The selections in the Plot pulldown menu allow the modification of plot parameters. There are popups for setting the scaling of the axes, the number of tick marks to display, legends, writing annotative text, and drawing objects such as lines and boxes.
xmgr uses 3 coordinate systems in drawing a graph. These are the world, viewport, and device coordinate systems (following Foley and Van Dam). The world coordinates system is the one in which the data are defined and constitutes the user's coordinate system. The viewport coordinate system (in xmgr), is a rectangle defined by the points (0.0, 0.0) or the lower left corner of the device and (1.0, 1.0) or the upper right corner of the device. The pipeline for drawing objects on the screen or hardcopy device is a pair of linear transformations that carry points in world coordinates to the viewport and then on to the device coordinate system. The upshot is that an object located in world coordinates can be drawn in various parts of the screen or hardcopy device depending on the scaling while an object located in viewport coordinates remains in the same spot regardless of the world scaling. Strings, lines, boxes, and the graph legend can be located in either world or viewport coordinates.
Define the world coordinate system by filling in the items Xmin, Xmax, Ymin, and Ymax. The plot is drawn in world coordinates in a rectangle described by the two points (Xmin, Ymin), (Xmax, Ymax). The input is scanned for arithmetic expressions so setting Xmin = -PI and Xmax = PI is legal input (see the section on transformations for a description of the syntax and available functions). The tick spacing can also be set in this popup by filling in the items for the major and minor spacing for each axis. `Update world/ticks' is used, when, occasionally, the state of the items used to define the world scaling get out of sync with what is actually used to draw the graph, clicking on this item synchronizes the internal values with the displayed values. Press the button marked Accept to inform xmgr of the changes.
Note: make sure Xmin < Xmax and Ymin < Ymax.
Define the viewport by filling in the items Xmin, Xmax, Ymin, Ymax. Viewport coordinates run from (0.0,0.0), the lower left corner of the screen or hardcopy device, to (1.0,1.0), the upper right corner of the screen or hardcopy device. Press the button marked Accept to make the change to the new viewport. Press the Pick view button to use the mouse to define the viewport. Take the mouse to the lower left corner of the desired viewport and press the left button (there is no need to hold the button down). A rubberband box will show you the current size of the viewport you may select. When you are satisfied with the view, press the left mouse button again to activate the new viewport.
Press the button marked Close to close the Viewport popup.
The viewport can also be changed by double clicking on the focus markers (or where they would be placed if not shown). The new location is chosen by clicking the first mouse button.
Use the Autoscale popup to set parameters associated with autoscaling. Select the axis to scale, or none. Selecting none allows the autoscale type and the number of ticks to create to be set but no autoscaling is done. Select the particular set to use or All. The Autoscale type sets the method of autoscaling, either Auto or fixed. Auto uses a method based on routines posted to the net by Paul Heckbert and generates nice looking tick spacing, but alters the scaling of the axes. The fixed option uses the minimum and maximum values in the set (or over all sets) to set the scale of the axes. Select the number of tick marks to use for defining the tickmark spacing (in the case of Heckbert scaling, these settings are advisory only). The item labeled Apply to: allows the autoscaling of the current graph, or all active graphs.
The title and subtitle are strings that appear centered at the top of the plot. Fill in the items indicated and press the button marked Accept. To change the font, color, or character size used for titles use the items from the popup denoted Props....
Set the spacing and type of major and minor tick marks, definition of axes labels, and toggle features associated with the drawing of the graph axes.
The top item, Edit, selects the axis for which the feature selections will apply. There are two axes defined for each co-ordinate direction, the primary axis and the zero axis. The primary axis will be used the most, the zero axis is, by default, turned off. The button to the right of the Edit item labeled Props... allows the axis to be offset by a specified amount in viewport co-ordinates. The item Axis label accepts the definition of the label to be used when drawing the axis. Various properties of the label may be set in the popup just below labeled Axis label props....
The two items `Major tick spacing' and `Minor tick spacing' set the spacing of major and minor ticks. Tick labels are drawn based on the setting for the major tick spacing. These items are duplicated in the `Define world' popup described previously. Fill in the appropriate blanks and press Accept to refresh the display. The units are positive deltas starting with the world minimums. Input is run through the scanner so expressions are allowed. The are special symbols dx and dy for setting a prescribed number of tick marks. Dx is the distance along the X-axis and dy is the distance along the Y-axis, as defined in the current window of the world coordinate system. Typing at Major tick spacing "dx/10" will give 10 major tickmarks.
Tick labels, tick marks, the axis bar, may be toggled by the check boxes. Properties for each of these can be set by the Props... popups associated with each item.
Properties for tick labels are:
Press the button Accept when everything is OK, or Close to close the popup.
Properties for tick marks are:
Press the button Accept when everything is OK, or Cancel to close the popup.
Properties for the axis bar are:
Color, line width, and line style items set the characteristics of the lines use to draw ticks and grid lines.
Press the button `Accept' when everything is OK, or `Cancel' to close the popup.
IMPORTANT NOTE FOR LOG PLOTS: When log scaling is selected for a particular axis or axes, the meaning of major and minor ticks changes slightly. Major ticks should be set to integer values. Use minor ticks to set the number of interdecade tickmarks, these should be set to integer values ranging from 0 (no interdecade tickmarks) to 5. A value of 1 will draw each interdecade position, 2 will skip every other position, etc.
The frame is the box drawn around the clipping region of the graph, and the region inside. Items in the frame popup are:
The items in the symbols popup allow the selection of symbols, lines, and fill style to be used when drawing a set.
Items in the symbols popup are:
NOTE: There are limits on how large a set can be for the fill to operate correctly. The limit for the display is approximately 8000 points, for the hardcopy drivers, this limit drops to around 800-1000.
NOTE: symbols 16-29 do not appear in the legends
Error bars are created by reading in the data as a set with error bars (see Files above). Properties of error bars are set by opening the `Error bar props' popup.
Clicking Place is a convenient method of placing the legend on the canvas. After pressing this button, move the mouse pointer to the desired location and press again with the left button. The location will be in world or viewport coordinates as selected above.
Press the button marked Close to close the popup.
The numbers of strings, lines, boxes and ellipses are fixed, open Help/About to see what the limits are for your version of xmgr.
To click on a text string, the cursor must be placed near the origin of the text string. The origin will be the lower left corner of the string for left justified strings, the right side for right justified strings and in the center for center justification.
NOTE: It is necessary to press <return> to register the string.
^e - Move editing cursor to end of string
^u - Delete beginning of string to cursor
^k - Delete to end of string
The cycle "Position in: World | viewport coordinates" allows the object position to be defined in the world coordinate system or viewport coordinates. In World coordinates, the object position and aspect ratio on the display change as the plot is re-scaled. Specifying the object in viewport coordinates will force the object to remain in the same place and retain the same aspect ratio as the plot scale is changed.
When the cursor turns to cross-hairs, the two points defining the object may be specified. A line is defined by its end points while a box is defined by its opposing corners. An ellipse is defined by the opposing corners of the rectangle enclosing it.
Press the button marked "Move", this should change the cursor to the "move" cursor.
Select the object to be moved. The object will now be drawn with the first point used to define the object under the cursor.
Move the cursor to the new location and press the left mouse button.
Select the object to be deleted.
The attributes of an object may be changed after it has been defined by clicking on the object. Editing may be used to redefine a line, box, ellipse or string.
The World<->View button is used to interchange between world and viewport specification of object placement. The object will remain at the same spot when converted from one coordinate system to the other.
Set the display of a string containing the current time. This string is updated each time the graph is redrawn.