Working with Topography Data and 3D Relief in the GEON IDV
You can use the GEON IDV to show high-detail topography data for any region on earth.
Displays can be contour lines, maps colored by elevation value, or true 3D relief displays.
You can also
drape images over topography data values to make 3D relief displays.
How to run the IDV and connect to data
To install and start the GEON IDV, see
Download & Run the GEON IDV.
To load data in the GEON IDV, see
Choosing Data Sources and Connecting to Data Sources.
There is information below about putting
focal mechanism
data in formats for the IDV.
Topographic Displays
All these different kinds of displays were made from latitude-longitude grids of altitude values.
Click on an image below to see full size.
Contour data plots can be combined with any other IDV display type.
How to make the displays is after the pictures.
Antarctica, 500 m contours (click to see full size image)
Contour lines on Mt. St. Helens (100 m interval)
(USGS DEM data). Click to see full size image.
Topography of New York State colored by elevation
(NGDC 30 second "GLOBE" data). Click to see full size image.
3D relief of Mt St. Helens with satellite photo draped over the surface;
vertical exaggeration is 1:1 (USGS DEM data). Click to see full size image.
Topography of Antarctica colored by elevation.
Click to see full size image.
(NGDC ETOPO2v2 data)
Topography of Arctic basin, oblique 3D relief, colored by elevation (and North pole!).
Click to see full size image.
(NGDC ETOPO2v2 data)
Arctic basin, 500m contours (click to see full size image)
Making Displays
First set the display to a
map projection (map area)
suitable for your data, and then set the
vertical scale
suitable for your data.
When you
connect to a data source the Dashboard shows the "Field Selector" for that data.
To make a display,
in general you choose (click on) a Field name in the "Field Selector" tabbed panel in the Dashboard, then click on a display type
in the Displays panel of the same window, and then click on the "Create Display" button.
All topographic data should have Field type "Elevation" or "Altitude," and the Displays panel shows
choices such as "Plan Views-> Color Image" to make false color images from the elevation values,
"Plan Views->Contours" to make contour line plots of the data, and
"3D Surface->Topography" to make a surface draped over the topography.
Click on the Displays type you want, then click on
the "Create Display" button. You can also show contour lines on the 3D topography.
When a display is made, the Dashboard shows the "display control" panel for that display.
You can use the display control to change contour line values, coloring of contour lines, or the color table used to color
a 3D relief surface which can be colored by elevaiton.
You can drape a surface photograph over 3D topographic relief. You must know the latitude/longitude
location of the corners of the photograph. Then make an ".xmg" file describing the photo.
See Imagery Mapped with Latitude and Longitudes. With this file you can put the photo in an IDV display as a flat image at any level.
Use Displays choice "Imagery -> 3 color (RGB) Image."
To drape a photo in an .xmg file over 3D topography, load the .xmg file as your data choice, then
use the Displays choice "Imagery -> 3 color (RGB) Image over topogaphy." Click "Create Display." The IDV
will show a window for you to click on which of your data sources has the topogrphic data for the area of
the photo. When you do that the display is made.
To save demands on your computer, only use topo data that covers your area. In the Dashboard, Field
selector, do right click on the Data Source name of the topo data. Choose menu option Properties.
Use tab Spatial Subset. Drag the map outline to your area. This only works with gridded NetCDF data, not with
DEM files.
Topography Data Sources for the IDV
First check the ready-to-use data files in the section "Topographic Data Files for the GEON IDV Online" below.
The IDV reads latitude-longitude grids of altitude, topographic data, from two kinds of files, DEMs (digital elevation
model files), and NetCDF files.
An excellent source of topographic data for the IDV is USGS DEMs
(Digital Elevation Models). The IDV is built to read these
DEM files directly. The IDV should read and display any DEM file with filename ending in ".dem"
For the USGS 1:250,000-scale Digital Elevation Models, go to http://edc.usgs.gov/geodata/.
These have a horizontal resolution of 3 arc-seconds: the
spacing of the elevation values is 3 arc-seconds (roughly 100 meters). The vertical resolution is
the nearest integral meter at each grid location.
Use the "Alphabetical List" to find the name of the USGS 1:250,000 topo map that covers your area.
Save the DEM file for that map's area; there is an eastern half and a western half file for each map.
Each file covers one by one geographic degree.
To find a map name for your area, use a online map search such as
http://topographicalmaps.com/250k.mgi?state=wa (for the state of Washington in this case).
Unzip the downloaded file; it gives one file with no extension such as "hoquiam;"
add the extension .dem, to make a filename such as hoquiam-e.dem.
You can connect the IDV to a .dem file and it should be ready to use.
From http://edc.usgs.gov/geodata/ you can get higher resolution 1:24,000 scale DEMs
(resolution near 10 meters), and other
topographic data.
There are also 2 arc-second DEMs (about 62 meters resolution horizontally); see
http://rockyweb.cr.usgs.gov/elevation/2arcinfo.html.
For lower resolution, for any place on the earth, use the three global topography data sets provided online
by the U.S. National Geophysical Data Center (NGDC), the
ETOPO5 (5 minute resolution in lat-lon, about 10 km) topography data set,
ETOPO2 (2 minute resolution in lat-lon, about 4 km) data set,
and the "GLOBE"
(30 second resolution, about 1 km) topography data set.
For information about these data see NGDC web sites for
ETOPO5 (http://www.ngdc.noaa.gov/mgg/global/etopo5.HTML),
ETOPO2, and
GLOBE. The GLOBE topography data does not include the seafloor; all values there appear to be -500 meters;
the ETOPO2 set does have the sea floor.
For tips about downloading topography data from the NGDC web sites for the IDV, see
NGDC topo data conversion notes.
To convert the NGDC ascii files to the NetCDF file format needed for use in the IDV,
use the UNAVCO interactive data converter.
To make NetCDF topography data files for the IDV see
GEON IDV Data formats.
The GEON IDV uses
NetCDF formatted data. To make 3D relief displays, the data
variable must be called "Altitude." In the Field Selector window
you should see "Altitude" in the Fields panel when topography data file is selected.
3D relief displays in the IDV
may be computation-intensive; with a large topography data set
your IDV may basically freeze up. First try making least demanding topography display, a color image.
Choose Displays type "Plan views -> Color image."
Use of a topography 600 by 600 array or
more, to make 3D relief plots, may basically freeze up computers running the
IDV with 512 RAM allocated for the IDV. To increase performance, you may be able to
increase memory use by the IDV. See
GEON IDV How-to;
"Increase memory for performance" section.
Memory allocation of 512 megs will make 3D relief plots of a
750 by 930 data array, though you will have to be a little patient.
GEON IDV Topography Color Tables
IDV displays use a "color table" to associate every data value with a color to display each data value.
The IDV comes with many color tables, and a powerful editor tool to modify color tables and make new ones.
Color tables are a very effective way to highlight data of interest,
show patterns in data, and generally make displays more understandable and meaningful.
The right color table will highlight important features in your data.
See Color Tables
Color tables control transparency of the surface. You can make a relief surface that
is partly transparent so you can see features below it. If this does not seem to work,
try changing the order that displays are created.
Color tables for GEON IDV topography displays include the following:
"Topography US - Pacific Northwest"
is for the eastern US Pacific Northwest and areas of
approximately similar climate, such as the
northeasten US, Europe, and Japan. The range for Topography 2 is -25 to 4000 meters.
"Topography US - Rocky Mountains" is designed for
the high, dry parts of the western United States,
and for areas of similar climate and elevation,
Be sure to use its native range, -2450 - 3700 meters.
"NGDC topography relief (UNAVCO)" is best for ocean bathymetry.
Be sure to use its native
range, -11000 to 9000 meters.
Topographic Data Files for the GEON IDV Online
Cut and paste the URL into the IDV Data Choosers URLs entry box, or save the file to your local disk and
enter its file path into the IDV Data Choosers Files entry box.
Topography grids of 30 second horizontal resolution (near 1 km),
not including seafloor; integer meters elevation values:
US, Alaska, western (52 to 72 N, 151 to 170 W):
http://geon.unavco.org/unavco/TOPO/US_Alaska_west_GLOBE_30sec_topo.nc
US, Alaska, eastern (54 to 72 N, 130 to 151 W):
http://geon.unavco.org/unavco/TOPO/US_Alaska_east_GLOBE_30sec_topo.nc
US, western (31 to 50 N, 114 to 129 W):
http://geon.unavco.org/unavco/TOPO/US_western_GLOBE_30sec_topo.nc
US, Rocky Mountains (31 to 50 N, 104 to 114 W):
http://geon.unavco.org/unavco/TOPO/US_Rockies_GLOBE_30sec_topo.nc
US, plains (24 to 51 N, 92 to 104 W):
http://geon.unavco.org/unavco/TOPO/US_plains_GLOBE_30sec_topo.nc
US, midwest (24 to 51 N, 80 to 92 W):
http://geon.unavco.org/unavco/TOPO/US_midwest_GLOBE_30sec_topo.nc
US, eastern (24 to 51 N, 67 to 80 W):
http://geon.unavco.org/unavco/TOPO/US_eastern_GLOBE_30sec_topo.nc
Europe, 30 sec resolution, western (12W to 4E):
http://geon.unavco.org/unavco/TOPO/Europe_west_topo_30sec.nc
(click here to see Europe topo data area, all 3 parts)
Europe, 30 sec resolution, central (4E to 20E):
http://geon.unavco.org/unavco/TOPO/Europe_central_topo_30sec.nc
(click here to see detail of central Alps as 3D relief)
Europe, 30 sec resolution, eastern (20E to 35E):
http://geon.unavco.org/unavco/TOPO/Europe_eastern_topo_30sec.nc
Other resolutions or areas:
US, 48 states, 4 minute horizontal resolution (near 7 km):
http://geon.unavco.org/unavco/TOPO/US_topo_4min.nc
US, 10 minute resolution (near 18 km):
http://geon.unavco.org/unavco/TOPO/US_topo_10min.nc
Europe, 2 minute horizontal resolution, including seafloor (data spacing <= 4 km):
http://geon.unavco.org/unavco/TOPO/Europe_topography_2min.nc
(click here to see 2 min. Europe topo data area)
Antarctica, 4 min. topography (south of 60 S, including seafloor)
http://geon.unavco.org/unavco/TOPO/Antarctica_4min_topo_etopo2v2.nc
Arctic, 4 min. topography (north of 55 N, including seafloor)
http://geon.unavco.org/unavco/TOPO/Arctic_topo_4min_etopo2v2.nc
Japan, 2 min. topography, including seafloor
http://geon.unavco.org/unavco/TOPO/Japan_topography_2min.nc
Tonga-Fiji region, 2 min. topography, including seafloor
(click here to see area covered)
http://geon.unavco.org/unavco/TOPO/Tonga_Fiji_topography_2min.nc
More Sample Topographic Displays and Data
Tonga - Fiji region topography, 3D relief oblique view, colored by elevation
Yellowstone National Park and Grand Teton National Park 1 km resolution, oblique view
data is
http://geon.unavco.org/unavco/NETCDF/YNP_GTNP_topography_30sec.nc
Colorado Front Range 3D Relief, 1 km resolution, oblique view
data is
http://geon.unavco.org/unavco/TOPO/FrontRange_north_topography_30sec.nc
California, 2 minute resolution, oblique view
data is
http://geon.unavco.org/unavco/NETCDF/California_topography_2min.nc
European topography, 2 minute resolution, overhead view
and
the Alps, 2 minute resolution, overhead view
data is http://geon.unavco.org/unavco/TOPO/Europe_topography_2min.nc
Japan, 2 minute resolution, oblique view
data is
http://geon.unavco.org/unavco/TOPO/Japan_topography_2min.nc
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Comments or questions about this page? Send e-mail to Chuck
Meertens (meertens unavco.org).
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