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Utilities dem2fds

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Glenn Forney edited this page Aug 10, 2017 · 28 revisions

Notes on creating FDS input files from digital elevation map (dem) files using the utility dem2fds. dem2fds is a utility installed along with FDS and Smokeview that may be used to convert elevation and image data obtained from the USGS website https://viewer.nationalmap.gov/basic into FDS input files.

Preliminaries

  • Download and install Smokeview from https://pages.nist.gov/fds-smv/downloads.html. This download provides the utility dem2fds used for creating FDS input files.

  • Download and install Imagemagick from http://www.imagemagick.org/script/binary-releases.php. This program is used to convert terrain image files from jpeg 2000 to jpeg format.

  • Go to the USGS National Map website at https://viewer.nationalmap.gov/basic to obtain elevation and terrain image data files for the region of interest. These files are used by dem2fds to create FDS input files. This website has a map of the United States on the right and a set of data download options is on the left. Zoom in on the region of interest then download elevation ( Elevation Products (3DEP) ) and terrain image ( Imagery - 1 meter (NAIP) ) files using the steps described below.

USGS dem webpage

Obtaining elevation data:

  1. Select the Elevation Products (3DEP) checkbox.
  2. Select 1/3 arc-second DEM checkbox
  3. Select the GridFloat File format option
  4. Click on the map and zoom in to a region of interest.
  5. Click on the Find Products button. You should see one or more entries listed with headings beginning with USGS NED 1/3 arc-second ...... 1 x 1 degree .
  6. Click on the Footprint link to verify where various files are located.
  7. Click on Download link to download files of interest.
  8. Unzip these files using a program such as Winzip. Open the directory created with the unzip operation and copy the .flt and .hdr files to a directory where you'll keep your elevation and image files.

Obtaining terrain images:

  1. Click on the Return to Search button and uncheck (if checked) the Elevation Products (3DEP) checkbox
  2. Select the Imagery - 1 meter (NAIP) checkbox
  3. Click on the map and zoom in to a region of interest within the elevation region selected for for elevation files.
  4. Click on the Find Products button. You should see one or more entries with each entry beginning with m_ and ending with .jp2 .
  5. Click on the _Footprint- link to verify image file locations.
  6. Click on Download link to download files of interest. The image files should cover the region you are using to define an FDS input file.
  7. Copy the downloaded files to the same directory you used to copy the .flt and .hdr elevation files.
  8. The .jp2 files you just downloaded are in jpeg 2000 format. They need to be converted to jpeg format . To do this on a PC, run the jp2conv command. On Linux or a Mac, run the jp2conv.sh command. These commands are installed with the latest version of Smokeview.

Put the downloaded elevation and terrain files in a directory. This directory may then be referenced by dem2fds using the -dir command line keyword when creating a FDS input file.

Creating an FDS input file from dem data

  • Create a dem2fds input file named casename.in containing the following
GRID
 ibar jbar kbar
 LONGLATMINMAX
 longmin longmax latmin latmax

The integer parameters ibar, jbar and kbar are used to define the IJK keyword of the FDS input file's &MESH namelist.
In dem2fds, these parameters correspond to the number of longitude and latitude divisions and the number of divisions along the z direction respectively. The decimal parameters longmin, longmax, latmin and latmax are the minimum and maximum longitude and latitude values enclosing the region being modeled.

Two other methods for specifying a terrain region are to use the LONGLATCENTER or LONGLATORIG keywords as in

GRID
  ibar jbar kbar dx dy
  LONGLATCENTER
  longcen  latcen

or

GRID
  ibar jbar kbar dx dy
  LONGLATORIG
  longorig  latorig

where dx and dy are the scenario width and length in meters ( ibar, jbar and kbar are defined as before), longcen and latcen are the longitude and latitude at the scenario center, i.e. at position (dx/2, dy/2) and longorig and latorig are the longitude and latitude at the scenario origin, i.e. at position (0.0, 0.0).

  • Finally, create an FDS input file, by running the command:
 dem2fds -dir elevation_directory casename.in

where elevation_directory is the path of the directory containing the elevation and image files downloaded previously and casename.in is the file containing GRID and LATLONG... keywords.

  • To view the resulting case, run the commands:
fds casename.fds
smokeview casename

Overview of dem2fds Input Keywords

  • GRID - Specifying the simulation grid
GRID
 ibar jbar kbar dx dy zmin zmax

ibar, jbar, bar - number of divisions along the x, y and z directions dx, dy - distance along the x and y axis.

Note, dx and dy are required if LATLONGCENTER or LATLONGORIG are used to specify a terrain region and optional if LATLONGMINMAX is used to specify a terrain region (dem2fds computes dx and dy for LATLONGMINMAX keywords).

zmin, zmax - minimum and maximum z elevation. These parameters are optional.

  • LONGLATCENTER - specifying the longitude and latitude at the scenario center
LONGLATCENTER
 longcen latcen

longcen, latcen - longitude and latitude at the center of the scenario, at position (dx/2,dy/2) .

  • LONGLATORIG - specifying the longitude and latitude at the scenario origin
LONGLATORIG
 longorig latorig

longorig, latorig - longitude and latitude at the origin of the scenario, at position (0,0) .

  • LONGLATMINMAX - specifying longitudes and latitudes that bound the scenario
LONGLATMINMAX
 longmin longmax latmin latmax

longmin, longmax - minimum and maximum longitude latmin, latmax - minimum and maximum latitude

dem2fds Command Line Options


dem2fds (SMV6.5.3-57-g038cc8b) Jul 28 2017
Create an FDS input file using elevation and image
  data obtained from http://viewer.nationalmap.gov 

Usage:
  dem2fds [options] casename.in
  -dir dir  - directory containing map and elevation files
  -elevdir dir - directory containing elevation files (if different than -dir directory)
  -geom     - represent terrain using using &GEOM keywords (experimental)
  -obst     - represent terrain using &OBST keywords 
  -help      - display help summary
  -help_all  - display all help info
  -version   - display version information
  -elevs    - output elevations, do not create an FDS input file
  -matl matl_id - specify a MATL ID for use with the -geom option 
  -overlap - assume that there is a 300 pixel overlap between maps.
  -show     - highlight image and fds scenario boundaries
  -surf surf_id - specify surf ID for use with OBSTs or geometry
  • The -obst option is used by default.
  • The -geom option is experimental testing the new geometry file format.
  • All terrain images should contain a 300 pixel overlap buffer. However this is not always the case. The -nobuffer option is used for those cases when there is no overlap between two adjacent images.

Examples

Data files used for the Devils Tower examples may be downloaded from here. These files were generated using the steps outlined previously. The .jp2 files do not need to be downloaded unless you want to experiment converting image files from jpeg 2000 to jpeg format.

  1. Devils Tower I

Devils tower is located in north eastern Wyoming.
This region was chosen as a test case because it is easy to verify (or not) that the geometry and the overlayed image generated by dem2fds is consistent at the tower location.

  • dem2fds input file:
GRID
 100 100 30
LONGLATMINMAX
 -104.7256 -104.7096 44.5850 44.5945

The IJK portion of the &MESH line in the FDS input file is

&GRID IJK=100,100,30, XB=...
  • create an fds input file using:

dem2fds -overlap -dir terrain\tower tower.in

where terrain\tower is a directory containing elevation data and terrain images for Devils Tower.

  • The image below was created by running FDS on the input file generated using dem2fds then viewing with smokeview using:
fds tower.fds
smokeview tower.fds

devils tower

  1. Devils Tower II

This example is similar to the first. It uses the -show command line option of dem2fds to add file names to the terrain images and to show a red rectangle for the region being simulated. This is useful for ensuring that the correct elevation and image files are being used and if not which ones should be downloaded.

  • dem2fds input file:

The longitude/latitude region is larger than in the first example. It corresponds to the region of the data files that were downloaded rather than the region being modeled.

GRID
 100 100 30
LONGLATMINMAX
 -104.7256 -104.7096 44.5850 44.5945
  • create an fds input file using:

Again, the -show option is used to hilight the region being simulated and identify the files that were downloaded.

dem2fds -overlap -show -dir terrain\tower tower.in

where terrain\tower is a directory containing elevation data and terrain images for Devils Tower.

  • create the following image using the commands:
fds tower.fds
smokeview tower.fds

devils tower

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