Combine/Compare layers

zululuxzululux Global Mapper UserPosts: 39Trusted User
edited February 2015 in Elevation Data
Hello everyone,

I'm operating GM 14.2. I am using it more for Aeronautical work rather than pure GIS. I have two queries please:

I have a task at hand that requires me to find the maximum elevation in a series of defined areas.

Firstly, I need to combine the three DTM Layers correctly; Namely: Spot Height, Trig beacon, and 3 arc-sec layer (downloaded thru GM). I have used the Analysis-Operation: MAximum Elevation. From my understanding, this operation will select the maximum elevation at a particular X-Y/Lat-long between the two/three layers.

There appears to be an anomaly though: The Highest displayed Altitude on the Spot height layer is 11423ft. The highest on the Trig Beacon layer is 9846ft. When they are combined together, the new top elevation becomes 11384ft. Firstly, is this the correct process for comparing and getting the maximum elevations from each layer at any given lat-long/X-Y?

Secondly, why is the top elevation 39ft shorter?

The end result is for me to cut the resultant combined layer into sectors; and find the highest elevation in each sector. Is this possible?

Your assistance is appreciated.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2014
    Yes that is the proper method. I suspect you are getting hit by the alignment of the samples in the new grid layer along with bilinear resampling which is enabled by default for terrain layers. So the samples of the combined grid don't align exactly with your Spot Height layer samples and the samples by the maximum height are away from the sample center, so a blended value from nearby pixels is used. What you should do is first set the resampling method for the layers to Nearest Neighbor (No Resampling) on the Options dialog for the layers so you only get exact sample values and not interpolated values.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited April 2014
    Thanks very much mike. I'll try that. In the interim, I will also need to cut the resultant Combined Layer into different areas. Is there a function to find the highest elevation in each of these areas?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2014
    Yes, just select the area features with the Digitizer Tool, then right-click and select the option under Measure/Analyze to calculate elevation statistics in the selected areas. This will add attributes to each area with stats from the terrain, including the maximum encountered elevation.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Global Mapper
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited April 2014
    Thanks again mike. I will be re doing the later combination tomorrow. Just one more thing: I anticipate 100 sectors from the new combined layer. Is there a batch method of attaining elevation stats or must each sector be done one by one ? :confused:
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2014
    You can do more than one at a time. Just select them all with the Digitizer Tool first (draw a box around or hold down Ctrl when selecting to select multiple), then do the option to calculate elevation statistics for the selected areas.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited April 2014
    Ok. Thank you mike. I will also need to plot the location of said maximum elevations in these sectors. So far, my thinking is to export the area attributes including the x/y of the Mac elevation to csv. Thereafter I would re-format the csv and import the x/y points. Is this the only/most efficient way to achieve this?
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2014
    When you calculate the elevation/slope stats using the Digitizer Tool you should also be prompted to create point features at the min/max elevation values encountered. You could then export those points to a CSV file.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited April 2014
    You're the man Mike. Thanks. I'll try all of these and get back to you. Cheers.
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited July 2014
    Hi Mike,

    Hope you've been well. Thanks for the previous help.

    I have a nutcracker of a problem: remember I'd said I would need to to determine the max alt. in 100 sectors after combining a 3 terrain layers. I've more or less got the layer combination right. What's kicking my butt now is defining those sectors.

    The sectors are supposed to be comprised of 5 nm-diameter circles (Range rings) to 60nm. Thet in turn are intersected by 8 straight lines originating from a point less than 1 nm from the centre point of the range rings. This layout (see attached pic ) creates a number of arc-shaped areas growing in size from 5nm to 60nm.

    I need each of those curved shapes to be defined as an area so that I can stat. the max height of each area. The problem is that even if I convert the Range Rings to lines; they still behave as areas, which makes it impossible to split the intersecting lines into said sectors; then re-convert lines to areas ans stat. the elevation for each sector. I been trying for weeks with no joy.

    Can you please help?:(

    Regards
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited July 2014
    I have updated the range ring dialog to support creating radial areas rather than lines, so you should be able to easily create the areas that you need!

    I have placed new builds with the latest changes at the links below:

    32-bit: http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15.zip
    64-bit: http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15_64bit.zip

    Simply download the .zip file for the build that you are using and extract over your existing installation files. The likely locations to extract to are as follows:

    32-bit: C:\Program Files (x86)\GlobalMapper15
    64-bit: C:\Program Files\GlobalMapper15_64bit

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited July 2014
    Thanks very much Mike. I appreciate it. I'll let you know if it works. Does it include instructions? I have been hesitant to spend Money upgrading to V15; but from the customer service I've received, I think I will. I am planning to go to V15 end of July. Is that a good time, or will V16 be available soon instead.

    Regards,
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited July 2014
    Hi Mike,

    I have tried the procedure but get the error attached to screen shot. (Capture_snip.png)
  • stihlstihl Global Mapper User Posts: 52Trusted User
    edited July 2014
    Hi Zululux,

    You need to extract everything in that .zip to the installation folder of GlobalMapper and overwrite any files. The default location is:

    32-bit: C:\Program Files (x86)\GlobalMapper15

    64-bit: C:\Program Files\GlobalMapper15_64bit

    After that you can just start Global Mapper how you usually do through the desktop and it will be the updated version.
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited July 2014
    Thanks Mike. I've tried several times and continually get this error:
  • stihlstihl Global Mapper User Posts: 52Trusted User
    edited July 2014
    I'm not Mike, but I'll try and help you anyway.

    I just downloaded the 64bits file and it unzipped just fine. Can you try to right click on the .zip file and 'Run as administrator'. Perhaps unzip all of the contents to a temporary folder on your desktop and then move it to the GlobalMapper installation folder.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited July 2014
    You do need to first install the full v15 installer from Global Mapper Downloads, then do as stihl says as unzip to a temporary folder, then copy those in to C:\Program Files.

    We are planning on releasing v16 in September of this year.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited July 2014
    Dude, Am I understanding that I need to upgrade to V15 from V14 in order for this new feature to work?
  • JeffH@BMGJeffH@BMG Global Mapper Developer Posts: 322Trusted User
    edited July 2014
    zululux wrote: »
    Dude, Am I understanding that I need to upgrade to V15 from V14 in order for this new feature to work?
    Correct. The updates that Mike provided are only useful for Global Mapper 15.
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited July 2014
    Roger. Will upgrade and advise of result. Thanks for the help.
  • zululuxzululux Global Mapper User Posts: 39Trusted User
    edited February 2015
    Hi again Mike,

    Earlier last year, I had asked if it was possible to define the bottom and top elevations of a piece of airspace. For exapmle, the top elevation is 20 000ft and bottom elevation 14500 ft. How do I go about making these 2levels (20K ft and 14,5K ft) into a single piece of airspace with the accompanying volume for aeronautical planning purposes? I had tried the last instructions you gave me, but I couldn't get it to work; and I cannot find them on the forum anywhere either.

    Please help.

    Best regards,

    Zululux.
Sign In or Register to comment.