Unable to form an elevation grid from 3D point data

SalaSala Global Mapper UserPosts: 9
edited October 2012 in Elevation Data
Hi All,

I am using Sean Tvelia's steps on How to Produce DEM is using Global Mapper and after Importing to 3D point data form, I am promted with an error msg: "Unable to form an elevation grid from 3D point data from ..." sa below.
Untitled.jpg

What seems to be my problem?
..:confused:

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    It sounds like 3D point data couldn't be found in the file that you were loading. What does the file that you are loading look like?

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • SalaSala Global Mapper User Posts: 9
    edited October 2012
    Hi Mike,
    Just checked my contour(tab file) and it only has Z(height) values.Could this be the reason why?

    cheers
    Sala
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    Sala,

    What does your .txt file that you are trying to grid have? The TAB file wouldn't make any difference if you are trying to grid a .txt file.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • SalaSala Global Mapper User Posts: 9
    edited October 2012
    Mike..
    Please find attached .txt file.txt file.jpg
    Contents are as such:
    DESCRIPTION=Unknown Line Type
    LINE_WIDTH=1
    LINE_COLOR=RGB(0,0,0)
    LINE_STYLE=Solid
    ZV2=480
    x=159.91381224
    y=-9.78474663
    602195.046,8917283.922,-999999
    602136.295,8917284.443,-999999
    602110.569,8917290.913,-999999
    602095.405,8917304.440,-999999
    602063.185,8917375.476,-999999

    thanks again.
    Sala
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    Sala,

    Ah it looks like you have lines with per-vertex elevations, but the Z for each vertex is -999999 which aren't valid at all. It appears that your actual elevation is in the ZV2 attribute. Try loading your data as 'Point, Line, and Area Features', then once you have the lines in, open the Options dialog for the layer and select to use the ZV2 attribute for elevations. Then right-click on the layer in the Control Center and select to create an elevation grid from the data. You might also try opening your .txt file in Notepad prior to loading it and do a search and replace on ',-999999' and replace it with an empty string to get rid of those incorrect elevation values.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • SalaSala Global Mapper User Posts: 9
    edited October 2012
    Good morning Mike,
    Apologies if this is too easy a question to answer but how can I "load your data as 'Point, Line, and Area Features" in GM.
    The rest of the steps is ok for me ..just this one.

    thanks again
    Sala

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    Sala,

    You are loading the .txt file using the File->Open Generic ASCII Text File menu command, correct? If so at the top-left of that dialog is a section where you select to load as 'Point Only', 'Point, Line, and Area Features', or 'Create Elevation Grid'. That is where you select it.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • SalaSala Global Mapper User Posts: 9
    edited October 2012
    Dear Mike,

    I posted this too late. I have been able to construct the DEM as you last said. However, when i load the layer on GM, the dark blue part of the DEM, lies outside the area of the coastline and reads as 20m. This I presume should be the sea and its reading as 20m. Have I done 1 step wrong or am i understanding the DEM incorrectly?+

    thanks again.
    Sala
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    Sala,

    It sounds like maybe you have contour data, correct? Is the lowest contour value perhaps the 20m contour and there isn't a shoreline vector (or there is one that doesn't have elevation)? To get the sea to be 0m in height there would have to be some data to indicate where the sea was. Typically this would be a shoreline vector that you assign a height of 0m.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • SalaSala Global Mapper User Posts: 9
    edited October 2012
    Mike,

    Yes. I have:
    - contour data
    - contour lowest value is 20m
    - shoreline vector is present (as a separate layer) and has attributes as VDC: 7 and Name: (null)

    I do not understand what the "7" in the VDC attribute mean( the shoreline was digitized by someone else thus I do not know what VDC stands for), could the 7 be the height of the shoreline? Attached is a copy of the shoreline feature information.
    Contour Line Feature Info.jpg

    Need your help.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2012
    I don't know what the VDC is, but I'm guessing you want your shoreline at an elevation of 0. Just press Edit and add an ELEVATION attribute with a value of 0, then try generating the elevation grid from the layer(s) with the contours and shoreline.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
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