spot elevation

[Jack C 8]

Hi all. I was wondering if someone can guide me in the right direction. I need to find the highest spot elevations within a prescribed area. I know google earth has somethign where i can place my mouse and it will tell me the elevation where my cursor is BUT i would like to drag a box for example of say 10km by 10km and have it tell the the highest spot elevation within that area. Would REALLY appreciate your help on this one! thxJack

[GaryGB 10]

Hi Jack:GlobalMapper has the ability to:"generate isoheight area features in addition to contour lines as well as spot elevations at the highest and lowest points in the area over which the contours are generated"...when using the "Generate Contours" command on a loaded DEM file for your area of interest...I'm pretty sure this would be accessible in the GlobalMapper trial version:http://www.globalmapper.com/product/download.htmhttp://www.globalmapper.com/..Hope this helps! :-)GaryGB

[Jack C 8]

Hi Gary. Thats an awesome start for me. Have you used this program? I was just wondering when the program first opens do you just open a mesh file (an FS Genesis file?)from flight sim with it? Thanks bud. I have been waiting for a response from a bunch of different sites on this matter and so far you are the only one that can help. I appreciate it.Jack

[GaryGB 10]

Hi Jack:Your inquiry suggested that you want to look at elevation values, so will want a Digital Elevation Model (DEM) file..DEMs for the USA are found at: http://seamless.usgs.gov > View And Download United States Data.On the USGS Seamless Data Server "map" window, using the default "Magnifying Glass" tool icon under the left side menu bar "Zoom" menu, left click and drag the red selection rectangle to zoom in on the area of interest (be sure you allow sufficient time for the window to update FULLY (server gets busy sometimes!) before performing another function.Keep zooming in as above until you have the precise area you want selected.Next, under the left side menu bar "Downloads" menu, click the "dotted select rectangle" tool icon and then left click and drag the green selection rectangle to zoom in on the final area of interest in your DEM.When you release the left mouse button, a pop-up window titled "The National Map Seamless Server Request Summary Page" will submit your selection for approval.In that "Request Summary Page" pop-up window, click the "Modify Data Request" button; that window will now change into a scrollable list of data types and resolutions, with columnar choices as to file format.Again, be sure you allow sufficient time for the changed window to update FULLY, then carefully scroll down looking for the item checked in that list by default, and confirm that it says: "National Elevation Dataset (NED) 1 Arc Second"; if not, find the "NED 1 Arc Second" item and check it (that window will update again).Now on the same line in the pick lists to the right of the (checked) "NED 1 Arc Second" check box, be sure "GeoTIFF", "ZIP", "HTML" are selected, then at the very bottom of that window, click "Select Changes & Return To Summary".You should return to the original "Request Summary Page"; now just click the "Download" button and... wait... (server gets busy sometimes!).Global Mapper should be able to directly read the downloaded ZIP file (a DEM rendered as 32-bit elevation values in a GeoTIFF imagery file with most important geographic coordinates and other parameters in the file header); but if not, un-zip the file into a working folder.You would then open the GeoTiff in Global Mapper via File > Open data; when the DEM is loaded, go to File > Generate Contours and pick the functions you want from the sub-menus; in particular you would be interested in checking the "Generate Spot Elevations At Min/Max Values" check box."Tinkering" and testing various options in addition to reviewing the somewhat abbreviated documentation via "Help" is very conducive to learning... as long as one does not save the changes!It is usually best to save a Global Mapper "Workspace" rather than saving changes to the original data files.NOTE: DEMs must ALWAYS be in "WGS84 Projection" and in either of several compatible elevation data file formats in order to be successfully submitted along with an "INF" file for processing via the FS SDK "Resample" utility to then be converted into a terrain mesh file for FS.Other very important and precise considerations apply, so one must study the FS SDK documents carefully to make files that are actually usable by FS.Hope this gets you started! :-)GaryGB

[Jack C 8]

Hi Gary. Thanks again. I was looking more for Canada DEM but I found a site that I need. So I downloaded and followed your steps. Its works great. One simple tiny problem. I have to squint like crazy to find the high spot elevations. It shows a triangle with the elevation beside it. The triangle is tan color (or so). Is it possible to change the color of the triangle? As well the coordinates along the bottom are black. Those are very hard to read too. Can that color be changed too? Thanks Gary. This too helped big time.Jack

[Jack C 8]

Never mind Gary I foun dout how. But I am comparing the highest spot elevations to some spot elevations on my VNC charts and they differ by about 3-400 feet in some locations. Any idea as to why the difference? But the location is the same at least!

[GaryGB 10]

Hi Jack:On the Global Mapper menu bar, click Tools > Configure > Point Styles-tab > Point Types-pick list > Spot Elevation.Then again on the Point Styles Tab > Point Types-pick list > Symbol-pick list set at "Spot Elevation", click the "Select Label Font" button and set the Font attributes including Color.For the Spot Elevation Icon, apparently one can substitute a different colored version of the Icon in *.BMP or *.ICO format (edited in a graphics program such as Windows Paint).I did a very quick test on my 1280 x 960 resolution display setting using a screen grab of the Point Styles-tab, cutting out the gray inside of the frame to the right of the "Custom Symbols"-pick list Box and pasting into a new *.BMP file.Checking the size of the *.BMP file showed that it was 83 pixels tall x 95 pixels wide. I edited a screen grab copy of the tan triangle into a bright red on the Spot Elevation Icon and saved it as another *.BMP file; it was then usable from the "Custom Symbols" Pick List Box.PS: The higher resolution data sets will show a smaller number of meters or Arc Seconds between elevation data points in the DEM.I believe most of Canada does not yet have better than 30 Meter / 1 Arc Second resolution DEMs like the USA does, but if you do find any with higher resolution, it might be a better data set for your project.I've not studied up yet on technical production aspects of VFR Navigation Charts (VNC) Aeronautical Charts, but perhaps as with the "reported" Spot Elevations of airports, subjective "Field Observation" Spot Elevations may also sometimes be substantially inaccurate.This reportedly may be complicated by "Geoid Undulations"; (now I know what to blame my wobbly knees on after too much "liquid mischief" during a night out with old college chums!). :-lol :-beerchug Hope this helps you further with experiments on your own system! :-)GaryGB

[GaryGB 10]

Hi Jack:In answer to your question to the issue of elevation inconsistencies, perhaps these links might explain it better than I can...This Wiki article has a basic definition of geoid undulation:http://en.wikipedia.org/wiki/Undulation_of_the_geoidThe introduction of this article has some basic concepts:http://64.233.167.104/search?q=cache:YBeXj...clnk&cd=5&gl=usThis article presents the application of the concepts within the context of air navigation charts:http://64.233.167.104/search?q=cache:hu59R...clnk&cd=1&gl=usThis web page offers a Geoid Height Calculator for correction of geoid undulation with regards to elevations derived via GPS.http://sps.unavco.org/geoid/I wonder if ACES is already factoring in the Geoid and Ellipsoid corrections in their newest world model tesselation algorithms yet?Maybe Pete Dowson's new 8-core CPU FS computer could calculate this "on the fly" at runtime if ACES codes FS11 to be multi-core compatible! ;-) Hope this helps with the elevation variance issue! :-) GaryGB

[Guest dannydesiliva]

Is there a way to retreieve the spot elevation of a surface (without using the Terrain ->Label Spot elevation)....I need to use it for an attribute in a block in my routine.