Global Mapper v25.0

Local max/min elevation

orjanwallers
orjanwallers Global Mapper UserTrusted User
edited November 2011 in Suggestion Box
Hi,

Searching the forums for tips about finding local max/min elevation or running batch/script powered absolute max/min, I came up with a couple of old threads. Some answers hinted that this is already on the to-do list; any ideas about possible implementation time-frame? Also, it would improve not having to generate any contours when trying to find max/min elevation.

Related forum threads:
http://www.globalmapperforum.com/forums/suggestion-box/6074-ridgetop-peak-contour.html
http://www.globalmapperforum.com/forums/elevation-data/5265-coordinates-max-min-elevation.html
http://www.globalmapperforum.com/forums/technical-support/3273-calculate-max-elevations-each-ridgetop.html

Thanks in advance!

Comments

  • global_mapper
    global_mapper Administrator
    edited November 2011
    You can currently right-click on an elevation layer in the Control Center and select an operation to find the location of the minimum and maximum values in the layer. Is this kind of what you want, but available from a script?

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • orjanwallers
    orjanwallers Global Mapper User Trusted User
    edited November 2011
    I have missed this new feature but it doesn't really do what I want. How does it really work?
    I did a quick test and the Find Extreme function returned three different locations but only one max elev value. The three positions seem to be one elevation cell apart (in this case 30 meters on DTED2 data). None of the points were actually 3341 meters but rather 3339,771; 3340,25 and 3340,252 respectively.

    Example:
    Maximum Elevation: 3341 m
    Location(s) of Maximum Elevations:
    -82.8740277778, 9.1226388889
    -82.8740277778, 9.1223611111
    -82.8740277778, 9.1220833333

    Does the function always return three positions? Or does it return all positions for the max elevation value found? And what elevation value is actually used?

    What I'm looking for is a way to assign a local search area, preferably by a search polygon, and then find the local extreme values within that search area.

    Use case; find highest point in each 10'x10' square for guiding low level flying. Use a pregenerated shapefile with 10'x10' grid and then batch run the local max/min function and return a point layer with positions and attributes for each max/min values.
  • orjanwallers
    orjanwallers Global Mapper User Trusted User
    edited November 2011
    I forgot to mention I'm still on GM 12.02 so there might be improvments in GM 13 that I'm not aware of.

    (Couldn't find a way to edit my previous post. How do I do that?)
  • global_mapper
    global_mapper Administrator
    edited November 2011
    The function from the Control Center will search the raw elevation values of each layer and report the location(s) of the absolute maximum and minimum values. So if there are multiple samples with the same elevation each location will be returned.

    However, given your extended description I think I have a better solution. You can create your areas of interest, then select them all with the Digitizer Tool, then right-click and select the option to calculate elevation statistic attributes for the areas. This adds attributes to each area with things like the min and max elevation in the area. Starting with v13 2 additional attributes, MIN_ELEV_POS and MAX_ELEV_POS are also added with the location of the local minima/maxima in the area, so you could use that to get the information that you need added to each layer.

    I can think of some easy changes to Global Mapper that would allow you to get a point layer from that data. Just let me know if this works in concept and I can make those changes.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • orjanwallers
    orjanwallers Global Mapper User Trusted User
    edited November 2011
    I just did some tests with v13 and the current concept works fine so far. The resulting max/min values are stored as attributes to the polygons. Now, if you could just add the ability to get all the MAX/MIN_ELEV_POS into a point file it would be a really great feature!

    Many thanks, Mike!
  • global_mapper
    global_mapper Administrator
    edited November 2011
    I have updated the elevation area statistics to create separate MIN_ELEV_POS_X, MIN_ELEV_POS_Y, MAX_ELEV_POS_X, and MAX_ELEV_POS_Y attributes. I have placed a new build at http://www.globalmapper.com/global_mapper13.zip with the change for you to try. Simply download that file and extract the contents into your existing v13.xx installation folder to give it a try. If you are using the 64-bit v13 version there is a new build at http://www.globalmapper.com/global_mapper13_64bit.zip .

    So with this once you have added the elevation statistics, use the File->Export Vector Data menu command and export to an area Shapefile. Then, use File->Open Data File and load the DBF file (note NOT the Shapefile) that was created as part of the Shapefile export and choose either the MIN_ELEV_POS or MAX_ELEV_POS attributes to use for the X and Y. Then on the Options dialog for the DBF layer that you just loaded choose the correct elevation attribute (i.e. MIN_ELEV or MAX_ELEV) and you are set!

    Let me know if I can be of further assistance.

    Thanks,

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