[QGIS Commit] r9523 - docs/trunk/english_us/user_guide

[svn_qgis at osgeo.org]

Author: dassau
Date: 2008-10-23 05:15:25 -0400 (Thu, 23 Oct 2008)
New Revision: 9523

Modified:
   docs/trunk/english_us/user_guide/working_with_vector.tex
Log:
added some notes about topological editing as discussed on the mailing list
better described general and layer based snapping function



Modified: docs/trunk/english_us/user_guide/working_with_vector.tex
===================================================================
--- docs/trunk/english_us/user_guide/working_with_vector.tex	2008-10-23 08:57:16 UTC (rev 9522)
+++ docs/trunk/english_us/user_guide/working_with_vector.tex	2008-10-23 09:15:25 UTC (rev 9523)
@@ -782,41 +782,59 @@
 \textbf{Note} - the procedure for editing GRASS layers is different - see
 Section \ref{grass_digitising} for details.
 
-\subsubsection{Setting the Snap Tolerance}
+\subsubsection{Setting the Snapping Tolerance}
 
 Before we can edit vertices, we need to set the snapping tolerance. This is the 
-distance QGIS uses to \usertext{search} for the polygon and vertex you are trying to
-edit when you click on the map. If you aren't within the snap tolerance,
-QGIS won't find and select the vertex for editing. Tolerance is set in map
+distance QGIS uses to \usertext{search} for the closest vertex and/or segment you 
+are trying to connect when you click on the map. If you aren't within the snap tolerance,
+QGIS won't find and select the vertex or/and segment for editing. Tolerance is set in map
 units so you may find you need to experiment to get it set right. If you
-specify too big of a tolerance, QGIS may snap to the wrong vertex,
-especially if you are dealing with a large number of vertices in close
-proximity. Set it too small and it won't find anything and it will pop up an
-annoying warning to that effect. 
+specify too big of a tolerance, QGIS may snap to the wrong vertex, especially if you are 
+dealing with a large number of vertices in close proximity. Set it too small and it won't 
+find anything and it will pop up an annoying warning to that effect. 
 
-To set the snap tolerance, choose \dropmenuopttwo{mActionOptions}{Options} from the
-\mainmenuopt{Settings} menu and click on the \tab{Digitizing} tab.  Remember the
-tolerance is in map units. For our little digitizing project, the units
-are in decimal degrees.  Your results may vary, but something on the order
-of 0.05 to 0.1 should be fine. 
+There are two possibilities to define the snapping tolerance. 
 
-Additionally QGIS supports {\em special} snapping options for every project.
-Therefor you can select \dropmenuopttwo{mActionOptions}{Project
-Properties\dots} from the \mainmenuopt{Settings} menu. The \tab{General} tab
-provides a section \classname{Digitize} where you can \checkbox{Enable
-topological editing} or activate the option \checkbox{Avoid intersections of
-new polygons}. \\
-The button \button{Snapping options\dots} provides the dialog \dialog{Snapping
-options\dots} (see fig. \ref{fig:snappingoptions}) where you can enable and
-adjust the snapping-mode and the tolerance on a layer basis.
+\begin{enumerate}
+\item A general, project wide snapping tolerance can be defined choosing \mainmenuopt{Settings} -> \dropmenuopttwo{mActionOptions}{Options} 
+In the \tab{Digitizing} tab you can select between to vertex, to segment or to vertex and segment 
+as default snap mode. You can also define a default snapping tolerance and a search radius for 
+vertex edits. Remember the tolerance is in layer units. In our digitizing project, the units are 
+in feet. Your results may vary, but something on the order of ?? to ?? should be fine.
+\item A layer based snapping tolerance can be defined coosing \mainmenuopt{Settings} -> 
+\dropmenuopttwo{mActionOptions}{Project Properties\dots}. In the \tab{General} tab, section 
+\classname{Digitize} you can click on \button{Snapping options\dots} to enable and adjust snapping 
+mode and tolerance on a layer basis (see Figure~\ref{fig:snappingoptions}).
+\end{enumerate}
 
 \begin{figure}[H]
    \begin{center}
    \caption{Edit snapping options on a layer basis \nixcaption}\label{fig:snappingoptions}\smallskip
-   \includegraphics[clip=true, width=10cm]{editProjectSnapping} 
+   \includegraphics[clip=true, width=14cm]{editProjectSnapping} 
 \end{center}  
 \end{figure}
 
+\subsubsection{Topological editing}
+
+Besides layer based snapping options the \tab{General} tab in menu \mainmenuopt{Settings} -> \dropmenuopttwo{mActionOptions}{Project Properties\dots} also provides some topological functionalities. 
+In section Digitize you can \checkbox{Enable topological editing} and/or activate 
+\checkbox{Avoid intersections of new polygons}.
+
+\minisec{Enable topological editing}
+
+The option \checkbox{Enable topological editing} is for editing and maintaining 
+common boundaries in polygon mosaics. QGIS "detects" a shared boundary in 
+a polygon mosaic and you only have to move the vertex once and QGIS will take 
+care about updating the other boundary.
+
+\minisec{Avoid intersections of new polygons}
+
+The second topological option called \checkbox{Avoid intersections of new polygons} 
+avoids overlaps in polygon mosaics. It is for quicker digitizing of adjacent polygons. 
+If you already have one polygon, it is possible with this option to digitise the second 
+one such that both intersect and qgis then cuts the second polygon to the common boundary. 
+The advantage is that users don't have to digitize all vertices of the common boundary.
+
 \subsubsection{Editing an Existing Layer}
 \index{vector layers!editing}
 \index{editing!an existing layer}
@@ -1034,7 +1052,6 @@
 
 \minisec{Add Ring}
 \index{vector layers!add!ring}
-\textbf{New since v0.9}
 
 You can create ring polygons using the \toolbtntwo{mActionAddRing}{Add Ring}
 icon in the toolbar. This means inside an existing area it is
@@ -1044,16 +1061,11 @@
 
 \minisec{Add Island}
 \index{vector layers!add!island}
-\textbf{New since v0.9}
 
 You can \toolbtntwo{mActionAddIsland}{add island} polygons to a selected multipolygon. 
 The new island polygone 
 has to be digitized outside the selected multipolygon. 
 
-% FIXME: In versions > 0.9.0 tries to convert a selected normal polygone to a
-% multipolygone, if you try to use the "add island" funtionality. 
-% (not yet implemented)
-
 \minisec{Cutting, Copying and Pasting Features}
 \index{vector layers!cut!feature}
 \index{vector layers!copy!feature}