Lab 5: Breakline Creation Conflation & Enforcement

Goals and Background

The purpose of the lab is to provide me with the hands-on skills required to create and enforce hard breaklines in Lidar data to produce high quality derivatives for various applications. During this lab I will create my own breaklines and examine them for topological issues. I will also be conflating breaklines while inspecting the integrity of the breakline elevation. The final step of the lab will have to enforcing the breakline constraints while also creating a digital terrain model (DTM) along with contours.

Methods

QA/QC of breaklines

I started this lab by performing QA/QC on the breaklines used in Lab 1 to classify the water. I opened the breaklines in LP360 with the NAIP imagery and inspected all of the breaklines, There was a few location issues but since the classification had been complete already I was instructed to not correct the issues. (Fig. 1)

(Fig. 1) Image displaying breakline error. You can see the breakline (blue polygon feature) extends to the road surface.

Conflation of breaklines

The created breaklines I was provided did not have a Z value (elevation) applied. Conflation determines the Z value for the breakline features. I opened the LAS, NAIP, and breakline files from the previous labs in LP360. I created a new Point Cloud Task. The task type was set to Conflation. The Tool Geometry  was set to SHP Layer and the input was the breakline shapefile from the previous labs. Source points were set to Ground and Water. Data Types had the following settings: Fields were set to WaterType (a field in the attributes of the shapefile of the breaklines),

First I set parameters for Pond or Lake and the Conflation Method was set to Summarize Z. I summarized the z values by computing one or more Z values for the input geometry as a whole. I selected Mean Z, Minimum Z, and Maximum Z. A distance of 5.0 map units was set to compute Z values. I unchecked Classify Points within Clased Lines.

Second I set the parameters for Island. The Conflation method was set to Drape and the descriptions was set to Pure Drape. Again I unchecked Classify Points within Closed Lines.

Third I set the parameters for River. I set the parameters exactly the same as I did for Island.

(Fig. 2) Point cloud task window displaying the parameter for the conflation of the ponds, lakes, rivers, island.

I executed the task the point cloud task which created a new shapefile with the Z values applied.

Z conflation of breaklines for wide rivers.

The following section was performed in the LP360 Extension for ArcMap.

Creating two separate shapefiles was the first step in this section of the lab. One shapefile was for the riverbank outline and the second was for the centerline of the river. Next, I started and editing session in ArcMap and created two Custom Conflation Tasks through the Conflate Task Manager on the Digitized Breaklines tool bar. The conflation method for the river centerline was set to Downstream Constraint to make sure the river decreased as it went downstream. The conflation method for the river outline was set to Drape. Digitizing the outline of the river was the next task. I had to make sure I was close to the river edge but not in the water. I was able to active the profile window and display by classification to make sure I was selecting the ground points. I then digitized the river centerline after I completed the outline. After I was completed I examine the shape of the digitization at the full extent of the viewer. (Fig. 3)

(Fig. 3) Image displaying the digitized outline and centerline of the river.

Hydro-flattening of pond and lakes

This section of the lab had me applying the conflated features to hydro-flatten the water features in the study area from the first 4 labs.

This section of the lab was performed in LP360.

After clicking the Export Lidar Data command I set the following parameters in Step 1.

• Export type: Surface
• Source Points: 2 Ground
• Surface Method: Triangulation (TIN)
• Cell Edge Length 3
• Surface Attributes to Export: Elevation and Hillshade
• Export format: Binary Raster

Within the Breakline Enforcement window I set the following parameters:

• Check Use Breakline Enforcement box
• Type Field: WaterType
• Set Island, Ponds or Lakes, and River Elevation field to Shape
• Checked the box to Perform-On-the-Fly Topology Corrections
• Set Buffer Classes: 9 Water

I created a file name and generated the DTM image.

Extraction of contours

The next set of the lab was to create contours for a section of the study area from the first 4 labs. Creating contours for the entire study area was computationally demanding so we only did a small area.

Opening the Export Wizard again I set the same parameters in the first window as the Hydro-flattening section. I selected Contours from the Surface Attributes to Export instead of Elevation and Hillshade like the previous export. Once Contours was check I selected the Contour Tab and set the parameters as displayed in Fig. 4 in the General tab. The parameters I used in the Annotation tab are displayed in Fig. 5. In Step 2 I selected Draw Window in Map and used the Draw Window Tool to select an area to generate the contours in. 

(Fig. 4) General tab parameters under the Contour tab in the Export Wizard.

(Fig. 5) Annotation tab parameters under the Contour tab in the Export Wizard.

River hydro-flattening and downstream constraint

The following methods were performed in the LP360 Extension for ArcMap.

The purpose of this section is to use the river shapefiles created in the previous segment to hydro-flatten the river feature.

The process was the same as hydro-flattening the ponds and lakes. Using the Export Wizard I set the parameters the same way but utilized the conflated shapefiles I created.

Results

(Fig. 6) Display of properly hydro-flattened lake in the DTM/Hillshade combination.

(Fig. 7) Display of a lake which was not correctly hydro-flattened due to in correct island digitization and/or labeling.

(Fig. 8) Display of a portion of the hydro-flattened river in the DTM/Hillshade file.

Discussion

In Fig. 7 and Fig. 8 you can see some imperfections in the results. The errors displayed in Fig. 7 are the result of an island in the middle of the water feature. The islands have to be correctly digitized and labeled for an effective hydro-flattened image. The way it is displayed the program is trying to flatten the island instead of excluding it. In Fig. 8 you can see some horizontal lines on the river. After talking with my professor the cause of this is related to my digitization. When I digitized the shoreline of the river I selected areas to high on the river bank which have a higher elevation causing errors in the hydro-flattening. You can see in the point-bar side of the river the hydro-flattening was very effective as the shoreline was very flat with a low slope.

Sources

 LAS, tile index, and metadata for Lake County are from Illinois Geospatial Data ClearingHouse. NAIP imagery is from United States Department of Agriculture Geospatial Data Gateway. Breaklines is from Chicago Metropolitan Agency for Planning. Lidar LAS data for portion of the Chippewa Valley is from The City of Eau Claire, WI.