National Map Point Selection

( Only works on 1/3 arc second gridfloat files )

What happened to all the old USGS DEM files ? ? ?
If you still have DEM files, see my old DEM Point Selection page.


Latest Update Apr. 8, 2019
( Fixed multiple occurences of notes window.   Works from 26th to 72nd parallel ).



Nedwv1.exe Point Selection

( Get points by window selection )


You can't select points until you zoom in to a 7.5 minute window.
The window below shows the maximum number of points you can extract.
You can zoom to a 5 or 2.5 minute window and pan across 7.5
minute lines, but the location marks disappear.

If you need an area larger than 5 minutes that crosses the 7.5
minute lines, try the program below that uses upper left lat / lon
and distance east / south to select points.



You can reduce, but not increase the number of col / rows selected.
You can estimate the output file size based on # of col / rows removed,
coordinate input and / or file type.




National Map Download


This program only works on 1/3 arc second
GridFloat files from the National Map.



Go to the National Map download page.

Program Notes

This program extracts points and attempts to match the ground under your feet, but you'll
have to enter your own coordinate system  It's not perfect.  See description below.

USE AT YOUR OWN RISK !

Ellipse Used:  Major Axis-6378137m   Minor Axis-6356752m

You only need to extract the header (*.hdr) and float (*.flt) files into the same directory.
The *hdr is a small text file that defines the lat / lon,  number of cols / rows,  approx. cell spacing, etc.
The *flt is a 4 byte floating point file with 10812 cols / rows of elevation data. (467597376 bytes)
Each file has a 2 second (6 pt) overlap boundary around the core data.  UL data pt = row7, col7.



Longitude point distances are fixed by the ellipse radius at the center of each file.  The latitude distances
are based on an isosceles trapazoid.  If you project points north, it just creates a trapazoid based on the
starting row of points selected.  Rectangular grids use the same latitude distance at the center of points
selected and probably work best for small selections.

If you don't like these point definitions, you can write an elevation only comma separated (*.csv)
point grid or a binary (*.flt/*.hdr) file to define the points differently.  The *.hdr file
defines the upper left point and the cellsize depends on the number of col / rows removed.



Right click and "Save Target As" to download both files  NED_FILE.ZIP (83,105 bytes)



Nedbx1.exe Point Selection

( Get points by lat/lon and distance east/south )


        



WARNING !

This progam has no limitations on how many points it will write.
It only warns you once if you write more that 200K points, but will
actually write all 116 million points in any file if you're not careful.

USE AT YOUR OWN RISK !

Right click and "Save Target As" to download both files  NED_FILE.ZIP (83,105 bytes)





Other Links

Go to Contour Lisp Page.

National Map  download page.

Back to Home Page.