Lab 7: LiDAR Remote Sensing
Introduction & Goal
The objective of this laboratory exercise is to help students develop skills in Erdas Imagine 2020 and ESRI ArcGIS Pro software that include essential basic knowledge on LiDAR data structure and processing. This lab generally helps students understand processing and retrieval of surface and terrain models and processing and creation of intensity image and other products that derive from the point cloud.
Methods & Data
When opening Erdas Imagine, we displayed individually LAS files and examined whether there are overlapping points at the boundaries of the tiles, because Lidar data tiles mostly have overlaps at the tile boundary to prevent void areas. We added all the lidar point cloud files provided by the UWEC Geography department (.las). After loading the .las files into the viewer, we were able to zoom into any tile of choice to see individual lidar points. We then utilized ArcGIS Pro for the remainder of this lab because it contains easier workflows compared to Erdas Point Cloud tools.
In this part of the lab, we learned how to generate a LAS dataset and explored lidar point clouds with ArcGIS Pro with the assumption that we are working on a professional project for the City of Eau Claire, WI, USA. The tasks that was included in this project includes 1) Create a LAS dataset, 2) Explore the properties of LAS dataset, and 3) Visualize the LAS dataset as a point cloud in 2D and 3D.
After opening ArcGIS Pro and creating a new project, we activated specific Esri Extensions (3D Analyst and Spatial Analyst) to help us. Afterwards, we created a folder connection to our LAS folder and created a new LAS dataset and named it Eau_Claire_City.lasd to input all individual LAS files. We noted the statistical and ancillary information the LAS data comprises. We utilized the Calculate tool to build statistics for the LAS dataset to view the quality control/ quality assurance (OA/OC) of individual .las files and the dataset. We then assigned coordinate information to the dataset with Horizontal Coordinate System: NAD 1983 HARN Wisconsin CRS Eau Claire (US Feet) and Vertical Coordinate System: NAVD88 (height) (ftUS). The LAS dataset was then dragged from the catalog into Pro.
Now that the dataset was successfully inserted into the viewer, we explored various display settings of the LAS data when Zooming into any of the two tiles. From the LAS Dataset Layer tab, and selecting Appearance, there are many different options on how to view the layer: Surface Elevation, Slope, Aspect, and Contour.
Figure 2) By utilizing the surface Elevation tool, the result shows a 3D TIN surface display of Half Moon Lake, Eau Claire, WI, USA
Figure 3) By utilizing the Slope tool, the result identifies the slopes of the earth around the area and in the lake.
Figure 4) By utilizing the Aspect tool, the result shows the direction each facies is facing. I thought this was a rather interesting tool when looking at elevation.
Next we utilized a New Local Scene view to ArcGIS Pro viewer. The data that is being displayed previous to this part of the lab are points with defined dimensions that were first return echos captured by the laser pulse data collection. After dragging our Eau_Claire_City.lasd from the Catalog pane to Scene view, there is a Classification tab within the LAS Dataset Layer tools. By clicking on Create from that menu, and drag a line over a bridge, we're able to explore various 3D views of the city when using the First-Person navigation tool. The purpose of this part in the lab is to show that LAS point cloud data is good for visualization, but products usually are shown as lidar derived products (i.e. Digital terrain Models (DTM), Digital Surface Models (DSM), contours, etc.).
The next part of this lab is to generate Lidar derived products by deriving DSM and DTM products from point clouds. The products are produced at the average of the Point Spacing field of the LAS Dataset Properties window. Raster derived products - including DSM, DTM, Hillshade of DSM, and Hillshade of DTM & a Raster Intensity Image- will be created.
Results
Figure 5) Digital Surface Model (DSM) Hill shade derived product created in ArcGIS Pro.
The surface features on Earth's surface, including buildings, vegetation, and water, are distinguishable in this product Interpolation on water surfaces can cause shaded anomalies in the image.
Figure 6) Digital Terrain Model (DTM) derived product created in ArcGIS Pro generated by Ground Return points of LAS point cloud data. Smooth texture and manmade structures/vegetation is not as visible.
Figure 7) LiDAR intensity image (TIFF)
Data Sources
- UWEC Geography Department
- Lidar Point Cloud and Tile Index, Eau Claire County, 2013
- Eau Claire County Shapefile, Mastering ArcGIS 7th Edition data by Margaret Price 2016
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