GSMCAD is a Microsoft Windows program designed specifically for field and office compilation of geologic maps. It was developed by the U.S. Geological Survey for in-house use and is made available to the general public for a nominal charge as Open-file report 96-007. It can also be downloaded for free on the internet at URL http:/ncgmp.cr.usgs.gov/ncgmp/gsmcad/gsmcwww.htm. Documentation is in the form of a Windows help file, GSMCAD.HLP.
Line and point data can be entered from a digitizing tablet, by drawing on screen with a mouse, by reading in a table or DXF file, and by connecting to a GPS (global positioning satellite) radio receiver. The maps and drawings created can be plotted on an inkjet or a pen plotter, printed on any MS Windows-compatible printer, or exported to DXF files or Arc/Info coverages.
The program is designed to be efficient to use, easy to learn, and require minimal special equipment. It allows Arc/Info coverages to be created and color geologic maps produced from Arc/Info without the user having to be trained in the use of the Arc/Info program.
A primary goal in development of GSMCAD is to maximize productivity by simplifying procedures and minimizing unnecessary keystrokes, mouse movements, or body movements. The second goal is to minimize training time and mistakes by making the program intuitive and easy to learn, supplying comprehensive and context sensitive on-line help, and conforming to a layout similar to popular Windows and drafting programs. The third goal is to empower the field geologist and recruit him to join in digital data production by providing an easy and comprehensible way to create and control his own digital data without extensive recourse to "GIS experts". This must be done in such a way that the results will still meet quality standards and be available in industry-standard formats such as DXF and Arc/Info coverages. A fourth goal is to speed production and accuracy and minimize repeated trips to the same area by enabling the geologist to digitally collect point and line data and compile his map in the field. The fifth goal is to keep things simple so as to minimize the expense of equipment needed to run the program.
There are many possible techniques for digital compilation of geologic data into GIS data sets, and powerful commercial software at reasonable prices is increasingly available. Under what circumstances might GSMCAD still be a useful additional tool?
The most likely benefit is in situations where speed, simplicity, and economy are necessary, and resources are limited. Possible examples are as follows:
GSMCAD can be used in combination with a GPS receiver for data collection in the field in two modes. In situations where most observations are made from a vehicle a GPS receiver outputting NMEA (National Marine Electronics Association standard for navigational data) $GPGGA sentences can be connected directly to the serial port on a laptop running GSMCAD. When the <GPS cursor> option under the DISPLAY menu is toggled on, the GPS position will drive the screen cursor just as the mouse or digitizer puck would. Observation points can be digitized with a keystroke. The points are linked either to notes typed into a text file on the spot, a table of values, structure symbols having azimuth and inclination attributes (such as strike and dip), or digital photographs. When the GPS cursor reaches the side of the screen window, the window will redraw centered on the current position.
A second mode is less "high-tech" but more practical. Observations are recorded in a simple field book as the positions are recorded as waypoints in the memory of the GPS receiver. At the end of the day the GPS unit is connected to the laptop and the day's waypoint coordinates are downloaded into a file that is subsequently read to generate observation points in the GSMCAD database. The station number from the fieldbook is an attribute of those points so they can be linked to data copied in from the fieldbook. In the future it may be possible to download files entered on the outcrop in a palm-size computer instead of in a fieldbook (such as Fieldlogger files on an Apple Newton).
Both methods work best if a preliminary map is digitized and printed over a basemap before going to the field. Lines sketched on the map or on airphotos in the field can be transferred to the database by digitizing on screen with the mouse, by reference to pre-existing digitized lines and GPS points. A digital orthophotoquad (DOQ) or vectorized basemap can be displayed behind the map vectors to guide line placement. At present digital raster graphics (DRG) cannot be displayed. If digital bases are not available, the same result can be achieved by taking a small or roll-up digitizer to the field.
The following partial list summarizes some of the capabilities and characteristics of the GSMCAD program.
New geodetic (lat, lon) databases corresponding to standard USGS series maps are quickly and simply created by specifying the type of map and entering coordinates for the northwest corner. An outline frame or grid of lines is automatically created. The program determines the projection parameters of the base map and stores them in a projection file. A preliminary plot file is generated listing the definition and plotting characteristics of the most common entities on geologic maps. Unusual projections and map outlines are also supported but require more user input. Projections supported include Mercator, Universal Transverse Mercator (UTM), Transverse Mercator, Oblique Mercator, Lambert Conformal Conic, Albers Equal Area, Equidistant Conic, and Polyconic. Cartesian databases in ground meters for cross sections and inches for correlation diagrams are also easily generated.
All GSMCAD entities have three numeric attributes (CODE, P1, P2) stored in the database. Other attributes may be stored in associated lookup files. Before any entity can be created the three basic attributes must be entered (or continued from the previous entry). The first attribute (CODE) is linked in the plot file to a description of what that code represents, such as "thrust fault, certain" or "bedding attitude symbol." A pull-down menu listing the code next to the description allows the user to select the geologic feature to be represented without having to remember the code. Defining the entities from the manuscript map as they are entered is more efficient than classifying the spaghetti bowl of unclassified lines that sometimes results from scanning.
Attributed polygons can be created from lines and label points in a GSMCAD database using the GSMPBLD program (Selner and Taylor, 1993), but that step is done more easily in Arc/Info. The polygons to be created are attributed in GSMCAD by creating a text entity representing the geologic letter symbol within the polygon. These text entities may be visible or not. GSMCAD text entities can include any number of built in leaders, and the far end of a leader is sufficient to create an attributed label point in the polygon where the leader terminates. While text points are being created, buttons labeled with various geologic symbols appear on the side of the screen so that the user can switch from labeling one unit to labeling another by clicking on the appropriate button.
Types of entities supported by GSMCAD include lines, splined lines, 3-D (profile) lines, polygonal shapes, linkable data points, rotational data points (strike and dip), unlinked symbol points, text points with (optional) leaders, and splined text.
Attribution of lines and points traced from original copy on a digitizing tablet is done using the keys on the digitizer keypad as the entities are created. Three standard numeric attributes of CODE, PARAMETER 1, and PARAMETER 2 are applied to all entities, but only need to be entered when there is a change from the previous entity. The speaker on the computer pronounces audible prompts for data entry and echoes the keys pressed for confirmation. This minimizes the need to look from the tablet to the screen. The <0> key starts an entity and sets additional points, and the <1> key ends the entity (creating or snapping to nodes for the first and last points of lines). The <4> and <5> keys have similar functions except that they snap to the nearest point before setting a coincident point, assuring a gap-less connection on lines even when points are set beyond the automatic snap distance. The <2> and <3> keys close polygons. The <8> key starts automatic collection of points that continues until some other key is pressed. The effect is similar to repeatedly pressing the <0> key or to holding the <0> key down while moving the puck, except that the program measures distance traveled and angle of inflection to minimize collection of unnecessary points. On curves, points may be as close as every 0.03 inches and on straight segments as distant as 0.3 inches. Use of the <8> key requires a steady hand but is the fastest way to enter line data. Entities partially digitized may be abandoned by pressing the <E> key. The screen window can be changed by digitizing new corners (<B> key) or a new center point (<C> key). Rotatable symbols can be entered either by keying in the rotation angle or by digitizing the observation point and a point on the end of the symbol so that the program can calculate the rotation.
Both mouse and digitizing tablet are active at the same time so that points digitized on screen can be combined with those from the tablet if convenient. Existing entities can be edited from the digitizing tablet.
The GSMCAD symbol set includes 155 of the most common symbols appearing on USGS geologic maps. Seventy of the symbols are rotating symbols that may have associated inclination angles posted nearby such as the bedding strike and dip symbol. Thirteen are symbols to be placed along a decorated line such as triangular teeth along a thrust fault. The remaining seventy two are miscellaneous symbols such as those representing quarries, drill holes, and mine shafts. Additional symbols can be defined by the user. The line decorations are automatically positioned at specified intervals along the appropriate line. Polygonal areas can be automatically filled with randomly oriented symbols or hatchures to produce a zipatone-like overprint. Posting points on the rotatable symbols are automatically positioned, but can be moved by hand to eliminate overposting. All symbols are carried as lines at the defined map scale on export to Arc/Info or DXF, eliminating the need for special symbol sets in Arc/Info, ArcView, AutoCad, or MapInfo. Observational symbols (in contrast to line decorations) are also carried as attributed points so that specialized Arc/Info symbol sets or AutoCad blocks can be used if desired.
GSMCAD fonts include many specialized geologic letter symbols as well as subscripts and superscripts in addition to the Cambrian, Triassic, and Pennsylvanian symbols. Unfortunately these letter symbols are not exportable. Various Arc/Info font sets include subsets of this collection, but I am unaware of any as comprehensive as the GSMCAD font set. The most common special symbols are translated from GSMCAD fonts to Arc/Info fonts in Arc/Info by the GSMDRAW.AML arc macro language program.
A complete set of CAD editing functions is available. Entities can be moved, dragged, copied deleted, or changed; singly, in groups, or globally. Entities can also be queried and lines broken (nodes added). Points within entities can be moved, added, or deleted. Nodes can be moved. All editing features can be accessed via pull-down menus and most can be invoked with a single keystroke. Use of hot key commands and mouse pointer is the fastest way to edit and accounts for much of the efficiency of GSMCAD. Attributes can also be changed by on-screen editing of data tables.
Correct topology for construction of polygons is partially achieved in GSMCAD by various operations on nodes. Nodes can be created by creating a line or by breaking a line. They can be selected and moved, carrying with them the ends of the associated lines. If one node is created or moved to a point within a defined snap distance of another, its position will be moved to coincide with the older node and it will merge with the older node and cease to exist separately. If the <nodes> option under the DISPLAY menu is toggled on, hanging nodes will be displayed as red squares and snapped nodes as black circles. Eliminating all hanging nodes on lines that should bound geologic units is the first step toward proper polygon topology.
The general utility of GSMCAD is based on its ability to produce Arc/Info coverages and CAD drawings in DXF format through its export functions. Both exports transfer all the special symbols, and the export to Arc/Info transfers the most common special letter symbols. The export to Arc/Info process is a combination of the GSMCAD export function and two arc macro language (AML) programs that run under Arc/Info. The process is relatively quick and transparent, so the user does not have to be trained in Arc/Info to produce necessary coverages and a graphics file of a geologic map in about 20 minutes.
The GSMCAD to Arc/Info export produces 18 ASCII files that must be transferred to an Arc/Info workspace. Those files are mostly paired ARC generate files of ground meter coordinates and attributes, but include three lookup files and a partial metadata summary. Entities are placed in those files according to their code description in the active GSMCAD plot file. For example, lines described as contacts are placed in the files used to generate the polygon coverage. The GSMARC.AML program converts the arc generate files into four coverages. The first is a geologic unit polygon coverage, the second includes all faults and other lines, the third includes points defining the location and attributes of symbols and arcs that draw out the symbols, and the fourth includes the visible text and leaders similar to an annotation layer. The GSMDRAW.AML program reads these coverages, lookup tables, and optionally a basemap grid to produce a graphics (.GRA) file of a colored geologic map on a base. The .GRA file can be printed using the Arc/Info RTL or POSTSCRIPT commands.
The DXF import command is less sophisticated than the DXF export, so only lines, polylines, and text are brought into GSMCAD. The primary function is to bring in lines vectorized from scans or collected from air photos on a digital photogrammetric plotter. Additional import/export features beyond those built into GSMCAD are provided by the GSMGIS DOS program (Selner and others, 1995) included with GSMCAD.
GSMCAD uses the standard Windows printer drivers to print parts of the map at any scale or all of the map fit to page size. It also produces HPGL2 output to drive a pen plotter or inkjet plotter. Colored geologic maps can be produced directly from GSMCAD if the polygons shapes have been built. It also has the unusual capability of plotting a properly registered drawing on a paper or film basemap mounted in a pen plotter by using the included HPGLUTIL utility.
A preliminary cross section diagram can be generated automatically from a profile line. A profile line is a special type of GSMCAD entity digitized with elevation values for each point. The points that should be digitized are where the line crosses known elevations such as topographic contours, ridge crests and valley bottoms, and geologic contacts and faults. The generated database will be in ground meter coordinates and includes a frame and labeled elevation tics. The ground profile is intersected by tics at geologic contacts and faults, and the tics project downward at the apparent dip calculated from the actual dip entered while digitizing the profile line.
GSMCAD is a Microsoft Windows program based on the GSMAP system of programs developed by Gary I. Selner and Richard Taylor starting about 1985. GSMAP was developed because commercial software specialized for the production of geologic maps on personal computers was not available. GSMAP was continually improved as personal computer capabilities increased and the 9th version was released in 1993 as U.S. Geological survey Open-File Report 93-511 (Selner and Taylor, 1993). In the absence of alternatives there was considerable interest despite slowness and difficulty of use. Many geologists in the USGS, state surveys, and government surveys around the world were trained and used the software in the late 80's and early 90's.
The advent of MS Windows offered opportunities to increase the speed and ease of use of computer programs, but GSMAP could not take advantage of these opportunities because it is a MSDOS-based program compiled from Quickbasic code. The answer was Visual basic, which allowed Quickbasic code to be ported to the Windows environment. The author began working with Gary Selner on the conversion in 1994 and began testing in 1995. The first official version was released in 1996 as GSMCAD (GSMAP CAD) to distinguish it from the DOS line that Gary Selner intended to continue. In the Windows environment many enhancements were possible, and revised versions of GSMCAD have been released on the Web frequently as new features are added.
The utility of GSMCAD is sometimes questioned as the Arc/Info GIS program becomes more firmly established as the preferred (even required) method of producing digital geologic maps at the USGS and in the wider world. However, the difficulty of learning Arc/Info and the expense of required equipment made rapid conversion to Arc/Info difficult, so GSMCAD was enhanced to produce ARC generate files, and AML (arc macro language) programs were written to run within Arc/Info and produce Arc/Info coverages and graphic image files of geologic maps from GSMCAD databases. This allowed geologists and temporary student employees to produce good digital data without the intimidating challenge and training expense of learning Arc/Info. Additional benefits were that the easy step of learning GSMCAD was good preparation for learning Arc/Info as the geologists' confidence increased, and that digitizing and editing in GSMCAD was faster than in Arc/Info. The GSMCAD to ARC conversion was based on a method developed by Greg Green and Gary Selner (Selner and others, 1995). The structure of the Arc/Info coverages produced by the AMLs was influenced by the ALACARTE AML program (Fitzgibbon and Wentworth, 1991).
The latest enhancements to GSMCAD have emphasized direct digital collection of points and lines in the field using GPS receivers, laptop computers, and digital orthophoto images.
The GSMCAD program is better optimized for the geologic data input needs of many USGS central region National Cooperative Geologic Mapping Team geologists than any available commercial program. The proliferation and sophistication of new commercial programs suggests that this may not be true in the future. Until that time the author intends to continue adding features to the program that facilitate his own mapping or that are requested by other users. The most likely features to be added next are background display of digital raster graphic topographic maps and linking with Apple Newton/Fieldlogger or palmtop data logger systems. Other possibilities include optimization for direct export to Adobe Illustrator/Avenza MapPublisher, export of Arc/Info shape files, and linking to Microsoft Access and dBase files.
Fitzgibbon, Todd, and Wentworth, Carl, 1991, ALACARTE User Interface -- AML Code and Demonstration Maps, Version 1.0: U. S. Geological Survey Open-File Report 91-587A.
Selner, Gary. I., Green, Gregory N., and Hoffman, J.D., 1995, GSMGIS: A program to import and/or export data between GSMAP data bases and various commercial and public domain products including Arc/Info, GRASS, IDRISI, EarthVision, GIV, Rockware STEREO, and MAPINFO: U. S. Geological Survey Open-File Report 95-570, 34 p., one 3.5-inch disk.
Selner, Gary. I., and Taylor, Richard B., 1993, System 9, GSMAP, and other programs for the IBM PC and compatible microcomputers, to assist workers in the earth sciences: U. S. Geological Survey Open-File Report 93-511, 363 p.
Williams, V.S., Selner, G.I., and Taylor R. B., 1996, GSMCAD, a new computer program that combines the functions of the GSMAP and GSMEDIT programs and is compatible with Microsoft Windows and Arc/Info: U.S. Geological Survey Open-File Report 96-007, 18 p., one 3.5-inch disk.