QGIS
style tools for vector layers allow us to build custom symbols for
archaeological drawings (plans and sections). In this post I will
present some preliminary
examples of customizable styles for graphically representing hachures
and soil texture (clay, silt, sand and so on). For each, the .qml style files are downloadable from http://www.uselessarchaeology.com/ (section programming): you can put them
in your QGIS
project and/or add to QGIS style manager for testing and modifying.
Using
vector styles makes the drawing more automatic and fast, because is
no more necessary to draw manually each individual symbol.
Furthermore, vector styles enable to change quickly the size of
symbols when the scale changes: in such way there is no need to scale
any single object.
The
bulding of a new style is managed by QGIS style window: with
button “Add symbol layer”
is possible to make a new symbol joining 2 or more individual
symbols. All symbols settings (dimension, angle, offset, etc.) can be
changed in the same window.
Hachures
In
plans, the edges of holes and ditches and the differences in level are
represented with hachures. They are composed by an isosceles
triangle and a line: the triangle marks the highest part of the
feature, where the slope begins; the line represents the length and
direction of the slope, with the end of the line showing the bottom
of the slope. I created 3 different styles of hachure for point
layers (hachure_pn), linear layers (hachure_ln) and
polygon layers (hachure_pl).
For
representing the differences in level, for example at the top of
wall, I create a shapefile of points connected to an attribute table
with two numeric columns named “angle” and “length”: the
first column records rotation angle of hachures, the latter records
the length of hachure's lines (where lines are not required, the
column value will be always “0”). Then I draw points in the place
where there are differences in altitude, I load hachure_pn
style,
I rotate each points with “Rotate Point Symbols tool” (in
advanced digitizing toolbar)
and I write the line length I desire in attribute table.
All
settings are customizable: from “Marker – Advanced – Rotation
field” you can set attribute columns
for angle; from
“Vector Field Marker” you can set attribute columns
for angle and length; from “Simple marker” you can set triangle
dimensions and offset: usually I give an offset that is half of
triangle dimension for fitting the point to the line.
Hachure_pn
style can be used also for linear or polygon features.
If
I have to draw a scarp, I create a linear shapefile and I load
hachure_ln style. It's possible to modify dimension of
triangles, space between symbols, width of line, etc. changing
parameters in QGIS style window.
For
representing a ditch or a hole, I create 2 polygon shapefiles, one
for top perimeter of the feature, one for the bottom limits. The top
polygon is drawn by hachure_pl style and the bottom polygon is
filled by white color: in the layer tree the bottom polygon must stay
over the top polygon for covering the hachure's lines that exceed the
slope. Like above, dimensions, space between symbols, offset and so
on are editable in QGIS style window.
Soil
texture
I
post some examples of archaeological layers filled with symbols
representing soil components: clay,
silt, sand, silt-sand.
You
have to pay attention to the settings of the these styles. Many
symbols are set in map units and not in absolute measure (i.e.
millimeters) to better fit the variation of scale during the display.
For printing, all style settings must be changed according to the
plot scale; for this purpose printing tests are recommended. Finally,
I suggest to export in .svg format and modify the layout in Inkscape
for adjusting the last details.
In
future I hope to post other examples of archaeological styles. But if
you have other ideas or you want to contribute with your personal
QGIS archaeological styles, we could create a shared library of
archaeological symbols for QGIS.
Denis Francisci
