Lidar GPS times not displaying enough precision
JJK
Global Mapper UserTrusted User
Mike,
I've encountered two issues with lidar attributes in a .las file, and am wondering if they are just settings that I can tweak:
1. I'm trying to identify individual lidar returns by their unique pulses (return #1, #2, #3, #4 for pulse #1, etc.). The GPS times in our data were spec-ed to have enough precision to allow unique time-stamps for each pulse. This is confirmed by using the vendor's proprietary LAS viewer (for example, GPS time = -17990670.91966).
However, GM v 15.1.7 only displays one place to the right of the decimal (-17990670.9 -- see attached image #1), which isn't enough precision to identify unique times. This low precision is carried through when exporting the .las points to a shapefile or another .las file. It is also displayed in the search dialog (see attached #2). Is there a way to show and use the full value precision?
2. While playing around with #1 above, I noticed that the attributes shown in the Feature Information tool window (see attached #1 again) do not exactly match those shown in the search window (attached #2 again). Specifically, Feature Info has both RETURN_CNT and RETURN_NUM, while Search only shows RETURN_CNT. I want to search on both of these attributes, but can't. Is there a way to turn on the RETURN_NUM attribute in the Search dialog?
Thanks
- John
I've encountered two issues with lidar attributes in a .las file, and am wondering if they are just settings that I can tweak:
1. I'm trying to identify individual lidar returns by their unique pulses (return #1, #2, #3, #4 for pulse #1, etc.). The GPS times in our data were spec-ed to have enough precision to allow unique time-stamps for each pulse. This is confirmed by using the vendor's proprietary LAS viewer (for example, GPS time = -17990670.91966).
However, GM v 15.1.7 only displays one place to the right of the decimal (-17990670.9 -- see attached image #1), which isn't enough precision to identify unique times. This low precision is carried through when exporting the .las points to a shapefile or another .las file. It is also displayed in the search dialog (see attached #2). Is there a way to show and use the full value precision?
2. While playing around with #1 above, I noticed that the attributes shown in the Feature Information tool window (see attached #1 again) do not exactly match those shown in the search window (attached #2 again). Specifically, Feature Info has both RETURN_CNT and RETURN_NUM, while Search only shows RETURN_CNT. I want to search on both of these attributes, but can't. Is there a way to turn on the RETURN_NUM attribute in the Search dialog?
Thanks
- John
Comments
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I've made RETURN_NUM be a searchable attribute in the search dialog.
I also made the GPS_TIME formatting be more intelligent. It will examine the first 512 points in a point cloud and determine how much precision to show based on the smallest encountered time delta rather than just always showing 1/10th of a second precision.
I have placed a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v15.xx installation folder to give it a try. If you are using the 64-bit v15 version there is a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15_64bit.zip .
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation -
Terrific - thanks, Mike!
- John
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