similar to how the Illinois lakes and ponds were hydro-flattened. 

     Results: 

Breakline Conflation resulted in Z values being propagated at vertices.

Figure 2: Z values after river hydro-flattening and conflation

DTMs were created for each dataset:

Figure 3: Eau Claire DTM export

Figure 4: Eau Claire Hillshade Export

In the Eau Claire exports it is apparent that some areas were not hydro-flattened. This is especially apparent on the right arm coming off the Chippewa River that is the Eau Claire River. This area was not digitized along with the Chippewa river, and thus was not corrected. Also, in certain areas of the Chippewa River there are apparent mistakes as well. This may be from poor ground classification along the river bank, or from poor digitization of the bank polygon. These problems could be corrected with further editing and processing but could not be completed due to time constraint. 

Figure 5: Lake County DTM

Figure 6: Lake County Hillshade

Sources:

• Lab instruction from Dr. Cyril Wilson
• LAS data was sourced from Lake County on the Illinois Geospatial Data Clearinghouse 
• NAIP imagery is from the USDA Geospatial Data Gateway.
• LAS data for portion of the Chippewa Valley is from The City of Eau Claire, WI.