Symbolizer that specifies rendering of a png, tiff, or svg graphic symbol and label text at a point.
Effectively, this is a (working) combination of TextSymbolizer and PointSymbolizer. If you try to use a TextSymbolizer and a PointSymbolizer separated you will often see points without texts and/or texts without points.
Configuration Options
Supports all options of TextSymbolizer with additional options:
| parameter | value | default |
|---|---|---|
| base | Base symbol template (See below) | |
| file | The file to use for the shield background | |
| opacity | opacity of the image used for the shield | 1 |
| text-opacity | opacity of the text placed on top of the shield | 1 |
| unlock-image | If true the shield image doesn't move | "false" |
| shield-dx | offset the shield image and text horizontally | 0 |
| shield-dy | offset the shield image and text vertically | 0 |
| transform | Transform image |
base
Add
<FileSource name="foo">/home/bar/baz/</FileSource>
to the beginning of your stylesheet and then use
<ShieldSymbolizer base="foo" name="bridge" />
to refer to /home/bar/baz/bridge.
dx, dy
To draw labeled points configure placement="point" (which is the default) and set dx/dy to move the text.
dx, dy from TextSymbolizer moves only the text, and not the shield. This behavior will be changed in a future release of mapnik. (See below).
New interface in HarfBuzz branch
| parameter | value | default |
|---|---|---|
| shield-dx, shield-dy | Move shield only. | 0 |
| dx, dy | With unlock_image = true: move text only. | 0 |
| With unlock_image = false: move text and shield | 0 | |
| unlock_image | True: Shield base point is always the input line/point (usecase: labeling bus stations). | 0 |
| False: Shield base point is the center of the text (i.e. depends on dx,dy,vertical-alignment, horizontal-alignment) (usecase: highway shields) |
When symbols are still moving with dx/dy after setting unlock_image = true, try unlock-image="true" instead.
placement
placement="line" only means placement along a line for ShieldSymbolizer, whereas for TextSymbolizer it rotates the text too. Add the spacing parameter to get the ShieldSymbolizer to repeat along the line, otherwise placement="line" and placement="point" will look the same.
Examples
Setting up a sample shield symbolizer, from the Cascade Users of OpenSource GeoSpatial (CUGOS) list: http://groups.google.com/group/cugos/browse_thread/thread/b62b4890e1933bba
XML
<ShieldSymbolizer
face-name="DejaVu Sans Bold" size="6" fill="#000000"
file="images/shield.svg" spacing="100" transform="scale(2.0,2.0)"
min-distance="50">
[NAME]
</ShieldSymbolizer>
Python (Mapnik 2)
shield = ShieldSymbolizer(Expression('[NAME]'),'DejaVu Sans Bold',6,Color('#000000'),PathExpression('images/ushighway_shield_20.png'))
shield.min_distance = 50
shield.label_spacing = 100
shield.displacement = (dx,dy)
Python (Mapnik 3)
No support.
C++
rule_type rule;
/* Parameters:
name
face name
size
color
image
image type
width
height
*/
shield_symbolizer ss("[NAME]", "DejaVu Sans Bold", 6, color(0, 0, 0), "/path/to/icon.png", "png", 20, 20);
ss.set_label_placement(mapnik::LINE_PLACEMENT); // Place label along the line
ss.set_displacement(dx, dy);
ss.set_label_spacing(min_distance);
rule.append(ss);
Resources
http://www.routemarkers.com/
http://www.weait.com/content/badges-badges