Provided by: terraintool_1.19-1_all 
NAME
terraintool — Generating surface meshes for cave survey software
SYNOPSIS
terraintool
DESCRIPTION
TerrainTool was written to create surface topographic data for the cave survey packages Survex (link to
URL http://survex.com) and Therion (link to URL http://therion.speleo.sk) using the results of the
Shuttle Radar Topography Mission (link to URL http://www2.jpl.nasa.gov/srtm/) (SRTM) in which the
shuttle Endeavour mapped the height of the Earth's surface between the latitudes 60 degrees North and 56
degrees South - about 80% of the Earth's land mass. Published resolution was 1 arc-second for the US and
its territories and 3 arc-seconds elsewhere. The latter corresponds to about 90m at the equator. The
resulting data is royalty-free and, for many countries, may be the only data publicly available.
TerrainTool is able to automatically download the "tiles" of data that it needs, directly from a USGS
server.
Because the SRTM radar imaging worked by using an oblique scan of the earth's surface, it had problems
with shadowing where, despite multiple passes, areas remained hidden, resulting in voids in the data.
This is particularly noticeable in mountainous areas. A subsequent project Advanced Spaceborne Thermal
Emission and Reflection Radiometer (ASTER) (link to URL
http://www.jpl.nasa.gov/news/news.cfm?release=2009-103) used infra-red nadir-viewing camera (i.e.
directly downward) which, in post-processing over multiple orbits created stereo images from which height
could be derived. This overcame the shadowing problem but the view could be obstructed by cloud and
vegetation cover and suffered from "artefacts" - spurious features which are by-products of the imaging
process. On it's own, the ASTER Digital Elevation Model (DEM) is unsuitable for cave surveying.
Finally complete in February 2020, NASA released a new DEM by re-processing "global" 1 arc-second SRTM
data and carefully filling in the voids with re-processed ASTER data. The result, NASADEM, is thus the
highest resolution void-free near-global DEM that we have available. The only disadvantages are
• The tiles are typically 9 times the size of the 3 arc-second SRTM data, so they take longer to
download and process and occupy more disk space
• You need to be logged into an Earthdata account to download the data. Unfortunately, TerrainTool
cannot to do this for you so auto-download is disabled. However, signing up for an Earthdata
account is quick and easy at https://urs.earthdata.nasa.gov/users/new/ (link to URL
https://urs.earthdata.nasa.gov/users/new/)
With the completion of NASADEM, this release of TerrainTool uses it as its only source of data.
Having logged in to your Earthdata account, you can find the NASADEM data by going to
https://lpdaac.usgs.gov/products/nasadem_hgtv001/ (link to URL
https://lpdaac.usgs.gov/products/nasadem_hgtv001/) ) selecting "Access Data" and "Download Data" next to
"Data Pool" and clicking on the directory link will take you to a huge page containing all the tiles,
currently at https://e4ftl01.cr.usgs.gov/MEASURES/NASADEM_HGT.001/2000.02.11/ (link to URL
https://e4ftl01.cr.usgs.gov/MEASURES/NASADEM_HGT.001/2000.02.11/) Please note that this URL might be
subject to change without notice. The page can take several minutes to download so don't panic if your
browser freezes! Tile files are the ones ending ".zip" and preceded by the relevant lat/long e.g.
NASADEM_HGT_n52w003.zip You can download tiles with a browser. Do NOT try unpacking the zip files -
TerrainTool reads them in zipped form.
TerrainTool does the following:-
• Converts between the spherical (Lat/Lon) coordinates used in the tiles and a variety of map
coordinates used by cave surveyors so that the surface mesh and cave survey can be combined in a
single model based on the local map coordinate system. Coordinate systems currently supported
include British (OSGB) grid, Irish grid, UTM, French (Lambert conical projections), Austrian grids,
Slovenian Grid and New Zealand's NZMG and NZTM2000. The internal design is intended to allow
additional coordinate systems to be added easily.
• Re-samples the data using biaxial interpolation to create a rectangular mesh of user-specified
spacing.
• Displays a coloured topographic map of the mesh.
• Adds a user-specified offset (3-D) to the coordinates to align with coordinates used for the
underground survey.
• Saves the mesh as surface data in Survex (.svx) or Therion (.th) format.
The programme, written in Java, provides a conventional GUI-style interface and will run under Windows,
Solaris, macOS and Linux operating systems.
"TerrainTool" was written by Mike McCombe who is very grateful to UBSS for giving it a home. Please feel
free to contact Mike with feedback or requests for help at mikemccombe <at> mikemccombe.co.uk or via the
Survex list (link to URL http://survex.com/maillist.html) .
Driving Instructions
TerrainTool is a conventional GUI-based application with a menu bar and dialog boxes to gather user-
information. To get started, do the following:
1. If you already know which tiles you will need from the NASADEM dataset, download them now and save
them in the data directory. This is ~/.local/share/terraintool/ by default, or
$XDG_DATA_HOME/terraintool/ if $XDG_DATA_HOME is set. Otherwise, when you try to create the mesh,
TerrainTool will provide an error message to say which tile it needs and where to store it.
2. Select the required coordinate system using the Options menu.
3. Go to Create on the File menu to specify the size, location and resolution of the mesh.
4. Save the results as in Survex (.svx) or Therion (.th) format
5. Use Survex to process the file and Aven to view the results in 3D. Remember to enable viewing of
surface legs in Aven!
6. Use the Offset command in the Options menu to fully align the terrain data with the coordinates
used in your survey.
7. When generating surface data in Therion format, Therion needs to be told the coordinate system used
for the surface data in a form that it recognises (e.g. EPSG:27700). See the description of the
surface command in the Therion Book for more details.
8. Incorporate the terrain data into your survey project.
File Menu
Create... is used to calculate the terrain mesh. A dialog box is used to gather the following:-
Create dialog items
Item Meaning
Grid Reference The grid reference for the mesh, expressed in the current
coordinate type. This point can be at the centre of the mesh, any
of the corners or the mid-point of any of the sides (see below). An
example in the correct format is shown below the text field.
E-W Range The distance (in metres) between the East and West edges of the
mesh.
N-S Range The distance (in metres) between the North and South edges of the
mesh.
Spacing The distance (in metres) between adjacent cells in the mesh.
Grid ref is at Specifies where current point (see "Grid Reference"
above) lies in relation to the boundaries of the mesh.
Pressing OK starts the calculation of the mesh points. The NASADEM tiles need to be availale in the data
directory $XDG_DATA_HOME/terraintool ("$HOME/.local/share/terraintool" by default if $XDG_DATA_HOME is
not defined.
At the end of the calculation, results are displayed as a simple coloured relief map. The mouse position
is displayed (in current coordinates) in the message bar on the bottom edge of the frame.
Lat/Long... provides a means of defining the current point in terms of latitude and longitude, rather
than as a grid reference. If the point can be represented as a valid grid reference in the current
coordinate system, it is used to initialise the "Grid Reference" field of the "Create..." dialog box.
Likewise, the current grid reference is used to initialise the Lat and Long fields with the latitude and
longitude of the current point.
Latitude and longitude values can be expressed as either
• real values in degrees (e.g. 46.25), where negative values are West / South, or
• values in degrees, minutes and seconds (e.g. 46 N 15' 22.6")
Latitude and Longitude are usually based on the WGS-84/GRS-80 datum and ellipsoid. The user may select
alternatives, which will cause the lat and long values to be re-calculated.
Save as...
Once a mesh has been calculated, the "Save as..." command can be used to save the terrain data. Normally,
this will be in Survex (.svx) or Therion (.th) format.
Otherwise, height values are defined for each point in the mesh. Easting and Northing values are those
of the current coordinate system.
Options Menu
Coordinates...
This is used to select the type of coordinates to use. The following are currently supported:
Coordinate Systems
Coordinate System Description
Austrian T{
The Austrian (BMN) coordinate system, in three zones
T}
Irish Grid T{
The Irish grid system, used in both Northern Ireland and the
Republic of Ireland.
T}
Lambert 93 T{
The Lambert 93 coordinate system. A conformal conical projection
occasionally used in France.
T}
Lambert (5 zones) T{
The coordinate system most commonly used in France. Three zones (I,
II and III) cover North, Central and Southern France. Zone IV is
used in Corsica. A fifth zone (II-extended) covers the whole of
France, at the expense of greater distortion.
T}
NZMG T{
New Zealand Map Grid - New Zealand's coordinate system superseded in 2010. Maps
based on this are no longer available, but still widely used. Based on a conformal
orthomorphic projection.
T}
NZTM2000 T{
New Zealand Transverse Mercator, successor to NZMG.
T}
OSGB T{
Ordnance Survey of Great Britain - the normal British grid system.
T}
Slovenian Grid T{
A Transverse-Mercator grid used in Slovenia
T}
UTM T{
Universal Transverse Mercator, devised by the US Department of
Defense to cover the globe (except polar regions) in 60 zones. Also
used by many national mapping agencies, often with a national or
regional datum instead of WGS84.
T}
One of the design objectives of this software is to be able to add further coordinate systems with
minimal difficulty.
Selecting a coordinate system from the drop-down list results in automatic selection of sensible defaults
for the datum and ellipsoid. The user is free to override this selection using the other two drop-down
lists. Whilst, for example, OSGB invariably uses its own datum and the "Airy Sphere", other systems are
frequently used with a variety of datums. UTM, for example, is used in Spain with the European (1950)
Datum and Australia with their own (MGI) datum.
Offset
This provides a simple way of adding a fixed 3-D offset to mesh point in the mesh as it is saved. You
might want to do this because
• Your cave survey coordinates might not use the full easting and northing values
• The height values differ from "known" surface heights in your survey. SRTM heights are referenced
to EGM96 (Earth Geopotential Model 1996) and may be significantly offset from a national height
datum.
AUTHOR
This manpage was generated from the online documentation at
http://www.ubss.org.uk/terraintool/terraintool.php, which is also reproduced in
file:///usr/share/doc/terraintool/README.html. Permission is granted to copy, distribute and/or modify
this document under the terms of the GNU General Public License, Version 3 published by the Free Software
Foundation.
On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-
licenses/GPL.
Terraintool(1)