Profile Path Strange Result Across Lidar Data and 3D Point

jd2adams

Hello Global Mapper Community:

Can you help me troubleshoot what I am seeing in the Profile Path? The Profile Path is acting strange when I try to display a 3D point with the lidar data. With Display 3D point enabled, the lidar points and 3D point flatten out and all display at 0m and the Profile Path Y axis scale shows zero to -1,000,000 m. Without 3D point display enabled, the lidar data looks great.

I am running GM 24.1 (b030923)

The scenario is we collected our first base station point with a new Emlid RS2+ and want to see how it lines up with existing lidar data available from USGS 3DEP. We forgot to record the GNSS receiver height so, yes, we know it is not going to line up perfectly. We are just running through the steps.

The RS2+ was setup on top of a building in Oakland, CA.

Here are screen grabs of the good Profile Path without Display 3D Point and bad Profile Path with Display 3D Point enabled:

To recreate my steps:

1) Download this 3DEP lidar file:

https://rockyweb.usgs.gov/vdelivery/Datasets/Staged/Elevation/LPC/Projects/CA_AlamedaCounty_2021_B21/CA_AlamedaCo_2_2021/LAZ/USGS_LPC_CA_AlamedaCounty_2021_B21_w6069n2103.laz

2) Open a fresh Global Mapper. No other data loaded so no Projection has been set.

3) Drag and drop the lidar LAZ file into Global Mapper window and load with default settings.

4) Your GM should now have Projection set to SPCS US Survey Feet CA Zone 3 (FIPS 403) NAD83 (NSRS2011) EPSG::6420

5) Import our Base Station Point from one of these two TXT files. The Projection information is in the filename. I focused on the SPCS file and just changed the horizontal units from feet to meters.

OPUS_Point_for_GM_SPCS_0403_CA_3_Meters_NAD83_2011_Geoid_18_Meters.txt

OPUS_Point_for_GM_UTM_10N_NAD83_2011_Geoid_18_Meters.txt

6) Zoom into the point. Here is an example Zoom level:

7) Draw a Profile Path across the point you just created and set the Distance from Path to Show to 0.5 meters.

8) Toggle the "Draw 3D Point Features in Path Corridor" On and Off.

9) Does your Profile Path behave the same as mine?

That is it.

For another test, I used the Lidar QC Tool to see the difference between the 3D point and lidar.

As I expected, the ELEV_DIFF is 0.2949 m which gives me a warm fuzzy our 3D point and lidar are in the same ballpark.

Thank you All for listening and any insights you can provide.

Joe

BMG_Amanda

Hello. Judging from your screenshots it seems like the point feature is being assigned the no-data elevation value "-999999" possibly during import. Your import settings seem fine and obviously the QC tool is reading the elevation correctly, so hopefully this can be resolved with a fresh build of Global Mapper. I followed your steps using today's build (b070623) with OPUS_Point_for_GM_SPCS_0403_CA_3_Meters_NAD83_2011_Geoid_18_Meters.txt and the path prof worked as expected. You can grab a fresh build here: https://www.bluemarblegeo.com/products/global-mapper-daily-builds.php

jd2adams

Thank you so much Amanda for testing this with the Daily Build. I thought about that (oh if only more time) but wanted to get this information out there anyways.

I will be watching the Blue Marble website for the next official GM release and see if the fix made it in.

Thank you again for monitoring this forum and supporting us.

Joe