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Creating Points and placing Symbols

What are Points and Symbols?

Creating Points and assigning Symbols

Multi-point items

Creating Symbols

Symbols and levels

Creating complex Symbols

Ordnance Survey Symbols (UK specific)

Creating a symbol from an image

Creating Symbols in a Named Object Library

Forcing the Symbol of all Points on an overlay

Symbol Scales

What are Points and Symbols?

Points usually have a symbol assigned to them. A symbol is a pre-defined "graphic". SIS provides a number of pre-defined symbols which are named objects stored in the (standard) library. You can also create your own symbols, which can consist of any group of LineString, Polygon, bitmap, or box text items.

Points can also be seeds for Polygons and TopoLineString items, see Topology.

Creating Points and assigning Symbols

See Point [Create-Simple] for details of creating Points and assigning Symbols.

Multi-point items

A multi-point item is a single item consisting of more than one point, all the constituent point items having the same symbol and style. You can create a multi-point item by first selecting a point item, then using Add Geometry [Create-Edit] to add further points to it.

A multi-point item can be manipulated as a single item. The symbol used to display the points in the multi-point item is that of the original point item (the one to which other point items were added).

Creating Symbols

A symbol may consist of any combination of LineString items, Polygon items, box text and bitmaps (but not point text and topological structures; although you can use these items, they will not be displayed). You can create symbols using Map Editor and Map Modeller.

Open a new, empty SWD.
Select CRS [Home-Map] Viewing Projection tab and change the Viewing Projection to Paper
Create the graphics that make up the symbol. You could use the Create-Simple and Create-Advanced commands, i.e. LineString, Polygon, Rectangle, etc. to create the symbol, or you could use a bitmap. If you are using a bitmap for a logo, you may wish to resize the bitmap using the Move [Edit-Alter-Arrange] Scale entry so that it is the correct size. Use the Measure functions to obtain the correct size. If you are using a bitmap for a symbol, use Insert From File [Create-Miscellaneous] to import the bitmap.
Select all the graphics which make up the symbol.
Select Symbol [Create-Miscellaneous].
Click a position for the centre of the symbol. The centre is the position by which you will later place the symbol. The Save Symbol As dialog will be displayed:
In the Save Symbol As dialog, enter a Folder name if you want to create a new folder (you will need to do this if there are no other symbols in the enabled libraries), or select an existing folder name if appropriate. All symbol folders in all enabled libraries are listed.
Enter a Name for the symbol. Symbols are named objects, see Named Objects, the symbol is then stored in the current library:
If you wish, you may delete the graphics used to form the symbol, as these are no longer required.

Symbols and levels

When symbols are drawn on Points, the levels are added together. SIS will only draw levels between 0 and 255. If the total of the levels is greater than 255 the symbol is not drawn.

When arriving at a total number for the levels each individual layer of the Symbol is taken into account.

The following examples illustrate this:

It is recommended that items making up a symbol are set to a low level to avoid the possibility of all, or part, of the symbol not being displayed.

To ensure the Symbol is displayed at the correct scale set the _pointScaleOverride# property to -1, this is described in Fixing the Symbol size.

Creating complex Symbols

Symbols can be extremely complex objects, making extensive use of the advanced capabilities of SIS such as scale thresholds and levels. For example, it is possible to create symbols which appear differently at different scale thresholds.

Ordnance Survey Symbols (UK specific)

Ordnance Survey files contain locations for symbols of ordnance benchmarks, pylons, flow arrows, etc. These Ordnance Survey symbols are stored with appropriate names (e.g. Bench Mark, Pylon, Flow Arrow) in the OS DNF, OS NTF and OSNI NTF folders in the (standard) library.

Creating a symbol from an image

Note: Make sure that the Brush is set to Blank to make transparency work.

Set the Map Window Coordinate Reference System to Paper.
Select Insert from File [Create-Miscellaneous].

When you bring an image into a map window, it is resized to fit the current viewed area. An easy way to create the symbol at the appropriate size is to zoom in first, then use Insert from File [Create-Miscellaneous].

Methods to zoom in to the correct scale:

Create a square, with the dimensions of the size you require the symbol to be – i.e. with equal x and y of 0.01m (10mm). Zoom extents, and delete it.

or

Drop an existing symbol of the right size down i.e. circle, right click explode, zoom extents. This zooms in to the appropriate scale.
Right click, select Properties, or use the Format tab, to set the Pen and Brush to be Blank. This will enable the transparency function if used and remove the outline.

Note: Some image formats support transparency, i.e. GIF, PNG, TIFF, either through a transparent color or an alpha channel. Transparency can be set in a graphics package before inserting the image in to SIS.
Create the Symbol and save in a NOL.

Creating Symbols in a Named Object Library

To create a Symbol in a Named Object Library:

Draw the graphics as normal items in the way you wish the Symbol to appear.
Select those items, and then use Symbol [Create-Miscellaneous].
Enter the origin for the symbol and its name.

When you place a copy of a Symbol using a Point item there is an interaction between the properties of the Point item and the properties of the item(s) which define the Symbol. In general the properties of the item take priority, unless they are undefined. Properties that act in this way include Pen, Brush, Minimum scale, and Maximum scale.

This means that if the original items have the "(By Overlay)" Pen, then they will be drawn in the Pen of the Point item. But if the original items have their own Pen objects, then the Pen of the Point item will be ignored. If the Pen objects of the items are mixed between "(By Overlay)" and other Pen objects, then the effect of changing the Point item’s Pen will be to partially change the Pen objects used to draw the Symbol.

The Level of the original items determines the drawing order of the components of the Symbol every time it is drawn. This means that you can define a Symbol made up of Polygon items that use opaque Brush objects. By carefully setting the Level of the Polygon items you can ensure that you get the overlapping effect that you want. Using Polygon items (or Bitmap items) in Symbol objects is especially useful for symbols that stand out, e.g. for Command and Control type applications.

Forcing the Symbol of all Points on an overlay

This is similar to setting the (By Overlay) symbol (see above), except that this procedure makes all points on the overlay use the selected symbol, not just those which use the (By Overlay) symbol.

In the Overlays dialog, select the Styles tab.
Select the overlay for which you want to force the symbol.
Click on the required symbol in the Symbol drop-down list.
Tick the Override checkbox.
Click OK.

Symbol Scales

All Symbol objects are defined in Named Object Libraries using paper units. That means that they know how big they should be printed on paper, and their size on screen must be recalculated each time they are drawn.

When you create a Symbol the current viewing scale is used to convert the items from world units into paper units. Then when you place Point items which use that Symbol, the Point item’s dataset scale is used to convert from paper units back to world units. The net result is that the placed Symbol objects appear the same size as the original graphics unless the dataset scale is different to the original view scale.

You can modify the size of a Symbol, by setting the Scale property, which has a default value of 1 (one).

By default SIS assumes that you will print the current SIS Workspace Definition (SWD) onto paper at the current viewing scale, so it shows you how big the Symbol objects will be relative to other graphics (like roads and buildings). This means that the Symbol objects will change size on screen as you zoom in and out.

However, some applications are more interested in how the graphics appear on screen than on how they will appear on paper. An example is a Command and Control system where moving objects like cars are tracked on screen. In this case you can use a negative Scale. A Scale of -1 will cause the Symbol to be drawn at its Named Object Library size on screen, regardless of how much you zoom in or out.

When the effective viewing scale is the same as the dataset scale, a negatively scaled Symbol will appear the same as a positively scaled Symbol (so -2.5 would be the same as +2.5).

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