WinDisp Contour Menu

Contours

The Contour Specification menu controls how contours are to be displayed. When the Contour menu item is clicked for the first time the user is first prompted to select a contour file which is to be displayed. This file needs to have been generated previously and both UNIX and DOS formats are permissible. Once a contour file has been selected the default menu displayed is as follows:

Defining Contours

How the contour file is displayed is controlled by specifying up to 16 contour ranges. Each of these ranges is displayed in one row of the grid in the upper portion of the Contour Specification menu. The first 8 lines will normally be visible, with the remaining 8 lines accessible through use of the scroll bar on the right of the grid box. Each contour range is defined by a pen colour and five numbers :-

• Minimum
• Maximum
• Increment
• Density
• Label Size

When a contour level is checked to determine if it is to be plotted, each valid contour range is scanned starting with the first. Once a contour range which applies to the contour level is found, scanning is terminated and the definitions for that range applied to the display of the contour level. If no contour range is found for a particular contour level read from the file, the contour level will be discarded.

Minimum, Maximum

These two values specify the starting and ending values for a particular contour range. The minimum value must be less than or equal to the maximum value and the range covered includes both minimum and maximum values.

Increment

This value refines the selection of which contours between the specified minimum and maximum values are to be displayed. If a contour level is found which is greater than or equal to the minimum and less than or equal to the maximum, the contour level is then checked to determine if it is an integral multiple of the specified increment above the minimum value. Only those contours which are integral multiples of the increment will be displayed. Any contour range for which the contour increment is zero will not be used in plotting contours.

Density

Once a contour level which is greater than or equal to the minimum and less than or equal to the maximum and is an integral multiple of the specified increment above the minimum value, it will then be displayed using the density parameter to determine where to mask the contour line in areas of high gradients. This is necessary to avoid plotting too many contours in areas where the contour levels change rapidly. The density parameter is (approximately) measured in lines per cm, so a larger number will result in fewer contour lines being masked. The decision process as to which part of the line to mask is also based on the increment parameter. Any contour range for which the contour density is zero will not be used in plotting contours.

Label Size

This parameter specifies the size of label to display for contours plotted using the particular contour range. This value is specified in cm, and setting this value to zero results in no labels being plotted. The Automatic Labelling Increment and Default Line Label Size parameters (see description below) have precedence over the Label Size value.

Line Colour

The final item required to specify a contour range is the pen colour. When the user clicks on the grid in the pen colour column, the Pen Colour Specification Menu is displayed allowing the user to select and define pen colour to use to plot the lines in the current contour range. When a line is to be labelled using the specified Label Size, the label is displayed using the specified Line Colour.

In addition to the values specifying each of the contour ranges, there are a further four values which influence how contours are displayed, these are:

Contour Line Label Spacing

This value specifies the target separation between consecutive labels on an individual contour line and is measured in cm. If labels are to be displayed for a particular contour line, potential label positions are examined starting at 1 cm from the start of a displayed line segment and then at intervals of the Line Label Spacing from each label displayed. Labels will only displayed on line segments which are found to be relatively straight. If a label cannot be plotted on a segment because it is not straight enough, the labelling position is moved along the line in 1cm steps until either the end of the displayed line segment is reached or a suitable position is found.

Automatic Labelling Increment

This value provides a global value for selecting lines which are to be labelled. If the Automatic Labelling Increment is specified as a non-zero value and the Default Line Label Size is also greater than zero, then all contour lines which are an integral multiple of the Automatic Labelling Increment will be annotated with contour labels.

Default Line Label Size

This value specifies the size in cm of labels to be plotted for lines which are multiples of the Automatic Labelling Increment. If this value is zero, the Automatic Labelling Increment is ignored.

Contour Line Label Colour

This item permits the user to specify the colour to be used for displaying labels selected on the basis of the Automatic Labelling Increment. Any label plotted on the basis of the Automatic Labelling Increment will be displayed using the Contour Line Label Colour rather than the specified line colour which would otherwise have been applied to the label.

The final items available on this menu are :

Convert to Shape File

Clicking on this command button will result in the contour file being processed according to the current contour definitions and map scale and exported as a shape file which can then be imported into ArcView. Note that the map scale should be set to be the same as the target scale to be used for displaying the contours in ArcView so that the density masking is applied correctly.

Change Contour File

Clicking on this button brings up a dialogue box which allows the user to select another contour file. The current contour definitions will otherwise remain unchanged. Note that the Change Contour File dialogue can also be invoked by double clicking on the Contour File text box.

Cancel

Clicking on this box will cancel any changes made since entering the Contour Definitions menu.

OK

When this button is clicked, the current Contour definitions are checked for validity and the user notified of any problems are found. If no problems are located, the Contour Definition menu will be closed and control will return to the main WinDisp window.

Options Menu

There are two options available from this menu:

Save Contour List

Clicking on this menu item will present the user with a file save dialogue from which the user may select the name and location of a file in which to store the current contour definitions. All the current contour definitions (including the Automatic Labelling parameters) are save to the file. This file is a simple text file and can be edited by the user.

Read Contour List

Clicking on this menu item will present the user with a file read dialogue from which the user may select the name and location of a file from which to read contour definitions. The contour definitions will be read from the file and will replace the current definitions.

Manipulating the Contour Range Grid

The Contour Range grid responds to a number of keys to assist the user in specifying contour ranges. When the user clicks on a text item on the grid, an edit text box is located at that position to enable the value to be changed. When the edit text box is displayed, the normal editing keys become operational and copying and pasting is also available.

If the user clicks on the first column containing the number of the contour range, the number will have an asterisk appended indicating that the range will not be used for displaying contours. This feature is provided as a simple means for turning off labelled contour levels when changing to a larger map scale without forcing the user to completely redefine the contour definitions. To turn the contour range back on again, simply click again on the first column in the row.

If the user clicks on the first column in a row and then presses the delete key, that contour range will be deleted from the grid and all subsequent ranges will be moved up by one row. The values deleted from the row are saved and if the user clicks on the first column in another row (or the same row) and presses the insert key, the current and subsequent rows will be moved down the list and the saved row inserted at the current position. Note that if all 16 ranges are in use, the last contour range will be lost.

The following menu displays the contour definitions used in generating the sample contour plot.

In this menu the contour range 2 will not be displayed, all contours which are multiples of 50 between 50000 and 54000 will be plotted using a black pen and will be labelled using text 0.25cm high.

Send mail to john.paine@onaustralia.com.au with questions or comments about this web site.
Last modified: April 10, 2012