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Murphy presentation

  1. 1. Accuracy Assessment of LiDAR Data Using ArcGIS 10.1 Presented By: Niccole Murphy Advanced GIS Concentration
  2. 2. Presentation Overview  Project Goals  Guidelines  History of LiDAR  LiDAR in ArcGIS  Comparison of LAS Dataset Vs. Terrain Dataset  Code Structure  Final Output  Conclusion  Questions
  3. 3. Project Goals  The goal of this project was to determine if ArcGIS 10.1 could be used to assess the accuracy of LiDAR Data  The accuracy was measured against eight statistics:  95th Percentile  95 Percent Confidence  Average Residual  Minimum Residual  Maximum Residual  Average Magnitude  RMSE  Standard Deviation
  4. 4. Guidelines  ASPRS Standards:  95 Percent Confidence no greater than 24.5 centimeters  95th Percentile no greater than 36.3 centimeters  USGS Standards:  Percent grade of slope no greater than 10%
  5. 5. History of LiDAR  LiDAR: Light Detection and Ranging  Conceptually been around since 1676  Technology and processing came around in the 2000’s  ArcGIS 9.3 (released in 2008) was the first to introduce LiDAR capabilities
  6. 6. LiDAR in ArcGIS 10.1  First accepted in two formats: ASCII and LAS  Need to convert to a multipoint feature  Version 10.1  Introduced LAS Datasets  Added ability to view in 2- and 3- Dimensional formats  Version 10.2 changed little, but increased the efficiency of the LAS Dataset to handle larger sets of data
  7. 7. LAS Dataset  Does not import the data, stores reference to the data’s location  Need a license for either 3D Analyst or Spatial Analyst  Can view the data in 3-Dimensional format  Profile view available  The purpose is not to analyze the data, but to check the quality of the data  Requires data to be classified  Limited to 1-2 million points per LAS file (up to 100 MB in version 10.1)
  8. 8. LAS Dataset Continued  LAS Dataset toolbar allows for different visual techniques  Point Display: Elevation, Class or Return  Surface Analysis: Elevation, Aspect, Slope and Contour  Need to convert to another format to perform analytical operations
  9. 9. Terrain Dataset  Contained within a Geodatabase and stored as a Feature Class within a Feature Dataset  Should use a projected coordinate system  It is a multiresolution, triangulated irregular network (TIN)  Surface is generated on the fly in the form of a TIN  Although similar to a TIN, it does vary from a TIN
  10. 10. Terrain Dataset Continued Terrain Dataset TIN Can be stored in a Geodatabase Cannot be stored in a Geodatabase, rather it is stored directly on a disk Maintains the connection to the source data/measurements from the data it was created with Once it is created the tie to the original source data is lost Has no size limit Recommended to have only a few million nodes, but has a maximum limit of 10-15 million nodes Cannot be visualized in 3D using ArcScene (can use ArcGlobe though) Can be visualized in 3D using ArcScene Is edited by modifying the source measurements Is edited by modifying the triangulation * Derived from Esri Virtual Campus Course (Managing LiDAR Data Using Terrain Datasets
  11. 11. Code Structure  The Script tool requires two input features:  The surface to be used  Can be Terrain, TIN, DEM, etc. (Anything that contains elevation information)  The file containing check point information  Other features of the tool:  Sets the workspace for the outputs  Prompts for a name of the output table  Choose fields containing orthometric height values and geoid separation values
  12. 12. Prepare Outputs Is the LiDAR Data in Orthometric or Ellipsoidal Heights Orthometric Ellipsoidal Calculate Ellipsoidal Height of Check Points Calculate Residuals Generate Absolute Residual (Used in some Statistical Calculations Generate Statistics and Add to Final Output Table If the ‘Remove’ Field of the Check Point Data is Empty
  13. 13. Final Output
  14. 14. Conclusion  Can display LiDAR data using LAS Datasets and Terrain Datasets  LAS Dataset is good for visual quality control, but not analytical operations  Terrain Datasets can be used for analysis and to help answer questions  Although ArcGIS can perform some tasks on LiDAR data, it cannot be a replacement for software like Terrasolid
  15. 15. Questions?