National Map Service - Lidar Downloads

TBC Work Processes (Info Only) TBC Point Cloud Work Process
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This question was raised recently and I have been looking into the processes to work with the data

The issue raised was as follows

I have a project that is at a defined location where I know the Latitude and Longitude of a point and I go to the National Map Service at TNM Download v2 and search for 3D Lidar files for the area of interest defined by the latitude / Longitude of the point.

The files that you can download from this site have an associated metadata file which is an XML formatted file that you can open with a text editor like Notepad or an XML file editor as per the free XML editor from Microsoft. In the file you will be able to find the details of the Coordinate System used to create the Lidar file e.g. UTM 15N or NAD83(2011) ALBERS etc.

You want to find the EPSG number for the Coordinate System - if it is not listed in the file or on the website - go to Google Search and type in e.g. NAD83(2011) Albers and it should come back with more details of the coordinate system e.g. EPSG 6530.

The EPSG is a unique identifier assigned to each coordinate system - you can type that into TBC Change Coordinate System command to find it and set the appropriate parameters.

The process steps are as follows

  • Use the National Map downloads site to find the Lat Long location
  • Find the LIDAR files that you are looking for
  • Check the metadata file for each lidar file to determine the coordinate system information and Units of the file (these are often in Metric (1000m Tiles)
  • Start a TBC project in e.g. US Survey Feet
  • Use Project Settings - Coordinate System to set the Coordinate System Projection and Datum using the EPSG number or Coordinate System and Zone settings derived from the XML file.
  • Import the Lidar LAZ file and select Metric as the units of the file and then select Grid Scaled in the Project Coordinate System to import the file. Note if you are importing several files and each file is defined in a different coordinate system, then you can select Grid Scaled in the selected coordinate system - then for each file you select the coordinate system details that are relevant and TBC will convert the data from the files coordinate system into the TBC Project Coordinate System for you.
  • Turn on the TBC Background Map Service to show the Street Map or Background Map (Satellite Image) for the area of the Point Cloud data.

Now that you have the Point Cloud data in the TBC project you can create a boundary e.g. from a KML file or imported CAD file or you can draw a boundary around the area of interest.

Use the RPS Command Point Cloud by Boundary from the Tool Shed menu to select the area of the Point Cloud(s) that you are interested in - having selected it use the Create Point Cloud Region from the Point Cloud Menu to create a Point Cloud Region of the selected data. You can now turn off all f the Point Cloud Regions except the one that you just created.

You can now do one of the following on the point cloud region to reduce it

  • Use the Sample Region command, select Spatial or Random mode of sampling - if Spatial input your desired point spacing e.g. 2’ and if Random input your desired sample size e.g. 0.2 for 200000 points of the source point cloud data. This will downsize the point cloud for you. The output is a Sample Point Cloud Region with the data points that are sampled out of the source data set.

Alternatively

  • Use the RPS Point Cloud Processor command to process the data - try using parameters of 25, 2.5, 0.6, Mean, No - note you can apply your boundary(s) here also and it will also create you a surface model from the sampled data.

Note that the source Lidar may have Tree Canopy and other data (cars etc.) in the data that you may want to clean out prior to sampling or processing with Point Cloud Processor.

In the RPS commands - Press F1 to access the help for those commands to better understand the tools and how to use them.

In this next video we show you how to process the data by Sampling and Creating Regions in a variety of ways including TBC and RPS standard Tools. You can also use the Extract Classified Point Cloud regions command to separate Trees from Ground etc

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