# Modern Geodata Management: Application of Interdisciplinary Interpretation and Visualization in Central America

Authors: T. Damm; H.-J. Götze
Journal: International Journal of Geophysics
 (2009)

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## Abstract

In the last years new methods of data acquisition and processing in geosciences, inspired by growing computer performance, have led to an increased amount of data, and this development will proceed surely. In this paper we present the conception and technical realization of an interdisciplinary research group's geodata management as a combination of a metadata catalog together with web mapping technology. Clearly related with the storage and retrieval of different datasets is the need of visualization. 3D visualization in geoscientific interpretation is a useful tool, if numerous, heterogenic datasets have to be visualized at the same time. Moreover, advanced sensing technology often generates native three-dimensional datasets. Using a case study from the Collaborative Research Centre “SFB 574”, we present the possibilities of our stereoscopic projection system and want to explain the benefit of 3D visualization for research in general and university education in particular, as low-cost systems become available nowadays.


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## Body

## 1. Introduction

The Collaborative  Research Centre “SFB 574”—Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger
Mechanisms for Natural Disasters (SFB574 [1])—is hosted
at the “Christian-Albrechts-University zu Kiel” and the “IFM-GEOMAR”. It is
funded by the German Research Foundation (DFG) and these institutions. The
center is organized in three research areas—“Subduction zone processes and
structure”, “Fore-arc volatile turnover and fluid flow”, and “Slab-arc-atmosphere transfer”. These three research areas actually are represented by 13
subprojects working in different fields and with different geoscientific
methods, for example, active and passive seismology, magnetics, electromagnetics, heat
flow, hydration analysis, sedimentology, vent fluid and water column analysis,
petrology, isotope tracers, and volcanology. As over fifty researchers are working on different
geoscientific aspects of subduction processes, data management and presentation
using internet technologies like web mapping is crucial for any interdisciplinary
cooperation.One prerequisite for
cooperation in multidisciplinary projects is the knowledge about available data—not just for the data administration. The increasing amount of SFBs digital
databases causes needs for extensive data documentation to guarantee their
long-term use and avoid redundancies. As flexibility
is needed in a big interdisciplinary research project (like a
“Collaborative Research Center”) regarding the acceptance of data
formats, consistent data documentation can just be achieved by use of a well-defined (-documented) metadata catalog structure, describing main aspects of
each single piece of data—either stored directly in a spatially-enabled
database or saved as a data file in specific formats.The development of a
metadata information system also facilitates the query of suitable spatial
information over the internet. The most significant ability of the internet
module is the presentation of new datasets from laboratory work, field
research, and remote sensing together with metadata of diverse geoscientific
data in a way to make it more useful to scientists but also to the interested
public. Based on an earlier version (e.g., Mohr and Götze [2] or Götze et al. [3]),
the actual SFB web site has been  turned into a geo-service tool, which provides
data, metadata, and numerical tools for 3D modeling, mapping, and visualization.
This is achieved by the introduction of a metadata catalog providing detailed
descriptions for each dataset. Coupled to this catalog is a web mapping
solution based on the “UMN MapServer” project [4] from the University of
Minnesota, which dynamically can plot datasets from the catalog. These two
parts interact with a content management system for static page content and a
database driven part for dynamic content, a seamlessly integrated web portal
has been formed. As it is open to the public audience, coupling points with
external researchers and other research projects can be discovered. Also efforts are made to strengthen the
collaboration and data exchange with partners from the participating countries
of Central America and colleagues from the US Margins program.The authors of this paper
were responsible for the collection and storage of data and laboratory
information from the entire SFB 574 working groups and our research partners in
a user-friendly, online environment. In particular, we, the Geoscientific
Information System  (GIS) group, are focusing on the construction of an easily
accessible database system, visualization of different data types, statistical
data research, and installation of both a GIS and a Meta Information
System (MIS) for the project. The full MIS system is accessible over the internet at
the SFB 574 website.We will conclude this
introduction with some general remarks on GIS specific issues. Many
geoscientists, who are modeling and using GIS software, do not generally deal
with geometric entities like “point”, “line”, “triangle”, “cube”, or
“polyhedron”. They are accustomed to think in terms of “fault planes”,
“rivers”, “geological formations”,  or “increased reflectivity”. Most of us like
to have access to the geometry of the “Liquiñe-Ofqui-Fault” in South Chile,
rather than to “lines 17 through 218”. This fact leads directly to
the definition ofgeo-objects, which
may be defined as “existing geoscientific objects, composed by a name, geometry
and a thematic description” (as discussed by Breunig [5]). For those users
involved in complex interpretation of interdisciplinary and heterogeneous
geodata, GIS methods and functions, which are based upon a geo-object data
structure, become important. It is clear, that object-oriented database
management will affect most of the tasks related to geosciences (3D/4D models,
visualization, validation, geostatistics, and more) but still broad access to
this technology in a uniform way is a bottleneck for this approach.Geologists and
geophysicists often work with objects that are composed of different geometries
and parameters (e.g., temperature, pressure, petrological composition).
Furthermore, they are linked to each other by complicated relations varying
through time.As an example the Mohorovičić discontinuity
(Moho), is a well-known entity
with a complex structure which can illustrate the mentioned problem. A “MOHO”-geo-object could be defined as follows:(1)
the lower boundary
of bodies with crustal densities;(2)
a line (2D) or
surface (3D) across which the p-wave velocity increases abruptly;(3)
the surface at which
topography becomes isostatically balanced;(4)
the interface
between rigid crustal material and weak lithospheric material. A tool for object
definition should provide the following functions:(1)
the ability to
define geo-objects with composite geometry, and(2)
the ability to link
several geometrically independent objects corresponding to the same
geo-object. Some of these features
are implemented in the in-house software package IGMAS [6, 7] standing for
“Interactive gravity and magnetic application system”; IGMAS+ is a new
JAVA software and is replacing the older IGMAS software
(http://www.gravity.uni-kiel.de/igmas/) which has been used for modeling both Central
America and Central Southern Andes (e.g., Kösters [8], Wienecke et al. [9], Melnick and Echtler  [10], Tašárová [11], Lücke
[12]).


## 2. Technical Requirements

In the planning period,
the  formerly  existing web page of the SFB 574 was analyzed and inspired by the
data management of the former SFB 267 (Mohr and Götze [2], Ott et al. [13])
and their website structure, an improved concept for an integrated web portal
driven by a MySQL [14] database, was
developed (cf. Figure 1).Figure 1
Behind the scenes of our data
management. Using the apache web server [15] and a MySQL [14] database, we
are using the “ConPresso Content Management System” [16] for static content. Dynamic content is managed using
the PHPdbRelations toolkit [17] with its export routines for HTML and XML
through PHP [18] (see also Williams and Lane [19]). For web mapping, the
UMN MapServer [4] (refer also to Mitchell [20] and Erle et al. [21]) is
used via the PHP/Mapscript [22] framework.We like to mention that
no commercial software was used. The “ConPresso Content Management System” [16]—free for academic use—was improved by
integrating “PHPdbRelations” [17], a
system, which was developed by one of authors (Damm). Essentially, it is a web-based tool for creating and modifying database tables and relations.
Generalized export routines for web content have been programmed; for example,
the queried content can be simply listed, put into tables, or sent as XML.The content is divided
into database tables with strictly defined relations between them. This might
be clarified by a practical example. Let’s say, Table 1 is hosting all datasets
of the SFB, and Table 2 is a second one that hosts the SFB cruises in the
Pacific Ocean. The relation, that a dataset was acquired on a particular cruise,
might be relation number 51. Then a call to a pseudofunction PHPdbRelationsEXPORT (“Datasets_T1(Cruise_R51)”)
would give a list of all datasets together with the cruises undertaken to
acquire these datasets. Of course, that is a simplification, as more features
like filtering or sorting are implemented but in principle a call for a
desired dataset results in human readable macrocode on user-level. That is the
intention of PHPdbRelations.Not just the content but also the data
organization structure can
be updated from the PHPdbRelations administration page. Database tables can be created or erased, columns added
or removed. Furthermore the relations can be modified, if a structural change
requires it. PHPdbRelations thus is not just useful for geoscientific web
portals; but moreover it is a general metacontent management system dealing
with single pieces of information in contrast to classical content management
systems, which work pagewise.For the implementation of
the metadata catalog, the use of PHPdbRelations gives enough flexibility to
adopt also existing projects to future standards without the need to migrate to
other systems.


## 3. Web Portal

Implementing the PHPdbRelations
toolkit into the SFB 574 website not just affected the data portal but also brought
datasets into relation with their creators, the cruises, or campaigns undertaken
to retrieve them or the measurement location. Even more, the same system
manages all other information like seminar talks, SFB publication, and even
personal data like email addresses, rooms, or telephone numbers in a structured
manner. This approach allows us to keep all these different pieces of information up-to-date using one central point—the PHPdbRelations administration web page.Moreover, this website is
expanding the strict hierarchical structure implied by the usage of menus and
submenus. Website-internal links bring information into their context as they
break the top-bottom hierarchy. In Figure2 an example of this website-internal
linking is shown. There is no extra administrative effort anymore, for instance,
to create a page for each subproject, that brings together all references corresponding
to, for example, publications, meeting talks, posters presented, and datasets in the
metadata catalog. For further details you can follow direct links to
different parts of the website, as if you would have searched directly for the
information or as if you would have followed the menu structure. Using the PHPdbRelations
toolkit makes this approach possible and manageable for users.Figure 2
A subproject specific search form
from the website of the “Collaborative Research Centre 574”,
which serves as a portal for information about the scientific goals of the
interdisciplinary projects, the available datasets, members and partners,
and much more. References to publications, presentations, posters, or data
are directly linked to subprojects, as seen in this screenshot. In the
same way those items are linked to people, cruises, or areas—all
relationships are driven by the PHPdbRelations system [17] and served by a
MySQL database [14].


## 4. Data Catalog

Central part of this
project is the geoscientific data catalog. It implies a well-defined
structure, which was built upon the SFB 267 data catalog [23] (also refer to Oncken
et al. [24]). On a location-based level, this structure might be, for example, “Central
American Data”, “Andean Data”, and “Global Data” followed by a structure based
on geoscientific disciplines: cultural and geographical data, geological and
geophysical data (e.g., grav/mag data, active and passive seismological datasets, borehole data, geodetic GPS data, remote sensing and topographic data).Furthermore each dataset
is linked to the people in charge and the related subproject(s). Additionally,
the area is defined by a polygon, which can be queried using the web mapping
solution. The benefit for the user is the possibility to formulate questions
like 	“Which other datasets are available in the region of my interest?” An
online search form enables specific searches for the user. If a single dataset
is selected, further information is provided to characterize the dataset. This
includes title, source, type, format, file size and name, columns, an example
line from the file, producer, processor, access person, subproject responsible
for the dataset, and web links and publications related to this dataset—also
direct web mapping links, if the dataset is published already.ASCII or XML/GML [25]
file formats as clear type formats are highly desired as primary data format, as
they promise the highest long period compatibility. The original data formats
are stored in addition, in our case usually ESRI Shape files, GMT grids, and xyz
tabular files (e.g., csv). At the moment, already more than 100 datasets
are entered into the database; more than 80 can be used for web mapping. Interoperability
in the new IGMAS+ modeling software is achieved through a huge variety of
interfaces and data exchange formats. Special emphasis is placed on an
appropriate XML definition. The software is just under compilation in close
cooperation with European oil and gas industry; so far only internal
information on formats and interfaces are available at a sponsor related
IGMAS-Wiki (Schmidt, pers. comm.).Moreover, we want to
point out that our working group implemented a metadata catalog in contrast to
centralized data(base) storage facilities. Surely, for long-term usability,
the final datasets have to be compiled and published in the last phase of the project
on the website. In the outlook, we will discuss not only the problems but also the
advantages of this MIS-based concept.


## 5. Web Mapping

Web mapping has developed
from providing simple pictures over so called 		“picture maps” to dynamic web
mapping applications. Geosciences represent a diverse field of investigation
and caused by missing standards; many different and quite heterogeneous
solutions for both data and metadata have been introduced but commonly
accepted standards still have to be developed.The Open Geospatial
Consortium (OGC [26]) is supporting this process  for  over ten years now, of
course in cooperation with the International Organization for Standardization
(ISO), in particular with the technical committee 211 (ISO/TC211 [27])
responsible for “Geographic Information/Geomatics”. Among others the OGC
specifications  web coverage service (WCS),  web feature service (WFS) and web mapping service (WMS) are accepted by the majority and hence became standards
for web mapping and exchange between different mapping systems. They provide a
format for distributing features and maps over the internet.As the UMN MapServer is
compliant to the Web Mapping Service (WMS) and the Web Feature Service (WFS)
standards, external datasets from remote hosts—usually other MapServers in
the internet—can be integrated. For example, NASA’s Shuttle Radar Topography
Mission (SRTM [28]) and Moderate Resolution Imaging Spectroradiometer (MODIS)
[29] data was integrated using this technique. Such standards greatly support
interoperability in contrast to monolithic systems and expensive services; for example, data reformatting for transfer from one system to another become needless.Still underway is the
broad application of the ISO19115 standard for metadata characterization and
the corresponding ISO19139 standard for the XML encoding of the metadata in
combination with ISO19119 for proper definition of the service interface worked
out by ISO Technical Committee 211 [27]. At the moment it seems that the
possibility of using custom profiles is a weak point from a data exchange point
of view (following discussion during IDEW workshop [30]).For the SFB web portal, we
integrated the UMN MapServer [4], because the availability of the PHP/Mapscript
[22] interface provides simple and flexible integration. A starting point for
our modifications was the php.mapper framework [31]. A direct connection to the
metadata catalog was implemented; therefore users can search in the catalog
for a dataset using all desired search conditions and add it to the web mapping
menu. This was possible by generating a dynamic map file representation instead
of a predefined, static one.If a dataset is shown in
the map, the user can search for features by a string or query an area to get a
listing of all features inside his selection. In addition to this, it is
possible to query an area and get all datasets from the data catalog not
shown so far that overlap with the selection to find additional information
about a particular area easily.


## 6. 3D-Visualization with a Graphic Wall

The usage of 2D sections
to represent spatially distributed data is often used in geosciences but
cannot be considered as a general solution—features of the original data might be
overseen or in between the arbitrary sections. As real 3D screens, which
produce an object truly in space pixel by pixel, for example, on a series of transparent
and stacked LCD panels, will not exist with sufficient resolution for
geoscientific applications in the near future; the quite old technique of
stereoscopy can help out. Especially considering the improvement of computer
and graphic rendering hardware, a 3D stereoscopic projection system can be
built up nowadays at low cost. In the following paragraph, we describe the
general concept, give decision guidelines, and present our dual system
consisting of a polarizing stereo projection setup and a working-place
autostereoscopic display.The profit to use
advanced visualization for geoscience is indisputable. Only a few years ago,
one had to construct geological bodies (salt domes, subduction zones, etc.)
using foamed or transparent plastics in order to model ideas. Today’s software
tools allow visualization of complicate geometries on the screen and enable the
interpreter/observer to interact with the model through rotation, change of
viewpoint, clipping, hiding of model parts, and/or illumination.The modern interpretation
task in a complex working environment, however, makes higher demands on the
software than just pretty 3D graphics.(1)
The flexible
creation and qualitative or quantitative comparison of different kinds of
maps ease the work with different data types and levels of details.(2)
Easy and intuitive,
interactive input as well as graphical modification of geometry, physical
parameters, and settings of the general project environment—user-friendliness of the graphic—handling is an essential feature of a
software, which will be used by geoscientists usually not familiar with GIS software.(3)
Interoperability is
achieved through a huge variety of interfaces and data exchange formats.
Special emphasis is placed on an appropriate XML definition. As soon as 1D and 2D data
is georeferenced correctly, it can be shown together, for example, with both 3D
topography and bathymetry, or with modeled or measured underground structures, for
example, from density modeling, 3D seismic tomography, or receiver function
analysis.Geosciences have
developed—guided by advanced in computer graphics technology—from 2D map
production on paper toward 3D and even 4D modeling of complex real world
structures. Often, this has led to a lack between academic education in
universities and industrial needs (e.g., in the framework of oil and gas
exploration) induced by historical and financial reasons.


## 7. Technical Realization of Visualization

For stereo visualization,
we use a pair of stacked mainstream DLP data projectors with XGA resolution
(1024 × 768) and 2500 ANSI Lumens brightness, polarizing filters, a 200 × 150 cm
silver screen and polarizing glasses (Figure3). The polarizing filters are
positioned in front of the two-roof-mounted data
projectors. They let transmit the light perpendicular polarized to each other; one
emits just horizontally polarized light, the other just vertically polarized.
The silver-coated screen preserves this polarization states, and hence wearing
polarizing glasses, a channel separation with respect to the left and the
right eye is achieved, and each eye just observes the picture of one-data
projector.Figure 3
The low-cost
3D stereoscopic projection equipment of our working group. Two data
projectors (right side of the figure) deliver two perspective views,
passing perpendicular aligned polarization filters. A reflective-coated
screen (left side) preserves the polarization state of each picture due to
metallic reflection. Viewing through polarizing glasses, each eye just
sees its distinct perspective view, and a stereoscopic depth impression is
the result. Compare the simple sketch in the right upper corner, as it
demonstrates the technical principle of such a Geowall setup [32].The computer system used is based upon an Intel
Core2Duo processor, 2 GB RAM, and a professional Nvidia Quadro FX 4500 graphics
card with 512 MB memory. We have chosen this quite expensive graphics hardware,
as it allows the usage of so-called “Quad-Buffered” stereo mode required by
many professional 3D software products like GoCAD. A 3D mouse from Connexion makes navigation
easier.For preparation and testing of 3D scenes as well as
for single user 3D interpretation, we use an autostereoscopic display of19′′
with a resolution of 2 × 512 × 768 pixels (1024 × 768 pixels standard resolution)
from Dimen Technologies (Figure 4). Recent developments in display technology
resulted in a possible resolution of 2 × 960 × 1080, as 24′′ displays with a normal
resolution of 1920 × 1080 become available on consumer market. Also the
eye-tracking included in such screens is a big step forward, because the user
can move around the 3D monitor and, with appropriate software, even see the
objects from different angles. Without this tracking, movement just leads
perspective distortion and the loss of the correct 3D impression.Figure 4
Autostereoscopic displays use optical elements in front or behind a
standard liquid crystal display (LCD) to deliver a separate picture to
each eye of the user without the need to wear glasses. The figure shows
the bathymetric dataset of the Central American subduction zone, the deep
trench, and the flat shelf area offshore Costa Rica. The screen shown is a
Dimen  C190S without eye tracking—the user must find and hold the correct
viewing position in front of the screen.It is important to point out that two different kinds of
stereo applications exist:normal OpenGL
or Direct3D stereo managed by the driver package of the graphics card
vendor. In normal 2D mode, just one perspective view will be rendered from a
particular scene. In stereo mode, the driver delivers two perspective views
instead: one shifted slightly to the left, another one slightly to the right. Quad-Buffered stereo mode in contrary is
managed by the application itself—for each channel distinct views of the
scene are delivered to the graphics system. Two standard, double-buffered pipes
form a so-called quad-buffered stereo mode. For example, GoCAD,
IGMAS+, Paraview, and Fledermaus  GIS are such applications.


## 8. Case Study: Subduction in Central America

After the introduction to the technical details in the
previous chapters, we will provide insight into the application of the data
management system and demonstrate how to work with the different datasets of
the “Collaborative Research Centre 574, SFB 574” (refer also to the
introduction of the paper). Also the benefit of using
our stereoscopic projection system presented so far will be demonstrated, as we
combine numerous different datasets to gain new insights.Subduction erosion shapes at least half of the world’s
convergent margins. However, the rates and modes as well as spatial and
temporal variation are poorly understood. Based on a compilation of published
and newly derived estimates of subduction erosion along the Central American
margin (Ranero et al. [33], Grevemeyer et al. [34], Bundschuh and Alvarado [35]), we visualize
the geometry of the Central American subduction regarding the pacific Cocos and
Nazca plates below the Caribbean plate.The following figures are snapshots from our 3D
stereoscopic visualization system, and as simple printouts on paper they lose
much of the depth impression. It was a serious task to produce these snapshots,
always trying to get a clear perspective impression. This was done by carefully
choosing the right viewpoint and reducing the number of shown features—compared with the original stereoscopic visualization it is a clear restriction
and underlines the worth of advanced visualization techniques.


## 9. Bathymetry and Land Surface

Figure5 shows
the research area of the Collaborative Research
Center 574 [1] on- and offshore
Central America. The research until 2008 has mainly been focused on Costa Rica
and partly Nicaragua.  The databases behind the images are the SRTM3
topographic dataset [28] with a 90 m resolution and offshore the GEBCO 1-minute
grid [36] with approximately. 3 km grid spacing. Additionally, high-resolution
bathymetry data collected by the SFB 574 and the IFM Geomar have been
integrated.Figure 5
Overview map
of the research area. The SRTM3 topographic dataset [28] and partly high-resolution bathymetry collected by the SFB 574 are combined. The high-resolution bathymetric data point to the dynamics of the tectonic
environments and complex ocean floor bathymetry (Ranero et al. [33, 37]).
The dataset was compiled from several cruises and is owned by the
IfM-Geomar and the SFB 574. Some abbreviations also used in following
figures are introduced: Lago Nicaragua (LN) with the Concepción volcano (CO) in Nicaragua, Nicoya Peninsula
(NP), and Osa Peninsula (OP), both in Costa Rica, now from north to south: Rincón
de la Vieja (RI) and Miravalles (MI) on the
Cordillera Guanacaste (C-G); Arenal (AR) on the Cordillera Tilarán (C-Ti);
Poás (PO), Irazú (IR), and Turrialba (TU) on the Cordillera Central (C-C) and finally the
Cordillera de Talamanca (C-Ta). The Cocos Ridge (CR) collides with Central
America in the southwest. (CP) stands for Cocos plate and (NP) for Nazca
plate.Topography on land is characterized by two prominent
mountain belts: the Cordillera de Talamanca (C-Ta) (southeast) with heights up
to 3800m and the recently active volcanic belt of Costa Rica (Rincón de la
Vieja (RI), Miravalles
(MI), Arenal (AR), Poás (PO), Irazú (IR), Turrialba (TU)). They are members of three mountain ranges,
namely, the Cordillera Guanacaste (C-G), the Cordillera Tilarán (C-Ti), and the
Cordillera Central (C-C).More to the north in Nicaragua, the volcanic
activities show an offset of 50 km eastward. The Concepción volcano (CO) is
located inside the Lago de Nicaragua (LN). Later, the perspective view in Figure11
links the volcano’s geographical  location to crustal domains of low seismic
velocities and therefore to the presence of upcoming magma and fluids inside
the lithosphere.Offshore, active tectonic processes shape the
structure of the  ocean bottom, and manifestations of  fluid venting and sea
mounds  modify the texture of the seafloor from north to south. Seafloor imaging
techniques are the main methods applied in various cruises offshore Central
America (Ranero et al. [37], Klaucke et al. [38]). Multiscale approaches
combined shipboard multibeam bathymetry and backscatter measurements, low- and
high-frequency deep-towed side-scan sonar surveys, video observations, and
recordings of sub-bottom profiler and are well suited to get a rather complete
image of structure and texture of the ocean floor. On its southern part, the Cocos Plate (CP) shows a rough texture covered
by many sea mounds. At a clearly visible border, the bathymetry of this plate
changes abruptly and becomes relatively flat (see also Figure 6). Also the trench
(reaching down to 6000 m depth as indicated by purple colors in the north) changes
at this border. In the southeast the trench not only becomes  significantly
shallower and generally less prominent but also changes its direction, which
is obviously related to the collision of the Cocos Ridge (CR) and the Central
American Land Bridge hosted onto the Caribbean Plate. Huge landslides south of
Nicoya Peninsula mark this change in texture and direction.Figure 6
Perspective
view onto the research area in Central America with some emphasis on the
seafloor bathymetry and the trench. Looking along the trench offshore Central America
in northwestern direction, in addition to the high-resolution SRTM3
topography dataset [28], we use also a lower-resolution ETOPO2v2
topography grid [39]. It surrounds the research area located inside the
red bounding box covering Costa Rica, Nicaragua, and the complex oceanic
floor with the incoming Cocos Ridge from southwest. The area is built by
the northern portion of the Nazca plate in the south, the Cocos plate in
the west, and the Caribbean plate in the east using an exaggeration of 1 : 8.To the northwest in the
outer rise area, however, faulting may rejuvenate hydrothermal circulation by
reactivating and creating new faults, which may breach the sedimentary cover to
allow recharge and discharge of seawater (Grevemeyer et al. [34, 40, 41],
Ivandic et al. [42]). Faults that reach down to mantle depth may facilitate the
migration of water down into the crust and uppermost mantle. Alteration of
crustal and mantle rocks in the trench-outer rise area may therefore affect the
volatile transfer of subduction zones. Refer also to Figure 7, which shows the
ETOPO2 [39] dataset (3 km × 3 km) and horizontal and parallel extension faults
resulting from the ocean floor bending below the continental shelf as an
overlay. Here digitized faults (light
green color) from the geological map of Costa Rica were draped on the low-resolution topography (2′×2′) of the ETOPO2 dataset. It can be seen,
especially in the stereoscopic view of our graphic wall system, that the active
volcanoes are located along a lineament, which extends from the volcano Irazú
to volcano Miravalles. Prominent feature is the lineament (dark pink color),
which separates the Cordillera de Talamanca (southeast in Figure 7) from the
active volcanoes in the northwest. This lineament joins the
margin of the Caribbean plate in the NE and has regional importance, as it is
part of a bigger fault system, which extends from the northern margin of the
Cocos Ridge (CR) toward the Caribbean Plate. Offshore it separates the Cocos
Plate (CP) in the north from the Nazca Plate (NP) in the south.Figure 7
A perspective view from east
along one of Costa Rica's main fault system. It separates the active
volcanoes (east of the dark purple fault line) from the inactive volcanic
Talamanca belt in the south of Costa Rica. The lineament continues to the
southern tip of Nicoya Peninsula and strikes the Cocos Ridge. To visualize
these lineaments, we have chosen lower-resolution topography from 3 × 3 km
ETOPO2v2 data [39].Figure8 (top) shows the Central American topography
seen from west. The dominant peak (exaggeration 1 : 8) is the Irazú volcano. In
the north lays Nicoya Peninsula (NP). The chain of active volcanoes
is separated into a northern and a southern subchain with the Arenal volcano
(AR) in between. The southern chain is built by the edifices of Poás, Irazú, and
Turrialba volcanoes forming the Cordillera Central—the northern one by
Miravalles and Rincon de la Vieja located on the Cordillera Guanacaste.Figure 8
In the upper box the surface of
Costa Rica and the coast near the shelf is viewed from the west using SRTM3
topography data [28]. To the northwest, Lago Nicaragua (LN) is shown in
blue. The geological map of Costa Rica (Tournon and Alvarado [43]) was
draped onto the topography in the lower part of the figure. Intensive red
colors indicate the volcanic arc of Costa Rica with the most active
volcanoes in the circum-pacific margin. The ophiolite complex of the
Nicoya Peninsula is shown in dark green, and sedimentary formations and
rocks are displayed in light and dark yellow tones. Dark blue marks
basalt.In the lower part of Figure8, we draped the geological map of Costa Rica (Tournon and Alvarado [43]) on the
high-resolution SRTM3 grid [28]. The Nicoya Peninsula (NP) consists of uplifted
and eroded seafloor rocks and an ophiolite complex, which crops out in smaller
domains along the Pacific coastal margin of Costa Rica (marked by green
colors). In the south a deep sedimentary basin with a depth of approximately 10 km (Alvarado et. al. [44]) shown in yellow tones is positioned in front of the
older, inactive volcanic arc (purple color). In former times it was also a
target for oil exploration; however no hydrocarbon was found. The Pliocene
volcano chain in the east of the basin runs through Costa Rica from southeast
to northwest just parallel to the quaternary, still active volcanic chain
(shown in red color).On- and offshore gravity data from various
institutions (ICE, Santa Cruz; RECOPE, Santa Cruz; GETECH, Leeds) have been combined into a homogeneous dataset
in Figure9. The wealth of data was recently made available through the data
portal of the SFB 574 as it was described in the first part of the paper. Due
to difficult access to the high mountains, the coverage by gravity observations
remains rather incomplete mainly in the area of southern Costa Rica (Cordillera
de Talamanca, see Figure 7) and eastern Nicaragua. Station complete Bouguer
anomalies, Free-Air anomalies, and isostatic residual anomalies maps were
compiled as a result of the homogenization of gravity field data. Blending the
various gravity anomaly compilations and the geological map of Central America,
we already found correlations between anomalies and geological structures. Dip
curvature analysis of isostatic residual gravity shows that elongate zones of
maximum curvature correspond remarkably well with the structural grain defined
by first-order folds and faults (Figure 7). A comparison with the geological map
(Figure 10) shows a good correlation with the tectonic units and different rock
complexes in most of the region and provides possibilities for crustal
segmentation due to their different rock densities which cause the pattern of positive
and negative gravity field anomalies.Figure 9
The Bouguer anomaly onshore is portrayed
together with Free-Air anomaly (offshore) in the area of Costa Rica and
Nicaragua looking from southeast. Most prominent features are the positive
anomaly on Nicoya Peninsula (NP), which is caused by the high density
ophiolite complex and gravity lows in the basin west of the Talamanca
area. The gravity anomaly is pictured in exact the same area of the high resolution
topography, as presented before in Figure5. For more details refer to the
text.Figure 10
Looking from southeast, we draped
the geological map of Figure8 (bottom) onto the Bouguer gravity map (Free-Air
anomaly offshore and Bouguer anomaly onshore, Figure 9). This combination
provides interesting insight into the “geological” masses that cause the
anomalies of the gravity field. For example, the ophiolite of the Nicoya
complex, forming the Nicoya Peninsula (NP), is located in the area of the
uplifted gravity field map. The active volcanic belt, for example, Irazú (IR) and
Arenal (AR), in this figure is clearly located in a minimum of the Bouguer
gravity field, which points to low densities in the upper crust.Figure 11
Perspective view from the north
into the Central American lithosphere down to a depth of 200 km as it
resulted from receiver function analysis (Dzierma [45, 46]) and seismic
tomography (Dinc-Akdogan et al. [47, 48]). On top of the viewing box the surface
topography on- and offshore is portrayed. The downgoing slab of the Nasca
Plate (yellow color) and some other interfaces of lithospheric boundaries
based on receiver function analysis are presented in the southeastern
region below Costa Rica. Distribution of Vp velocities (at depths of 50,
80, and 100 km) bases on tomographic investigations are presented in the
northwerstern region below the Lago Nicaragua (LN). A low-velocity domain
(orange colors) points to ascending magmatic material, which feeds the
Concepción volcano (CO). For more details refer to the text.In Figure9, we show the
station complete Bouguer gravity as a “flying carpet” over the
topographic data. The coast lines (black) provide a better orientation, and
negative offshore Free-Air gravity anomalies mark the trench dominantly. Both
anomalies and trench disappear in the neighborhood of the Nicoya Peninsula (NP).
Its high-density rocks cause a strong positive anomaly, as it is composed by
old oceanic material and the ophiolite complex (red tones of the gravity
anomaly map. Onshore the gravity lows of the Cordillera Central (C-C) in the
north and the Cordillera Talamanca (C-Ta) in the south are obvious, separated
by the lineament reaching “neutral” gravity anomaly (small band of
green color), roughly following the land crossing fault system already
explained in Figure 7.If the geological map—compare Figure8, lower part—is draped on the
highs and lows of the gravity anomaly map (Figure 9), this combination results in
a rather interesting overlay presented in Figure 10. It is  shown again as a
“flying carped” above the topography.Regarding the
visualization of  surface structures, the possibility to combine datasets with
different resolution in various ways always with exact spatial relationship to each
other is a clear advantage of this system. Especially advanced methods of
combining datasets like  draping geology or gravity onto topography deliver
fruitful new insights into complex problems.


## 10. Subsurface Modeling and Visualization

In the following part we
will focus on the underground structures, which result from active and passive
seismic studies, remote sensing techniques, and joint density modeling of datasets, which were compiled by members of SFB 574/subproject A2.Figure11 shows results of seismological studies. The
subduction slab (southeast, below Costa Rica) was compiled from a 3D tomography
study in the upper part of the lithosphere (blue color) and receiver function
analysis in the lower part of the image (yellow color). The angle of
subduction appears steeper than expected due to exaggeration. For better
orientation we added horizontal planes (light grey colors) in depths of 50,
100, 150, and 200 km. In the northwest, 3D tomography results below the Lage de
Nicaragua (LN) are shown.In Costa Rica, the
principal underground structure in a “subduction factory”, the subduction
slab, has been composed by 3D seismic tomography results at shallower depths
down to approximately. 70 km (Dinc-Akdogan et al. [48], Dzierma et al. [45]). With the aid of receiver
functions analysis, the slab can be modeled even deeper than 150 km. In these
studies a steep subduction angle of ~60° is observed, which is significantly
different to the slab inclination of 45° proposed in literature so far (Dzierma
et al. [45], Dzierma [46]).Additionally, in
Nicaragua, the 3D tomography modeling bears exiting insights in the volcanic
system of Central America; a chimney-like structure originating from a depth of
approx. 100 km is located exactly beneath the Concepción volcano (CO) in the Lago
de Nicaragua (LN). The orange tones mark domains of low Vp values, and obviously
this new observation reflects the existence of “hot” magmatic
material—at least a higher content of fluids—in depths between the Earth's
surface and the depth of 100 km.To verify the geometry of
the modeled slab, the seismological events (earthquakes hypocenters) received
from local seismological networks during six monthes have been integrated into
Figure12. As expected, they verify the model geometry and are mainly positioned
onto the proposed slab geometry. The different colors of the small
“balls” indicate the depths. Again, the “chimney”, already
visualized in Figure 11, is shown here in the perspective view and in relations
to the colored hypocenters. It leaves the slab from a depth of approximately. 100 km
and leads   to the volcanic chain with a slope of ~45°. In the interpretations of
Dink-Akdogan [48] and Dzierma [46], this structure is related with fluid pathways
driving induced melting and hence triggering volcanic activity.Figure 12
Looking roughly from southeast along
the subduction zone with the slab below Costa Rica, the earthquake
hypocenters from local networks of SFB 574 subproject A2 for a 6-month
period are shown as balls. Not only  are they distributed on the modeled slab but
also they form an approximately.45°  channel in direction to the volcanic chain. The
red-bordered gray surfaces are 50 km separated from each other for
orientation in space.Using our in-house modeling software IGMAS, a 3D
density model (Figure13) could be compiled in the area of Central America,
taking into account various results and models of seismic research (Figures 11  and  12) as constraining information about the principal slab geometry (Dzierma
[46], Dzierma et al. [45], Dinc-Akdogan et al. [48], Thorwart, pers. comm.). Evenmore,
for the first time a 3D density model has been accomplished (Lücke [12], see
Figure 14) by combining the results of curvature analysis and Euler deconvolution
together with other constraining data from geological maps covering
the surface of the model, structural information from older seismic profiles
and earthquake hypocenters. Both models are presented in the
next paragraphs.Figure 13
The 3D density model is compiled
by the IGMAS software [6, 7]. It is constrained by the seismological
information displayed in Figures 11 and  12. The model is seen from the
southeast together with the hypocenters and the DEM as surface. The model dips down reaching
a depth of 200 km. It was mainly compiled by V. Giszas.Figure 14
A second model was compiled by
Lücke [12] and aimed to model the upper crustal density domains in the
area of the active volcanic arc of Costa Rica. The structure in the center
(red color) causes the gravity deficit beneath the volcanic arc. The
depth-coded “points” (from blue to white) represent the source points of Euler
deconvolution (Pašteka [51]). They are calculated
independently from the gravity modeling and can help constraining the 3D
model.In collaboration with the
seismological research group (subproject A2 of the SFB 574), the new tomographic
results were taken to constrain the larger, regional model of Central America.
Velocities were converted into densities following an approved method of
Sobolev and Babeyko [49] (see also Hacker and Abers [50]) and assuming typical
gradients of temperature and pressure conditions in volcanic areas. Therefore, the 3D density model provides a synoptic
picture of the investigated area down to the upper mantle. It can help to
identify the border between larger tectonic blocks—for example, the Chortis block in
the north or the Chorotega block in the south. The modeling was used to
visualize the gravity effects due to serpentinization of oceanic lithosphere at
the Pacific side.At a more local scale,
our 3D modeling provides insight into the upper crustal parts under the
volcanoes of Central Costa Rica. Surprisingly, the area of the central volcanic
chain in Costa Rica is covered by negative Bouguer anomalies, whereas further to
the north the volcanic chain is located in an area with positive anomalies.
This suggests a different composition of crust, that causes regional density
anomalies in both areas. This should also be reflected by different seismic
velocities.In combination with the
regional model (Figure13), also a quite local and shallow density model of Costa
Rica (presented in Figure 14) has been modeled using lGMAS gravity modeling
software (Lücke [12]). It is presented together with solutions from Euler
deconvolution analysis (Pašteka [51]). This model
consists of 3 main bodies: the red one belongs to the active volcanic chain
mentioned before, whereas the two bodies along both sides (gray and light red)
reflect gravity anomalies following inactive pale arcs laying west and east,
respectively.Using Euler deconvolution, this shallow gravity model
could be constrained to source depths of density anomalies in the lithosphere. For this kind of three-dimensional point distribution,
the stereographic visualization method can lead to new insights, as the
complexity can be really “seen”. The
process of finding clusters and tracing them down to improve model geometry can
be achieved much better than using the classical approach of vertical profiles
showing just projections of 3D features.In Figure15  the results of seismic modeling from
receiver function analysis and tomography are combined with the modeled
“local” density structures of Lücke [12] (shifted up 20 km over
surface level). An interesting aspect can
be visualized here: Lücke's modeled “volcanic root” is placed right
exactly over a thickened crust above the Mohorovičić discontinuity
(grey surface from receiver function analysis). The thickened crust is shown by the light pink upwelling surface. One may
speculate that this updomed structure is also related to magmatic processes
and reflects interactions between the recent volcanic arc and lower
crustal/upper mantle magmatic reservoirs.Figure 15
A perspective view of the
geophysical interfaces compiled from seismic and gravity modeling from
east. On top, the Bouguer gravity field is displayed, shifted up 20 km
together with bodies from Lücke’s local density model. Below, the
down-dipping plate and other interlithospheric interfaces of the Central
American crust-mantle system from 3D tomography and receiver function
analysis are shown. They were displayed for joint interpretation at our
Geowall [32].Especially for
underground structures, where the depth information is more than just one more
attribute, stereoscopic visualization brings realistic geometric relationships.
Modeled bodies, surfaces, lineaments, and point datasets can be drawn into the
third dimension and do not  “fall back” onto a sheet of paper. Unfortunately for
the reader, we had to replace this by color-coded
depth in most figures.


## 11. Outlook

The big task to improve efficiency in geodata
management is the broad application of general accepted standards. XML-based
frameworks like, for example, the Geography Markup Language (GML [25]) are already used
widely and replace storage in raw data files. As such structures are using
clear text representation in conjunction with carefully named XML tags, they
might be partly self-explaining to future users—in contrast to pure number
tables or even binary files.Using techniques like OGC’s WMS/WFS/WCS, it is possible
to build up a network of geodatabases. Management and access can be
distributed, so scientists can concentrate on interpretation and
interdisciplinary cooperation instead of juggling around with different data
sources, formats, and projections. The “borders” between different GIS
solutions, sometimes even introduced by intention out of commercial interests,
can be vanished by building them against general accepted formal standards, if
these standards become strict enough regardless of multidisciplinary context.Meetings to define the current status of (meta)data
standardization and further needs to improve global data exchange like the
“International Data Exchange Workshop” (IDEW [30]) can help to further improve
and implement already well-prepared standards.In contrast to the presented metadata catalog
describing datasets not harmonized in general, several projects aim to collect,
store, and harmonize all available data right from the beginning in a
centralized database driven GIS storage system (Thomsen, pers. comm.,
Schirnick, pers. comm.). The work flow acquiring, managing, and processing data
could be more structured, as such systems will not just be used as data
storage for final datasets but replace locally saved files at all working
stages. Versioning capabilities will avoid data loss and allow to check every
single processing step. Probably most important, filling a metadata catalog
no longer represents deterrent overhead but is carried out inherent by the
system, as it just accepts datasets with a proper metadata definition.Considering the web mapping at present, a free 3D GIS
visualization should replace the 2D cartographic web mapping available nowadays
to truly visualize 3D structures over the World Wide Web. This can be realized
for case studies using Shockwave or similar technologies but a general
approach including standard protocols should be initiated to overcome the
restrictions of the image delivery approach. In this context, also
object-oriented database systems using a standard for 3D models or at least
common interfaces for exchange of data are required.The presented 3D stereoscopic visualization system is
a great tool for interpretational tasks. It is a great advantage to see depth
information realistically and use color and brightness for additional
information. Especially, point and line data become visible in space. The
technique of using cutting surfaces and project data onto such 2D elements
distorts true 3D recorded datasets. Usage of shadows to achieve a perspective
impression is also limited and reduces the usability of colors and the level
detail. A 3D visualization system can represent more parameters more realistically
at the same time.The system presented in this paper is a low-cost
geographic wall. For visualization, improvements to the projection system could
be advanced data projectors with increased resolution (1920 × 1080) and
brightness (>3000 ANSI Lumens). Also other filter systems for the
stereoscopic projection could result in better channel separation and usability
(e.g., Infitec filters do not base on
polarization but on a spectral band pass). The combination of several screens
to one, surrounding the viewer by270°, or the use of a spherical screen with
special optical lenses would bring our one screen projection system nearer to
industry-level 3D caves, where more information can be shown to the
investigating scientists at the same time. Also head mounted displays (HMDs)
could become an option for joint interpretation. Using one projection system,
just one perspective can be calculated at one time. If every user would wear an
HMD, a personal view (based on the tracked location of the person in the room)
could be calculated. More people could walk around the “virtual” model in the
middle of the room, and everybody would see the particular aspect of the model.Regarding the user interaction, devices like head
tracker or cyber gloves can be combined to let the scientist touch and
naturally move or rotate objects. The head tracking system would give the
scientist a very realistic impression of the objects, as the perspective is
calculated according to his or her position. With a hand control unit (cyber
glove), it would be possible to control the virtual universe in a natural,
rapid way. Models could be moved, rotated, or sliced easily. In contrast to the
head tracking system, which is compatible to most scientific software products,
the cyber glove needs special interfaces to interact with software. Our new
in-house product IGMAS+ will be compatible to both systems. Both approaches not
only lead to a more realistic “virtual” reality in 3D but also and more
important turn a cinema-like 3D visualization project into a tool with
user-friendly, rapid, realistic, and natural control.


## 12. Conclusion

The management of complex, diverse, and sometimes huge
amounts of geoscientific data is not just a question of storage. The usage of
metadata and the connection to dynamic mapping makes it possible in particular
for scientists working in an interdisciplinary research environment not just to
manage their own data but also to undertake joint interpretation by
integrating data from other geoscientific methods as problems become complex.The metadata catalog presented here is capable of
managing diverse datasets and presenting them in a structured form to the
internet audience. The level of website internal linking is tremendously
increased, giving the user the best chance to find what he is interested in.
Nevertheless a particular type of content is always presented inside its own
context. Especially the possibility of supporting or even initiating
cooperation with researchers outside this research project is one of the
biggest aims. It is also possible for local institutions and agencies from
Central America not only to see available data from this project but moreover
to insert also their (meta)data to complete the collection and hence
implement a central data portal. As the data is not available for download
usually, the person in charge of the dataset can be contacted. So
misinterpretation of data can be avoided and cooperation supported in contrast
to a pure download link. Of course, in the final period of the Collaborative
Research Center’s work, a compilation of datasets must be prepared to guarantee
long-term availability of the results.The presented case study
brings together datasets from different geoscientific disciplines, some are
distributed in space, some on vertical sections and others just define a
position, for example, volcanoes on the surface. By georeferencing them, they become
comparable, not just qualitatively but also quantitatively.As it is not possible to
bring the stereoscopic depth impression to the reader of this printed journal,
the difference between “guessing” the depth structure by turning around a model
in a 3D data viewing software and the effect of really “see” the separation of
objects along the viewing axis must be experienced and surely aid to the
understanding of complex spatial relationships.As many features are
presented simultaneously to the audience, stereographic visualization brings
more clarity or, let us say, more “space”. In a
collaborative research environment, this can be a catalysator for joint
interpretation and critical analysis of results taking into account diverse
other datasets otherwise probably just considered in a more or less qualitative
way.The used system is,
unlike systems many  years ago, based entirely on mainstream hardware. It works
together with either Linux or Windows and is compatible to many available
software products developed in the last years. Because programming languages
like C++ or JAVA have already implemented the rudimentary routines into their
3D visualization classes, it is  usually a simple task to enable stereoscopic
visualization from recent 3D geoscientific software
products.



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*Source: 878324-2009-06-02.xml*