GRASSベクターレイヤのデジタイズと編集
Digitizing and editing a GRASS vector layer
The digitizing tools for GRASS vector layers are accessed using the
grass_editEdit GRASS vector layer icon on the toolbar. Make
sure you have loaded a GRASS vector and it is the selected layer in the legend
before clicking on the edit tool. Figure <A HREF="#fig:grass_digitizing_category">30</A>
shows the GRASS edit dialog that is displayed when you click on the edit tool.
The tools and settings are discussed in the following sections.
<P>
<IMG
WIDTH="500" HEIGHT="11" ALIGN="BOTTOM" BORDER="0"
SRC="img4.png"
ALT="\begin{Tip}
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\caption{\textsc{Digitizing polygones in ...
...mation of a polygon always to the centroid and not to the
boundary.
}
\end{Tip}">
<P>
Toolbar<A NAME="label_grasstoolbar"></A>
<P>
In Figure <A HREF="#fig:grass_digitizing_toolbar">29</A> you see the GRASS digitizing
toolbar icons provided by the GRASS plugin. Table <A HREF="#tab:grass_tools">3</A>
explains the available functionalities.
<P>
[clip=true,width=12cm]grass_digitizing_toolbar |
<P>
<P>
<A NAME="284"></A>
<A NAME="285"></A>
Icon | Tool | Purpose |
---|---|---|
[width=0.7cm]grass_new_point | New Point | Digitize new point |
[width=0.7cm]grass_new_line | New Line | Digitize new line (finish by selecting new tool) |
[width=0.7cm]grass_new_boundary | New Boundary | Digitize new boundary (finish by selecting new tool) |
[width=0.7cm]grass_new_centroid | New Centroid | Digitize new centroid (label existing area) |
[width=0.7cm]grass_move_vertex | Move vertex | Move one vertex of existing line or boundary and identify new position |
[width=0.7cm]grass_add_vertex | Add vertex | Add a new vertex to existing line |
[width=0.7cm]grass_delete_vertex | Delete vertex | Delete vertex from existing line (confirm selected vertex by another click) |
[width=0.7cm]grass_move_line | Move element | Move selected boundary, line, point or centroid and click on new position |
[width=0.7cm]grass_split_line | Split line | Split an existing line to 2 parts |
[width=0.7cm]grass_delete_line | Delete element | Delete existing boundary, line, point or centroid (confirm selected element by another click) |
[width=0.7cm]grass_edit_attributes | Edit attributes | Edit attributes of selected element (note that one element can represent more features, see above) |
[width=0.7cm]grass_close_edit | Close | Close session and save current status (rebuilds topology afterwards) |
</DIV>
<P> Category Tab<A NAME="307"></A>
<P> The Category tab allows you to define the way in which the category values will be assigned to a new geometry element.
<P>
[clip=true,width=10cm]grass_digitizing_category |
<P>
- Mode: what category value shall be applied to new geometry
elements.
- Next not used - apply next not yet used category value to geometry element.
- Manual entry - manually define the category value for the geometry element in the 'Category'-entry field.
- No category - Do not apply a category value to the geometry element. This is e.g. used for area boundaries, because the category values are connected via the centroid.
- Category - A number (ID) is attached to each digitized geometry element. It is used to connect each geometry element with its attributes.
- Field (layer) - Each geometry element can be connected with several attribute tables using different GRASS geometry layers. Default layer number is 1.
<P>
<IMG
WIDTH="251" HEIGHT="11" ALIGN="BOTTOM" BORDER="0" SRC="img5.png" ALT="\begin{Tip}
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\caption{\textsc{Creating an additional G...
...Table tab
you can create your new table connected to your new layer.
}
\end{Tip}">
<P> Settings Tab<A NAME="label_settingtab"></A><A NAME="329"></A>
<P> The Settings tab allows you to set the snapping in screen pixels. The threshold defines at what distance new points or line ends are snapped to existing nodes. This helps to prevent gaps or dangles between boundaries. The default is set to 10 pixels.
<P>
[clip=true,width=8cm]grass_digitizing_settings |
<P> Symbology Tab<A NAME="339"></A>
<P> The Symbology tab allows you to view and set symbology and color settings for various geometry types and their topological status (e.g. closed / opened boundary).
<P>
[clip=true,width=8cm]grass_digitizing_symbology |
<P> Table Tab <A NAME="349"></A>
<P> The Table tab provides information about the database table for a given 'layer'. Here you can add new columns to an existing attribute table, or create a new database table for a new GRASS vector layer (see Section <A HREF="node9.html#sec:creating_new_grass_vectors">9.6</A>).
<P>
[clip=true,width=10cm]grass_digitizing_table |