Global Mapper Pro

Convert elevation raster to las

I'm trying to convert an elevation raster to a las point cloud (one point per grid cell).  I have tried exporting the raster by right clicking on it in the Overlay Control Center and exporting as a las file and I have also tried selecting the raster in the Overlay Control Center then using the File > Raster export (and selecting las as the format).  Both options create a point dataset that must have data in it (it is a decently large file), but when I open the file it appears blank (nothing appears on the screen, regardless of coloration settings).  Several times I've also gotten an error message saying that the file is empty. Could someone help me out with this workflow?  I'm sure it's simple, but I can't seem to get it right.  Thanks.

Answers

  • Mykle
    Mykle Global Mapper User Trusted User
    What version of Global Mapper are you using?
    Do you have a LAS option under File > Elevation export?
  • I have Global Mapper v 13.0.7 (64-bit) (+Lidar).  
    I do have the File > Export > Export Elevation grid.  I've tried using Export Elevation grid to convert my .tif file to LAS (by selecting Lidar LAS file in the tool's first dropdown menu). When I load the exported file I get an error message (attached) and it takes a while to load points, but then nothing shows up in the map (a LAS layer does appear in the Overlay Control Center).  I checked in Windows Explorer, and the exported .las file is of appropriate size, so I think it contains data... but it just isn't read in correctly or something).  
    I've also tried different visualization schemes on the LAS layer that shows up in the OCC -- both using the toolbar and using the LAS layer's options in the OCC, but neither has made the las point cloud 'appear' in the map.
    The tif is projected in UTM 18N WGS84, and looks normal when I load it into the map.... I'm not sure what else to check for....
  • One other thing, with regards to that error message -- In Lidar Load Options I checked all the boxes in the 'Select Lidar Point Classification to import' and in the 'Select Lidar Return Types to Import' because I'm not sure what value the Export tool assigned to the 'lidar points'... perhaps this was where I went wrong?
  • bmg_bob
    bmg_bob Global Mapper Programmer
    I recommend first getting the latest release of Global Mapper 16.

    Did you look at the list of classifications and return types on the Lidar tab of the Configuration dialog to make sure that they are all enabled? 

    I exported a LAS file from a GeoTIFF and was able to import it successfully in both GM 16 and GM 17.
  • jddewitt
    edited January 2016
    Apologies -- I mistyped my version -- I have v16.0.7 now.  I'm in the process of upgrading to v17.  And I made sure to enable all the return types and classification types in the configuration dialog -- it takes a while to 'load' the LAS file, but nothing shows up when it's finished.
  • bmg_bob
    bmg_bob Global Mapper Programmer
    If you are still having this problem after you upgrade to Global Mapper 17, I recommend that you send an e-mail describing your workflow and the results, with a copy of your data (original GeoTIFF and output .las file), to Blue Marble Geographics support (geohelp@bluemarblegeo.com).  This will ensure that the support team sees the problem and can provide you with a timely response.  Thank you.

  • Mykle
    Mykle Global Mapper User Trusted User
    Are you doing all of your work in Global Mapper, or are you using Global Mapper to export files for use with another program?

    This is somewhat redundant: Note that a LAS file contains points.  They may include elevations for the points.  As you move your cursor around, the bottom line will show the elevation at the cursor.  If you choose "Always Draw Points at Fixed Size" with a small setting like "1", you may only see points.  If you choose "Automatically Enlarge Points When Zooming", and you set Draw Mode to "Use Colors if Present (Elevations Otherwise)" you may see the area colored according to the current shader.  Note that Hillshading is not available with a point cloud, but you can generate an elevation grid and then use Hillshading.  

    I created an elevation grid from a vector file of contours, and exported it to an elevation LAS file.  On import I see the area colored according to the shader (except daylight and slope shading).  

    I also exported the elevation grid to an elevation TIFF file.  On import I see the area colored with the selected shader, including hillshading.  

    I have not looked at elevation files exported as raster TIFF or raster LAS.  I would not expect either of these to display elevations, but only the colors displayed during export.  However, Global Mapper may provide more flexibility than what I expect. 

  • jddewitt
    edited January 2016
    Ok I updated to Global Mapper 17, and I'm still having the problem.  When I load the LAS file (making sure to Select ALL types of classification values and return numbers), it takes a long time to load the points, and then in the OCC the layer says there are 44,809,894 features in the file and the elevation bar is more-or less the right elevations (I have the Lidar toolbar set to Color points by RGB/Elev), but the map area is just the default pale yellow.  I also tried the 3D view and nothing shows. (See attached screen shot)

    I did a test run with a second TIF, I got the same result -- which is weird, because I know I have viewed LAS points that I exported from the second TIF using GlobalMapper in the past.  

    In response to Mykle: I did try changing the LAS layer's options to 'Always Draw Points at Fixed Size' and setting it to something very large (10).  Still nothing...

    So I'm thinking this has to be something basic like a projection issue (both TIF and LAS files are in UTM28N WGS84... I can't find the vertical coordinate system in the info) or perhaps it's an issue with my main map view setting?
  • jddewitt
    edited January 2016
    I just downloaded a 'real' lidar LAZ file from EarthExplorer, and it loads perfectly.  The points show up correctly, and are colored according to Elev. 

    It seems like the issue might be how the Export procedure is reading my tif DEM and assigning the X,Y, and Z values in the output LAS file?  I'm not sure how to test this though...
  • bmg_bob
    bmg_bob Global Mapper Programmer
    jddewitt said:
    Ok I updated to Global Mapper 17, and I'm still having the problem.  When I load the LAS file (making sure to Select ALL types of classification values and return numbers), it takes a long time to load the points, and 
    ...

    Can you post a screen capture of the Lidar Load Options you are using?  This would let me load a file using the same options.
  • bmg_bob
    bmg_bob Global Mapper Programmer
    I exported a GeoTIFF as LAS, then successfully imported the LAS using the same settings you are using.  I note that you are using "Use Global Setting from Toolbar" for your Draw Mode.  What is the draw mode on your Lidar toolbar?  Does changing it make a difference?

    If that doesn't help, I recommend that you send an e-mail describing your workflow and the results, with a copy of your data (original GeoTIFF and output .las file), to Blue Marble Geographics support (geohelp@bluemarblegeo.com).  This will ensure that the support team sees the problem and can provide you with a timely response.
  • I have a problem with point cloud
  • Dear 
    i have just checked the document and the screengrabs in it  you have used Global mapper V13?  can you please check it in GM16 
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