Creating dz Images

Relative vertical accuracy, or flight line offsets, or the swath-to-swath fit between flight lines or drive passes can be qualitatively assessed using dz images. Or quantitatively assessed by exporting and analyzing the values. The USGS LiDAR Base Specification has evolved over the years with some different recommendations for evaluating interswath (overlap) consistency, and there are other variations such as the ASPRS Positional Accuracy Standards for Digital Geospatial Data that can provide more detail on the specific values to use. Each of our supported product lines can produce these dz images.

GeoCue Workflow Management Software

  1. Populate working segments.
  2. Create LIDAR Ortho entities for the desired areas or over the entire working segment layer(s).
  3. Set the Image Generation Parameters to generate dz images.
Example of dz images generated by GeoCue
dz Images in GeoCue

LP360

One can display the data by Elevation Difference for a quick assessment, but it is usually best to Generate a dz image or value raster using the Export Wizard since the display is dependent on the points retrieved from the files as dictated by the pyramid files and zoom level. The Export Wizard can quickly produce the rasters to remove the variability. You can further analyze the relative accuracy between flight lines with the Seamline Analysis tool to help verify quantitative compliance with the ASPRS Digital Accuracy Standards.

TerraScan

Generate a dz image by first exporting a biggest distance lattice model and then using those values to generate a raster using your desired schema.

  1. Compute Distance using line average z.
  2. Export a Lattice Model of the Max Distance at your desired grid spacing.
  3. Import the exported lattice model file(s) from Step 2 into a new project.
  4. Use the Export Raster Image option to generate the desired DZ image raster. You have complete flexibility for the color table used for this export and you can save a desired color schema if you set up a user defined color table.
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