The link between ArcView 3.0b and XGobi is designed to combine the strengths of both packages in the exploration and analysis of data collected in a spatial framework. ArcView 3.0b is a geographic information system (GIS) that allows spatial data in many forms to be displayed, queried, and manipulated. XGobi is a dynamic graphics program that allows multivariate data to be explored through the manipulation of scatter plots. XGobi provides tools for the exploration of multivariate data such as linked brushing, identification, the grand tour, and projection pursuit.
The link allows data collected at spatial locations (stored in ArcView) to be dynamically passed to XGobi and explored. The link between the data points in XGobi and the locations from which they were collected is maintained through "linked brushing". Linked brushing, as used in this context, is the ability to change the glyph/size/color of the points in either ArcView or XGobi and to see the corresponding points in the other application change simultaneously.
The link comes in five flavors. One flavor, that we call Vanilla (or the multivariate link) simply passes the data associated with each spatial location into XGobi and allows it to be analyzed. The second flavor, Chunky Monkey (or the CDF link) takes data from an attribute and calculates and displays its empirical spatial cumulative distribution function (CDF). This version of the link allows multiple regions to be specified for CDF prediction and display. The third flavor, Strawberry Sundae (or the variogram-cloud link) calculates and displays variogram-cloud plots that can be interactively explored. This version of the link is used when exploring a data set for spatial dependence. The fourth flavor, Cherry Garcia (or the lagged scatterplot link) creates and displays dynamic lagged scatterplots. The fifth flavor, Wavy Gravy (or the multivariate variogram-cloud link) calculates and displays a special type of variogram-cloud that is used to look for asymmetric, multivariate spatial dependence. Linked brushing is available in all versions.
This linking makes the combination of ArcView and XGobi a powerful tool for the exploration of spatially referenced data.
To use the link it must first be extracted from a UNIX® tape archive
(tar) file and two UNIX environment variables must be set. The
programs are currently compiled for DEC Alpha workstations, which was
also our development platform. After recompilation, the programs can also
be used on Sun/Sparc and SGI workstations (and perhaps others we have not
tested yet). Due to a different implementation of the RPC mechanism
for (regular) DEC workstations, it is not possible to use the
link on these platforms.
To use the link, you must have ArcView 3.0b on a Unix (X-windows) workstation. On slower machines, with less memory, the linking between applications can become slow. For more complex types of linking, the faster the machine the better. The new version of the link requires that Dialog Designer is installed. The dialog designer extension can be downloaded for free from the ESRI web site.
If you were using the older version of the link ( ArcView 2.0 - XGobi Link Version 1.3), you will need to remove the default.apr file from your home directory. The new version is distributed as an extension and is accessed through the Extension dialog box in ArcView3+.
tar File The program is distributed as a compressed UNIX tar
file. Click on this link to download the file
av2xgobi.tar.gz
or you can download the ArcView scripts only if you already have the current version of XGobi installed by clicking on this link avxglinksrc.tar.gz . Store this file in
a new directory, say axx1.5, and cd into this
directory. To
install the ArcView/XGobi link, uncompress this file and extract the
individual files from the archive with the commands:
gunzip av2xgobi.tar.gz tar -xvf av2xgobi.tar
This will create two subdirectories (under the current working directory) named av_dir, and xgobi.
Once the files have been extracted from the archive, two environment variable containing the locations of the ArcView and XGobi code must be set. For example, in tsh you can do this by:
setenv AV2XGOBI_HOME directory1 setenv XGOBIDIR directory2e.g., on our system these would be
setenv AV2XGOBI_HOME /home/arcview-xgobi/axx1.5/av_dir setenv XGOBIDIR /home/arcview-xgobi/axx1.5/xgobiThese lines are typically added to the
.cshrcfile (or, on Project Vincent at ISU, the.cshrc.minefile).Actually, there are two additional environment variables that the link accesses, but most systems set these automatically. They are:
If your machine does not automatically set these variables, you will have to do it manually.
The easiest way to access the AV2XGobi.avx extension from within ArcView is to set another environment variable that tells ArcView where to look for user extensions:
setenv USEREXT path_to_directory
e.g., on our system this would be
setenv USEREXT /home/arcview-xgobi/axx1.5/av_dir
Alternatively, you can copy the file named AV2XGobi.avx from $AV2XGOBI_HOME/av_dir into either your home directory (this must be done for EACH user who wants to use the link) or into $AVHOME/ext/ (where $AVHOME is the directory where arcview lives). The link is then available to all users. ArcView checks your home directory and the $AVHOME/ext/ directory for extensions in that order.
To use one of these sample Makefiles you have to cd into the XGobi src directory, rename the Makefile, and then compile XGobi:
cd $XGOBIDIR/src mv Makefile.xgobi.<platform> Makefile make
To compile on a different platform, or if the above does not work you have to create a new Makefile.
cd $XGOBIDIR/src rm MakefileWhen running the link to ArcView (and optionally to XploRe) you need to compile XGobi with RPC mechanism enabled. You will need to uncomment one of the following lines in the file Imakefile:
# If using RPC ... EXTRA_DEFINES = -DRPC_USED # ... also, uncomment this #define
to use just the RPC mechanism OR
# If using to communicate with XploRe ... EXTRA_DEFINES = -DRPC_USED -DXPLORE
to use XploRe with ArcView and XGobi.
Then you have to make the Makefile and compile XGobi:
xmkmf makeYou should now get an xgobi executable. If you have problems compiling XGobi please take a look at the XGobi Web page first and contact us if you still cannot solve the problem. Finally you have to copy the xgobi exectuable into the bin directory:
cp xgobi ../bin/.
On some systems, XGobi needs to be compiled with a regular C compiler, but in general the GNU C compiler can be used. Depending on your UNIX environment, you may have to modify the makefiles, e.g., to add/modify paths directing to the required X libraries or to include libraries required for the RPC mechanism. If you are able to compile the programs for platforms other than those specified, we would appreciate a copy of your makefiles.
If you are used to the older version of the link (ArcView 2.0 - XGobi Link Version 1.3), be aware that there is no equivalent to AV2XGobi in this current version. You do not have to worry about getting parts of the XGobi source files from a different location. Now all XGobi source files that are required to support the ArcView (and XploRe) link are distributed as a part of the original XGobi distribution.
If you have projects that were created using old versions of the link you can update them to be compatible with the new version of the link, and arcview3. To update a project first before opening the project delete the default.apr file from the old version of the link from your home directory. Open the project you wish to update and make sure you unload any extensions from the project. From the Project menu choose Customize, the following window should appear,
Choose the reset button with the mouse, and the project should revert to orignal settings. Now you should be able to add the AV2XGobi extension without conflicts.
In the new version of the ArcView/XGobi link we have moved from distributing the link as a default project to an ArcView Extension that can be added and removed by the user at will. We have made some changes to the GUI, e.g., adding a new button to toggle the backgound on and off.
Toggling between the five flavors of the link has been improved. In the old version we had a seperate GUI for each link that needed to be loaded each time the link was changed. Now the appropriate buttons are added and removed directly from the view GUI by the toggle script. Cloning XGobi, to get several views of the data, is now done directly in XGobi, rather than through the ArcView GUI.
Finally the link now supports missing values for four of the flavors (excluding the SCDF link).
Each of the links has a separate graphic user interface (GUI).
To use a link, load the GUI for that link and start it up. The link
GUIs are loaded using the XGobi pulldown menu in the View
Document GUI.
The XGobi pulldown menu has 6 options:
After the appropriate GUI has been loaded, you can start up the link following the instructions given below.
The Vanilla flavor of the link allows (multivariate) data
associated with a point theme in ArcView to be passed into XGobi and
be explored. The GUI for this version of the link contains several
additions to the View document GUI (Figure 2). The Menu Bar
contains additional pulldown menus that allow the glyph/size/color to
be set. The Button Bar contains three additional buttons: 1) a
green diamond that initiates the link; 2) a red diamond that
terminates the link; and 3) a copy object icon that clones the XGobi
window. The Tool Bar contains an additional brush tool that
allows points to be brushed in ArcView.
Initiating the LinkThe green diamond button on the Button Bar is pressed to initiate the link. Before the link can be initiated a point theme must be made the only active theme. A label point theme can also be used to analyze polygon data. Active theme entries in the View Table-of-Contents have a raised appearance. When the link is initiated, all of the visible, numeric fields in the "Attributes of <theme>" table are passed into XGobi and the XGobi window is initiated. You can control how much data is passed into XGobi by setting the visible fields in the Table Properties dialogue.
When initiated, the user will be prompted to specify a field that will be used as row labels in XGobi. This is the field that will be used in the XGobi Identify panel, and typically is some sort of an identifier.
Depending on the speed of your computer, the size of the point theme, and the number of fields being analyzed, this might take one to two minutes to complete. Be patient.
Once initiated, any glyph/size/color brushing conducted in the XGobi window will be automatically passed to ArcView, which brushes corresponding points. Both transient and persistent brushing are allowed. Points can also be erased using XGobi erase brushing.
NOTE: Avoid using the XGobi Reset pulldown in the Brush menu to reset either glyphs or colors. This isn't communicated back to ArcView.
Brushing in ArcViewBrushing in ArcView is done using the Brush Tool on the Tool Bar (Figure 2). When this is the active tool, the user can define a polygon on the View Display. Any points within the user defined polygon are persistently brushed in the current glyph/size/color and this brushing information is passed to XGobi, which brushes corresponding points. The current glyph/size/color are set using the Glyph/Size/Color pull down menus.
Toggle the BackgroundThe View background is automatically set to the same color as the XGobi background. This background can be toggled on and off using the toggle button on the Button Bar).
Terminating the Link The Chunky Monkey flavor of the link allows regional
univariate or bivariate empirical CDFs to be displayed and
explored. The GUI for this version of the link contains several
additions to the View document GUI (Figure 3). The Button Bar
contains three additional buttons: 1) a green diamond that initiates
the link; 2) a red diamond that terminates the link; and 3) a "U" icon
that updates the CDF plots after region definitions have been
changed. The Tool Bar contains two additional tools: 1) a
region definition tool that allows regions to be defined for which
CDFs will be calculated; and 2) a brush tool that allows transient
brushing in ArcView.
Initiating the LinkThe green diamond button on the Button Bar is pressed to initiate the link. Before the link can be initiated a point theme must be made the only active theme. A label point theme can also be used to analyze polygon data. When the link is initiated, the user is prompted to choose either univariate or bivariate CDFs and then to enter the appropriate number of fields from the "Attributes of <theme>" table for which CDFs will be calculated. The data from this field are passed into XGobi where the empirical CDF is calculated and displayed. Initially, the CDF is calculated for the entire region defined by the active point theme.
Defining Regions for
CDF CalculationAfter initiating the link, spatial regions can be interactively defined for which CDFs will be displayed. When the Define Regions tool is active, user defined polygons can be entered on the View Display. As each polygon is entered, it is given a color (automatically) and the CDF for the defined region is displayed in the XGobi window using the same color. Currently, up to 10 regions can be defined. Region polygons can be deleted or modified (see Updating Regions below) using ArcView's object manipulation tools.
Updating RegionsSpatial regions can be modified using ArcView's object manipulation tools. After a region has been modified, however, the Update Region button must be pressed in order for the change to be reflected in the CDF view.
Once the link is initiated, the CDFs in the XGobi window can be brushed with different glyphs. No color brushing is allowed (because colors are used to identify regions) and only transient brushing is allowed. When brushed, the corresponding points in ArcView are brushed using the specified glyph.
Brushing in ArcViewLocations in ArcView can be brushed to see where they are in the CDF plots. This is done by using the Brush Tool to define a polygon. The points in the CDF plots are given a larger glyph. The points in ArcView are not changed.
Toggle the BackgroundThe View background is automatically set to the same color as the XGobi background. This background can be toggled on and off using the toggle button on the Button Bar).
Terminating the LinkThe Strawberry Sundae flavor of the link allows variogram-cloud plots to be displayed and be explored. The variogram-cloud link is used when exploring the spatial dependence in a data set and when looking for spatial outliers. In this option, the points displayed in XGobi represent all possible pairs of sampling locations. For each pair of locations, XGobi plots the square-root of the absolute difference between attribute values at the locations versus the euclidean distance between the locations. In data sets exhibiting strong spatial dependence, the variance in the attribute differences will increase with increasing distance between locations. Locations that are near to one another, but with large attribute differences, might indicate a spatial outlier, even though the values at both locations may appear to be reasonable when examining the data set non-spatially.
Because each point in the XGobi window corresponds to a pair of sampling locations, the brushing environment is altered slightly. For each point that is brushed in XGobi, a line is drawn between the corresponding pair of sampling locations in ArcView. Because each sampling location can be included in up to n points being displayed in XGobi, brushing a location in ArcView causes two things to occur: 1) all corresponding points in XGobi are brushed; and 2) lines are drawn in ArcView between the brushed location and all other locations with which it is paired.
When initiated, this link calculates and passes p^2+5 variables into XGobi, where p is the number of visible, numeric fields in the attribute table of the active point theme. The visible fields can be changed in the Table Properties dialogue. The following variables are calculated:
is the value of attribute
i at location s. There are p^2 of
these variables.
There are several notes and cautions about these variables:
The GUI for this version of the link contains several additions to
the View document GUI (Figure 4). The Menu
Bar contains additional pulldown menus that allow the
glyph/size/color to be set. The Button Bar contains three
additional buttons: 1) a green diamond that initiates the link; 2) a
red diamond that terminates the link; and 3) a copy object icon that
clones the XGobi window. The Tool Bar contains an additional
brush tool that allows points to be brushed in ArcView.
Initiating the LinkThe green diamond button on the Button Bar is pressed to initiate the link. Before the link can be initiated a point theme must be made the only active theme. A label point theme can also be used to analyze polygon data. Active theme entries in the View Table-of-Contents have a raised appearance. When the link is initiated, the user will be prompted for the maximum distance between pairs of points. Only pairs of points that are less than or equal to this distance apart from one another will be passed into XGobi. This allows the amount of the data being passed into XGobi to be reduced dramatically if the scale of spatial dependence is dramatically smaller than the area being analyzed. This can help both the speed of beginning the link as well as the interpretation of the grahics.
Depending on the speed of your computer, size of the point theme, and the number of fields being analyzed, this might take one to two minutes to complete. Be patient.
Once initiated, any glyph/size/color brushing conducted in the XGobi window will be automatically passed to ArcView. For each point that is brushed in XGobi, a line is drawn between the corresponding pair of sampling locations in ArcView. The color of the line corresponds to the current XGobi brush color.
NOTE: Avoid using the XGobi Reset pulldown in the Brush menu to reset either glyphs or colors. This isn't communicated back to ArcView.
Brushing in ArcViewBrushing in ArcView is done using the Brush Tool on the Tool Bar (Figure 4). When this is the active tool, the user can define a polygon on the View Display. Because each sampling location can be included in up to n points being displayed in XGobi, brushing a location in ArcView causes two things to occur: 1) all corresponding points in XGobi are brushed with the current color/glyph/size (set in pulldown menus); and 2) lines are drawn in the ArcView window between the brushed location and all other locations with which it is paired.
In order to remove the lines that have been displayed in the ArcView window as a result of brushing, simply brush all affected points using the default color, i.e., the color that was used when the link was started. The sampling locations in the ArcView window will always remain this color; only the lines between locations will be given colors corresponding to the brush color. This unbrushing can be done in either the ArcView or the XGobi window.
Toggle the BackgroundThe View background is automatically set to the same color as the XGobi background. This background can be toggled on and off using the toggle button on the Button Bar).
Terminating the LinkThe Cherry Garcia flavor of the link allows dynamic, spatially lagged scatterplots to be displayed and be explored. Lagged scatterplots are a useful tool for initial exploration of spatial dependence in a data set. In this option the points displayed in XGobi represent all possible pairs of sampling locations. For each pair of locations, XGobi plots the following points:
where 
represents variable
l at location si, and 
represents variable m at location
sj.
If a data set exhibits strong spatial dependence, then the points in the plot that originate at sampling locations near to one another will be close to the line y=x and the dispersion about this line will increase as the distance between sampling location increases.
This variation can be explored by displaying the distance variable (d, see below) in a separate (cloned) XGobi window (see Cloning the XGobi Window below) and dynamically brushing through the distance point cloud. This provides a dynamic lagged scatterplot.
When initiated, this link starts XGobi with 2p+4 variables, where p is the number of visible, numeric fields in the attribute table of the active point theme. The visible fields can be changed in the Table Properties dialogue. The following variables are calculated:
in the formula for the
lagged scatter plot. When plotted against var_j, a lagged
scatterplot is formed. There are p of these variables.
in the formula for the
lagged scatter plot. When plotted against var_i, a lagged
scatterplot is formed. There are p of these variables.
There are several notes and cautions about these variables:
The GUI for this version of the link contains several additions to
the View document GUI (Figure 5). The Menu
Bar contains additional pulldown menus that allow the
glyph/size/color to be set. The Button Bar contains three
additional buttons: 1) a green diamond that initiates the link; 2) a
red diamond that terminates the link; and 3) a copy object icon that
clones the XGobi window. The Tool Bar contains an additional
brush tool that allows points to be brushed in ArcView.
Initiating the LinkThe green diamond button on the Button Bar is pressed to initiate the link. Before the link can be initiated a point theme must be made the only active theme. (A label point theme can also be used to analyze polygon data.) Active theme entries in the View Table-of-Contents have a raised appearance. When the link is initiated, the user will be prompted for the maximum distance between pairs of points. Only pairs of points that are less than or equal to this distance apart from one another will be passed into XGobi. This allows the amount of the data being passed into XGobi to be reduced dramatically if the scale of spatial dependence is dramatically smaller than the area being analyzed.
Depending on the speed of your computer, size of the point theme, and the number of fields being analyzed, this might take one to two minutes to complete. Be patient.
Once initiated, any glyph/size/color brushing conducted in the XGobi window will be automatically passed to ArcView. For each point that is brushed in XGobi, a line is drawn between the corresponding pair of sampling locations in ArcView. The color of the line corresponds to the current XGobi brush color.
NOTE: Avoid using the XGobi Reset pulldown in the Brush menu to reset either glyphs or colors. This isn't communicated back to ArcView.
Brushing in ArcViewBrushing in ArcView is done using the Brush Tool on the Tool Bar (Figure 5). When this is the active tool, the user can define a polygon on the View Display. Because each sampling location can be included in up to n points being displayed in XGobi, brushing a location in ArcView causes two things to occur: 1) all corresponding points in XGobi are brushed with the current color/glyph/size (set in pulldown menus); and 2) lines are drawn in the ArcView window between the brushed location and all other locations with which it is paired.
In order to remove the lines that have been displayed in the ArcView window as a result of brushing, simply brush all affected points using the default color, i.e. the color that was used when the link was started. The sampling locations in the ArcView window will always remain this color; only the lines between locations will be given colors corresponding to the brush color. This unbrushing can be done in either the ArcView or the XGobi window.
Toggle the BackgroundThe View background is automatically set to the same color as the XGobi background. This background can be toggled on and off using the toggle button on the Button Bar).
Terminating the LinkThe Wavy Gravy flavor of the link is designed to allow exploration of asymmetric, multivariate spatial dependence. A complete description is beyond the scope of this document. See Majure and Cressie (1996) for a more complete description.
The multivariate variogram-cloud link is very similar to the variogram-cloud link. The difference is that, because we are emphasizing the exploration of asymmetric, multivariate spatial dependence, the two variables g_ij and g_ji (from the variogram-cloud link) are combined into one variable, g_ij in this link. The new variable, g_ij, when plotted against the distance, d, is equivalent to plotting g_ij and g_ji end-to-end, that is, the horizontal axis for the plot g_ij extends to the right and the horizontal axis for the plot g_ji extends to the left. The resulting plot allows the analyst to observe the full multivariate spatial structure in one plot. If the structure in the plot is not symmetric about the origin, which is often the case in multivariate spatial data, this can be detected.
Note that when exploring multivariate data using the variogram-cloud link, the lagged-scatterplot link, or the multivariate variogram-cloud link, it is important to standardize the data (e.g., subtract the mean and divide by the standard deviation) to avoid spurious dependencies appearing that might be due simply to location and scale features.
Because each point in the XGobi window corresponds to a pair of sampling locations, the brushing environment is altered slightly. For each point that is brushed in XGobi, a line is drawn between the corresponding pair of sampling locations in ArcView. Because each sampling location can be included in up to n points being displayed in XGobi, brushing a location in ArcView causes two things to occur: 1) all corresponding points in XGobi are brushed; and 2) lines are drawn in ArcView between the brushed location and all other locations with which it is paired.
When initiated, this link calculates and passes (p choose 2)+5 variables into XGobi, where p is the number of visible, numeric fields in the attribute table of the active point theme. The visible fields can be changed in the Table Properties dialogue. The following variables are calculated:
is the value of attribute
i at location s. There are p choose 2 of
these variables.
There are several notes and cautions about these variables:
The GUI for this version of the link contains several additions to
the View document GUI (Figure 6). The Menu
Bar contains additional pulldown menus that allow the
glyph/size/color to be set. The Button Bar contains three
additional buttons: 1) a green diamond that initiates the link; 2) a
red diamond that terminates the link; and 3) a copy object icon that
clones the XGobi window. The Tool Bar contains an additional
brush tool that allows points to be brushed in ArcView.
Initiating the LinkThe green diamond button on the Button Bar is pressed to initiate the link. Before the link can be initiated a point theme must be made the only active theme. (A label point theme can also be used to analyze polygon data.) Active theme entries in the View Table-of-Contents have a raised appearance. When the link is initiated, the user will be prompted for the maximum distance between pairs of points. Only pairs of points that are less than or equal to this distance apart from one another will be passed into XGobi. This allows the amount of the data being passed into XGobi to be reduced dramatically if the scale of spatial dependence is dramatically smaller than the area being analyzed.
Depending on the speed of your computer, size of the point theme, and the number of fields being analyzed, this might take ont to two minutes to complete. Be patient.
Once initiated, any glyph/size/color brushing conducted in the XGobi window will be automatically passed to ArcView. For each point that is brushed in XGobi, a line is drawn between the corresponding pair of sampling locations in ArcView. The color of the line corresponds to the current XGobi brush color.
NOTE: Avoid using the XGobi Reset pulldown in the Brush menu to reset either glyphs or colors. This isn't communicated back to ArcView.
Brushing in ArcViewBrushing in ArcView is done using the Brush Tool on the Tool Bar (Figure 6). When this is the active tool, the user can define a polygon on the View Display. Because each sampling location can be included in up to n points being displayed in XGobi, brushing a location in ArcView causes two things to occur: 1) all corresponding points in XGobi are brushed with the current color/glyph/size (set in pulldown menus); and 2) lines are drawn in the ArcView window between the brushed location and all other locations with which it is paired.
In order to remove the lines that have been displayed in the ArcView window as a result of brushing, simply brush all affected points using the default color, i.e. the color that was used when the link was started. The sampling locations in the ArcView window will always remain this color; only the lines between locations will be given colors corresponding to the brush color. This unbrushing can be done in either the ArcView or the XGobi window.
Toggle the BackgroundThe View background is automatically set to the same color as the XGobi background. This background can be toggled on and off using the toggle button on the Button Bar).
Terminating the LinkProblem: ArcView is a color hog. When initiated, it seems to monopolize the entire machine colormap. When the link is initiated and XGobi comes up, it can't get the colors it needs.
Solution: Open a copy of XGobi before ArcView is started. XGobi then gets the colors it needs before ArcView has a chance to get them all. This doesn't seem to hurt ArcView.