ArcGMT: a suite of tools for conversion between Arc/INFO® and Generic Mapping Tools (GMT)

ARCGMT: A SUITE OF TOOLS FOR CONVERSION BETWEEN

ARC/INFO1 AND GENERIC MAPPING TOOLS (GMT)

DAWN WRIGHT,1* RAY WOOD,2 and BRENDAN SYLVANDER3

1Department of Geosciences, Oregon State University, Corvallis, OR 97331; 2Institute of Geologicaland Nuclear Sciences Ltd., P.O. Box 30-368, Lower Hutt, New Zealand, and 3College of Oceanic and

Atmospheric Sciences, Oregon State University, Corvallis, OR 97331

(Received 24 October 1997; revised 27 March 1998)

AbstractÐArcGMT is a new suite of tools for converting Generic Mapping Tool (GMT) grids to a for-mat readable by the Arc/INFO1 and ArcView1 geographic information system (GIS) packages and,conversely, for creating GMT grids and ®les from Arc/INFO formats. GMT has arisen as an uno�cialstandard among geoscientists for producing maps, particularly from marine bathymetry, sidescan sonarimagery, gravity and magnetics data. Many geoscientists have also turned to the mapping, databasemanagement and spatial analytical capabilities of Arc/INFO and ArcView. Subsequently, a need hasarisen, particularly in the marine geology and geophysics community, for a conversion interfacebetween these two environments. This initial version of ArcGMT is designed for UNIX-based worksta-tions running Arc/INFO version 7.0 or higher and GMT version 3.0 or higher. ArcGMT consists of aseries of UNIX shell scripts and Arc Macro Language (AML) ®les, bundled in an easy-to-use menuinterface for use within Arc/INFO. Also described is a `beta' prototype of ArcGMT, still under devel-opment, that functions as an extension to ArcView version 3.0 with Spatial Analyst. # 1998 ElsevierScience Ltd. All rights reserved

Code available at http://www.iamg.org/CGEditor/index.htm

Key Words: Data conversion, Geographic information system (GIS), Marine geology, Geophysics,Physical geography.

INTRODUCTION

In recent years scores of geoscientists have turnedto the geographic information system (GIS) for

advanced mapping and managing of their data, aswell as for integration with other types of environ-

mental data (Wadge, 1992a,b; Walker and others,1996). This is particularly true in the marine ge-

ology and geophysics community (Fox, Bobbitt andWright, 1996; Wright, 1996; Bobbitt and others,

1997; Hatcher, Mayer and Orange, 1997; Wrightand Goodchild, 1997) where scientists also rely

heavily on the Generic Mapping Tools (GMT)package. GMT has arisen as an uno�cial standard

for producing maps of marine bathymetry, sidescansonar imagery, gravity and magnetics. On the GIS

front, many have turned to Arc/INFO1 and itssmaller desktop cousin, ArcView1, both of the

Environmental Systems Research Institute. Arc/INFO and ArcView are now considered to be two

of the world's leading vector GIS packages (GISWorld, 1996) and have been adopted in full by

agencies such as the USGS and NOAA, as well asuniversity labs and classrooms throughout the

Western hemisphere. A need has risen, once again,

particularly in the marine geology and geophysics

community, for an interface between these heavily

used software packages. GMT is often used to pro-

cess and create base maps but provides little means

for the incorporation of detailed attributes to the

locations that are mapped out. Arc/INFO and

ArcView, as GIS packages, provide a combination

of mapping and relational database capabilities that

exceeds GMT. However, the base maps that are

more readily created in GMT (in concert with the

MB-System package of the Lamont-Doherty Earth

Observatory, which processes raw multibeam bathy-

metry and high resolution sidescan) provide a cru-

cial base layer for many applications that are

desirable for the GIS. An example is the ®ne-scale

mapping of hydrothermal vent locations, animal

communities and lava ¯ows at sea¯oor-spreading

centers, a task that is only05% complete on a glo-

bal scale (e.g. Haymon and others, 1991; Embley

and others, 1995). Recently, with the increased

popularity of GIS, shipboard data acquisition en-

vironments have been set up to import data from

submersibles or remotely-operated vehicles directly

into a GIS (Wright, 1994, 1996; Bobbitt, 1996;

Bobbitt, Fox and Wright, 1996), some in real time

(Hatcher, Maher and Orange, 1997). This has

greatly facilitated the integration of geologic obser-

Computers & Geosciences Vol. 24, No. 8, pp. 737±744, 1998# 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain0098-3004/98 $ - see front matterPII: S0098-3004(98)00067-3

*Corresponding author. Fax: +1-541-737-1200; E-mail:[email protected].

737

vations with vent chemistry and biology. However,bathymetry or sidescan sonar imagery, which allow

for the interpretation of larger geologic structuresthat put these ®ne-scale observations in regionalcontext are most often collected, processed and

archived in GMT grids. This usually occurs on sep-arate expeditions preceding the submersible or ve-hicle dives. It is crucial to be able to add these data

as base themes or layers to the existing GIS data-bases. Conversely, it may be necessary to exportfeatures mapped in the GIS for inclusion in elabor-

ate GMT maps and plots.Here we present ArcGMT, a suite of tools for

converting GMT grids to a format readable by Arc/INFO and ArcView. ArcGMT will also create

GMT grids and ®les from Arc/INFO format. Webegin by providing brief overviews of GMT, Arc/INFO and ArcView, followed by a functional

description of ArcGMT.

GMT

GMT is a public-domain software package fordata manipulation and generation of high-qualitymaps and scienti®c illustrations. The initial version

was released in October of 1991 (Wessel and Smith,1991) and re-released in a much-improved version 3in 1995 (Wessel and Smith, 1995). An electronic

survey by Wessel and Smith in 1994, as well as anassessment of ftp tra�c and submitted registrationforms, reveal that more than 5000 users worldwidefrequently use GMT in their work. Within the mar-

ine geology and geophysics community, GMT iscurrently in use by scientists on all continents,aboard research vessels in the University National

Oceanographic Laboratory System (UNOLS) ¯eetand even aboard U.S. Navy submarines and aircrafton scienti®c missions.

GMT runs on almost all computer platforms thatare capable of running UNIX2, from Cray super-computers to workstations to PCs andMacintoshes. Although it is capable of ®ltering and

gridding 1- and 2-dimensional data sets, GMT isbest known and used for its advanced plotting andcartographic capabilities (Fig. 1).

ARC/INFO1 AND ARCVIEW1

With estimated sales of more than $200 million

(Daratech Inc., 1994), the Environmental SystemsResearch Institute is the world's largest GIS com-pany. It provides stand-alone software in product

categories ranging from desktop GIS to high-end,advanced analytical GIS to software developmenttool kits. The company's ¯agship product, ARC/

INFO, is the most frequently used GIS in a varietyof market and scienti®c research segments, mostnotably petroleum and mining, groundwater map-ping, geologic mapping and marine geology. In ad-

dition, ArcView, the company's new desktop GIS,has been successful and provides an easier-to-use,

cost-e�ective addition to ARC/INFO.GIS packages such as Arc/INFO and ArcView pro-

vide not only an e�cient means for mapping and plot-

ting data but also for archiving, manipulating andanalyzing data in relation to other layers or themes ofobservations. Four characteristics that distinguish

GIS frommapping packages such as GMT are:(1) Provision of linkages within a relational data-

base management environment between the lo-

cations of points, lines, areas and/or grids anddetailed descriptive information about them (attri-butes), along with associated metadata.(2) Provision of algorithms for the spatial analysis

of data (e.g. spatial autocorrelation, advection anddispersion modeling, pattern recognition and analy-sis, bu�ering, spatial interpolation, overlay, etc.).

(3) `Spatial intelligence' or the ability not only tochange map projections but also subsequently tocompute distances, identify nearest neighbors, cal-

culate regions of proximity around existing featuresand update their attributes accordingly.(4) Provision of a digitizing interface for direct

input of geographic coordinates from paper maps.

FUNCTIONAL DESCRIPTION OF ARCGMT

ArcGMT allows users to take advantage of thecapabilities of both GMT and Arc/INFO by pro-

viding a means for data conversion between the twoenvironments. This initial version is suited only forUNIX-based workstations that are running Arc/

INFO version 7.0 or higher and GMT version 3.0or higher. ArcGMT consists of a series of UNIXshell scripts and Arc Macro Language (AML) ®les.AML is the language used in Arc/INFO to pro-

gram and tailor the environment.Within the Arc/INFO environment ArcGMT is

operated through a simple pull-down menu from

which the user may select documentation or choosefrom three types of conversion:(1) GMT grids are converted to Arc/INFO grids

by writing the binary GMT to an ASCII ®le andthen reformatting the ®le to space-delimited row-major order and with header information needed byArc/INFO, including cell size, number of rows and

columns and coordinates of the grid's lower-leftcorner. The ®le is then piped to the Arc/INFOASCIIGRID command for conversion to an Arc/

INFO grid.(2) Arc/INFO grids are converted to GMT grids

by ®rst changing the grid (a raster data structure)

to a vector point coverage. A coverage is Arc/INFO's primary method for storing point, line andareal geographic features. Structurally, the coverage

is a directory containing binary ®les that store thelocational coordinates (`Arc') and ASCII database®les that store the locations' attributes and topology(`INFO'). Arc/INFO coverages and grids can also

D. Wright, R. Wood and B. Sylvander738

be read by ArcView. The initial change from a grid to

a point coverage is necessary because each cell in an

Arc/INFO grid is given a value (e.g. depth or el-

evation) corresponding to an x±y location on the sur-

face of the earth, but location is inherent in the

storage structure and not explicitly de®ned as an attri-

bute. A point coverage derived from a grid, however,

explicitly de®ne z-coordinates as an attribute.

(3) Arc/INFO coverages may also be converted

to text ®les in a format readable by GMT scripts.

This would be appropriate for features digitized in

Arc/INFO, such as the outlines of lava ¯ows or

fault lineations, that would need to be included in a

GMT plotting script. ArcGMT prompts the user

for an existing Arc/INFO line or polygon coverage,

converts it to a text ®le and then formats it for

GMT. Points may just as easily be mapped byGMT with little or no conversion.

ArcGMT with ArcView: A prototype still underdevelopment

ArcView was introduced in 1994 as a scaled-down, desktop GIS, with a graphical user interface

not available in Arc/INFO, thereby allowing theuser to visualize, explore and query data moreeasily. With a learning curve of 1±5 days (versus 6±

12 months for Arc/INFO) many geoscientists haveturned to ArcView as their primary introduction tothe world of GIS. Most users of GMT who are alsoversed in GIS have installations of Arc/INFO,

Figure 1. Example of advanced cartographic capabilities of Generic Mapping Tools (GMT). Composite®gure showing 3D mesh of Hawaiian topography from ETOPO 5 bathymetry on top of contour map

of Hawaiian geoid. After Wessel and Smith (1991).

ArcGMT: a suite of tools for conversion between Arc/INFO and Generic Mapping Tools (GMT) 739

although a growing number of them are turning to

ArcView as well. Recent revisions to ArcView have

included more powerful spatial analytical capabili-

ties, although Arc/INFO remains the full-service,

industry-standard GIS toolkit. The ArcView code

for ArcGMT is a prototype still under development,

but is o�ered here for advanced users of ArcView

who are totally unfamiliar with Arc/INFO. The

ArcView prototype (written in Avenue, the pro-

gramming language of ArcView) allows users to

make the same conversions as within the Arc/INFO

environment, but it should be noted that the pre-

sent method is not as streamlined. ArcGMT conver-

sions within the ArcView environment are

dependent upon the implementation of remote pro-

cedure calls (RPCs) between Arc/INFO and

ArcView. There are several forms of RPC, but both

ArcView and ARC/INFO use the Open Network

Computing standard. RPCs allow client appli-

cations to initiate procedures in a server application

across a network. UNIX RPC servers are uniquely

identi®ed by a hostname, a server id and a version

number. An RPC client application uses this infor-

mation to establish the RPC connection. In

Fig. 2(A). Caption on later page.


Fig. 2(B). Caption on next page.


ArcGMT, ArcView makes client requests to anArc/INFO server in the form of Avenue statements.

These statements call the ArcGMT conversionAMLs and shell scripts and then allows the user toimport the results into the ArcView environment.

Before using ArcGMT within ArcView, the usermust start Arc/INFO as a server with a simple àndtype [iacopen]' directive and then start ArcView.

Using ArcGMT with ArcView requires theArcGMT extension (àrcgmt.avx'). Extensions are

add-on programs to ArcView (written in Avenue)that provide additional functionality. When anextension is loaded, ArcView's graphical user inter-

face changes to re¯ect this added functionality inthe form of additional menu items, buttons and/or

tools (ArcView tools are distinguished fromArcView buttons in that the user must go beyond amouse click and perform an action with the cursor

in order to get a result). The ArcGMT extension

adds the following functionality to the ArcView

interface:

* Buttons to perform the three conversions

described above, as well as clip out subsets of grids

to create new grids and create hillshaded themes

from grids.

* A tool to create an empty grid based on a rec-

tangle drawn by the user and the user's speci®cation

of row and column numbers.

* A menu item (under the `Theme' heading in

when a View is active) to convert an ArcView sha-

pe®le (the native ArcView data format) to an Arc/

INFO text ®le.

ArcGMT also comes with an optional ArcGMT

project ®le (àrcgmt.apr') that automatically opens

ArcView with the extension already loaded.

Figure 2. Results of GMT to Arc/INFO grid conversion and vice-versa in ArcGMT. (A) GMT contourmap of GMT grid of Sea Beam 2000 bathymetry from SW Paci®c, input to ArcGMT for conversion.Data are from Wright and others (1996). Stars on map show where rocks were dredged from atop thisseamount. (B) Screen dump from ArcGMT session, showing same grid after conversion to Arc/INFOformat. Grid is displayed in default grayscale within GRID module of Arc/INFO. (C) 1-degree,1:250,000 USGS DEM in Arc/INFO format, displayed in default grayscale within GRID module ofArc/INFO. Data are from USGS Eros Data Center web site (http://edcwww.cr.usgs.gov/glis/ hyper/guide/1_dgr_dem). (D) Contour map created in GMT of resulting GMT grid (100 m contours, anno-

tated every 500 m).


RESULTS AND CONCLUSION

Figure 2(A) and (B) show the result of a GMT to

Arc/INFO grid conversion in ArcGMT. The orig-

inal grid was of Sea Beam 2000 bathymetry reveal-

ing a seamount in the SW Paci®c discovered in

May of 1996 (Wright and Bloomer, 1996). Grid

cells were not square due to the gridding algorithm

Figure 3. GMT contour map of GMT grid of Sea Beam bathymetry from NE Paci®c, overlain withfault lineations (heavy lines) that were exported from Arc/INFO line coverage by ArcGMT. Data arefrom RIDGE Multibeam Synthesis web site (http://imager.ldeo.columbia.edu/ ridgembs/ne_pac/html/

home.html). Contour interval is 250 m, annotated every 1000 m.


used when the grid was created with MB-Systembut ArcGMT was still able to make a perfect con-

version. Figure 3 shows a GMT map of Sea Beambathymetry overlain with fault lineations that wereexported from an Arc/INFO line coverage with

ArcGMT. Figure 2(C) and (D) show the results ofan Arc/INFO to GMT grid conversion inArcGMT. The original grid was a 1-degree (3-by-3-

arc-second data spacing), 1:250,000 USGS DigitalElevation Model (DEM) of the Big Island ofHawaii downloaded from the USGS Eros Data

Center (http://edcwww.cr.usgs.gov/glis/hyper/guide/1_dgr_dem).A few cautions apply to Arc/INFO to GMT grid

conversions in ArcGMT. The conversion is

designed primarily for elevation or bathymetry datain units of positive m. If the user tries to convertanother kind of grid (e.g. gravity in mgals), the z

value may be o� by one to two orders of magni-tude, which can easily be remedied with `grdmath'in GMT. USGS DEMs may be in x±y units of deci-

mal seconds, which are unacceptable units forGMT. Before converting, the user should alwaysdoublecheck the characteristics of the grid with the

DESCRIBE command in Arc/INFO. The gridbounds output by DESCRIBE should be noted bythe user for answering prompts in ArcGMT. It maybe necessary to project the units of the grid to deci-

mal degrees and/or to make a datum transform-ation. In the case of the USGS DEM of Hawaii,the original WGS72 datum was changed to match a

database stored in NAD83 with the following sub-commands in Arc/INFO PROJECT: output, projec-tion geographic, units dd, datum nar_d three,

parameters, end. Such a three-parameter transform-ation may result in errors or uncertainty in theorder of050 m.Future improvements to ArcGMT include

improvements to the Avenue scripting for theArcView prototype and a re-release of the extensionso that novice, as well as advanced users of ArcView

will be able to use ArcGMT. Additional Avenuescripting will also be needed to automatically readthe hostname of the Arc/INFO server for the

ArcView extension `arcgmt.avx.' Also desirable is ad-ditional code for both the Arc/INFO and ArcViewenvironments that will allow users to interactively

test projections, datum transformations and variousgridding intervals before converting grids from Arcto GMT. Source code and a help ®le for ArcGMTare available from the primary author's anonymous

ftp site (ftp://dusk.geo.orst.edu/pub), as well as theComputers & Geosciences Editorial web page(http://www.nrcan.gc.ca/gsc/iamg/cghome.html).

AcknowledgmentsÐThis work is supported by theNational Science Foundation under grant OCE-9521039.The paper was improved by the comments of twoanonymous referees.

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ArcGMT: a suite of tools for conversion between Arc/INFO® and Generic Mapping Tools (GMT)

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