WinDisp Marker Posting Menu

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WinDisp Marker Posting Menu

Marker Posting

This option produces a simple marker at each data point, the size or colour of which can be related to the selected data value. The menu for defining Marker Posting is :

This menu display contains a number of standard items which are displayed for all menu styles and a number of items which are specific to the particular posting style.

General Posting Options

Marker Specific Specifications

With marker posting only one data value can be selected. This data value is chosen from the available data items by clicking in the grid cell under the column heading Name of Data Variable. This brings up a drop down box from which the desired data variable can be chosen. Once the coordinates and data variable are defined, the user can check the range of data values contained in the file by clicking on the Display Data Range button. Clicking on this button brings up the Data Range Menu.

Use Colour Legends

The main item remaining on this menu which affect the Marker posting style is the Use Colour Legends check box. If this box is checked the colour of the posted data marker is determined by looking up the data value using the ranges specified in the colour legend. The legend ranges are scanned sequentially and if a range is found which spans the particular data value, then the corresponding pen colour is used to display the data marker. If no data range is found, the data marker will not be displayed.

Define Data Variable

After (optionally) determining the data range and area limits, the next step for displaying marker posting is to define the marker specific options by clicking on the Define Data Variable button. This brings up the following form:

Data Variable

This displays the user name of the currently selected data variable.

Minimum Value

This value specifies the minimum value for which the data marker will be displayed. If the data value is less than the minimum only the sample marker (if one is defined) will be displayed at the data location. If this value is set to be equal to or larger than the maximum value, the minimum limit is ignored.

Maximum Value

This value specifies the largest value which is to be used for displaying the data marker. If the data value is larger than the maximum value it is simply truncated to the maximum value. If this value is set to be equal to or smaller than the minimum value, the maximum limit is ignored.

Scale

This value represents the scale used to convert the data value into data marker size. The value is interpreted as units/mm and so must be a positive value. The data marker size plotted is computed using the formula:

size = min ( ( value - minimum ) , maximum ) / scale

Note that the minimum, maximum and scale values are ignored if the Use Colour Range check box is selected on the Post Specifications menu and the marker size is set to be the same as the sample marker label size. Which in this case will only be plotted if the data value is null or is outside the ranges defined in the colour legend.

Null Value

This text box displays the null data value for the current data variable, this value is provided for information only and the null data value should be changed on the Specify Data Names menu

Logarithmic Scaling

This check box specifies if the log (base 10) of the data value should be used in posting the data. If log scaling is selected, the minimum and maximum values are still interpreted in the original data units, but the Scale value is interpreted in log10 units. When posting log scaled data the radius of the marker used is computed using the formula:

size = log10( min ( ( value / minimum ) , maximum ) / scale

if both minimum and maximum are positive, and as

size = log10( min ( value , maximum ) / scale

if the maximum is greater than zero and the minimum is zero, and

size = log10( value / scale

otherwise.

Number of Decimals

This integer value specifies the number of digits after the decimal point to be used in displaying numeric data values in text format. As such this item is not relevant to Marker style posting.

Marker Index

This index specifies the marker to use for displaying the data value. This index may be any value between 0 and 17, and may be changed using the spin control at the right of the text box, or by clicking on the text box itself to bring up the Marker Selection Menu.

Marker Colour

This box displays the pen colour which will be used to display the data marker. If the colour needs to be changed, click on the colour box to bring up the Pen Colour Specification Menu.

Posting Preview Window

In the lower part of the Post Variable Definition menu is the Posting Preview Window. If the current display area limits and map scale are defined and valid, this window displays the currently defined posting style. As the posting specifications are changed, the suitability of the choices for the parameters can be checked by clicking on the Redraw and the Next and Previous buttons. The x, y and data values are also displayed in the text boxes on the right of the preview window.

Finally the Display Data Range menu is accessible from this menu by clicking on the Display Data Range button at the bottom of the screen.

Any changes made from the menu can be discarded by clicking on the Cancel button, otherwise the changes will be saved if the OK button is clicked.