Exporting LIDAR Data to Delta Z Imagery

Images produced by coloring LAS data by their elevation difference with respect to different point source IDs of the data (or different scanners for mobile data - see explanation of this option in step 12 below) are called Delta Z (dz) images or Color by Elevation Difference images. These images are used to visualize elevation differences between overlapping LIDAR flight lines and the mismatch between overlapping sources of LAS data. If there is no overlap of the LAS data in the pixel output, then the intensity of the LAS point that has highest elevation is set as the pixel value for Red, Green, and Blue bands.

Delta Z (dz) images are very useful for doing a quick assessment of the quality of the relative height match between overlapping strips. In a perfectly calibrated system with perfect GPS/INS data, we should never see a difference in height where strips overlap, because these points represent the same location on the ground.

LIDAR data is exported to dz imagery in TIFF format.

How to Export LIDAR Data to Delta Z Imagery

1. Open the LP360 Export Wizard by clicking the Export LIDAR Data command on the LP360 toolbar. The Export Wizard dialog will open with the Step 1 of 3 page displayed.

   

2. Click the arrow in the Export Type list, and select Surface.

   

3. Click the arrow in the Surface Method list and select Point Insertion.

   Learn more about surface methods

   

4. Enter a No-Data value for the output TIFF files.

   

5. Enter a Cell Edge Length greater than zero Map Units.

   

6. Under Surface Attribute(s) to Export, select dz Images.

   

7. Select the Dz tab that appears next to the Surface tab.

   

8. Select one of the following options: "Source ID Count", "dZ Value", and "Graphic". The "Source ID Count" option receives the number of unique point sources within given cells and writes those numbers as cell values into the output image. The "dZ Value" option writes the absolute dz values of the points within the cells as the cell values. The "Source ID Count" and "dZ Value" options produce .flt files (floating point images) and "Graphic" produces a tiff image.

   

9. Select the number of intervals (from 3 to 10) for the dz images in the Intervals list. Based on the number of intervals you set here, along with the interval size, the Range column in the table displayed below displays the elevation ranges and the Color column displays the color that will be used for the range next to it.

   

   Note - To change the color associated with a particular range, double-click the color box in the Color column and select a different color in the color selection dialog.

10. Enter an Interval Size for the images.

    

11. Select Absolute Values if you want to use the elevation difference between higher elevation and lower elevation of the LAS data in the ouput cell. If this option is not selected, the elevation difference of the highest point source ID and lowest point source ID is used as the elevation difference for the output cell. This elevation difference is used to color the pixels.

    

12. Enter a percentage in the Modulate source differences by Intensity to specify the intensity of the LAS point with the highest elevation to use in the cell. The range for this option is 0-100%. Zero percent will not show any features in the overlapping region, whereas 100% shows all features with the highest level of color.

    Note - As the color is applied to the overlapping region, the actual features in the area are lost. This option, Modulate Source Difference Intensity, is used to correct this issue. An example of output images generated using 4 intervals and 75% modulation

    

13. Select Between Scanners Only if you are using mobile mapping LIDAR data. Mobile data has different scanners rather than different strips and point source IDs. This option exports the dz images for the mobile data using different scanners. Select Generate Cell Shapefileto create a shapefile with a grid for the cells in the output.

    Note - For LAS 1.4 and above, the scanner number is obtained from the LAS point. For LAS 1.3 and below, the scanner number is obtained from its filename. An example of mobile data with the Between Scanners Only option used

    

14. Click Next.