[QGIS Commit] r11260 - in docs/trunk/english_us/user_guide: . working_with_vector_screenies

[svn_qgis at osgeo.org]

Author: dassau
Date: 2009-08-04 02:52:36 -0400 (Tue, 04 Aug 2009)
New Revision: 11260

Added:
   docs/trunk/english_us/user_guide/working_with_vector_screenies/vectorNotWrapping.png
   docs/trunk/english_us/user_guide/working_with_vector_screenies/vectorWrapping.png
Modified:
   docs/trunk/english_us/user_guide/qgis_style.sty
   docs/trunk/english_us/user_guide/working_with_vector.tex
   docs/trunk/english_us/user_guide/working_with_vector_screenies/Makefile
Log:
added patch from Giovanni Manghi that describes a solution to display vector layers crossing 180?\194?\176 longitude


Modified: docs/trunk/english_us/user_guide/qgis_style.sty
===================================================================
--- docs/trunk/english_us/user_guide/qgis_style.sty	2009-08-04 01:56:20 UTC (rev 11259)
+++ docs/trunk/english_us/user_guide/qgis_style.sty	2009-08-04 06:52:36 UTC (rev 11260)
@@ -28,6 +28,9 @@
 \renewcommand{\sfdefault}{phv}  % switch \sf to Helvetica T1
 \renewcommand*{\familydefault}{\sfdefault} 
 
+% new command to display degree sign
+\newcommand\degrees[1]{\ensuremath{#1^\circ}}
+
 % new command to suppress appendix captions
 \def\afterfi#1\fi{\fi#1}
 \let\ORIGaddtocontents\addtocontents

Modified: docs/trunk/english_us/user_guide/working_with_vector.tex
===================================================================
--- docs/trunk/english_us/user_guide/working_with_vector.tex	2009-08-04 01:56:20 UTC (rev 11259)
+++ docs/trunk/english_us/user_guide/working_with_vector.tex	2009-08-04 06:52:36 UTC (rev 11260)
@@ -424,6 +424,56 @@
 gsherman at madison:~/current$
 \end{verbatim}
 
+\subsubsection{Vector layers crossing 180$^\circ$ longitude}
+\index{vector layers!crossing}
+
+Many GIS packages don't wrap vector maps, with a geographic reference system
+(lat/lon), crossing the \degrees{180} longitude line. As result, if
+we open such map in QGIS, we will see two far, distinct locations, that
+should show near each other. In Figure \ref{fig:vector_not_wrapping} the tiny
+point on the far left of the map canvas (Chatham Islands), should be within
+the grid, right of New Zealand main islands.
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Map in lat/lon crossing the \degrees{180} longitude line
+   \nixcaption}
+   \label{fig:vector_not_wrapping}\smallskip
+   \includegraphics[clip=true, width=\textwidth]{vectorNotWrapping}
+\end{center}
+\end{figure}
+
+A workaround is to transform the longitude values using PostGIS and the
+\textbf{ST\textunderscore Shift\textunderscore Longitude}
+\footnote{\url{http://postgis.refractions.net/documentation/manual-1.4/ST_Shift_Longitude.html}}
+function. This function reads every point/vertex in every component of every
+feature in a geometry, and if the longitude coordinate is < \degrees{0} adds
+\degrees{360} to it. The result would be a \degrees{0} - \degrees{360} version of
+the data to be plotted in a \degrees{180} centric map.
+
+\begin{figure}[ht]
+   \begin{center}
+   \caption{Map crossing the \degrees{180} longitude line
+after applying the \textbf{ST\textunderscore Shift\textunderscore Longitude}
+function}
+\label{fig:vector_wrapping}\smallskip
+   \includegraphics[clip=true, width=9cm]{vectorWrapping}
+\end{center}
+\end{figure}
+
+\minisec{Usage}
+
+\begin{itemize}
+\item Import data to PostGIS (\ref{sec:loading_postgis_data}) using for
+example the PostGIS Manager plugin or the SPIT plugin
+\item Use the PostGIS command line interface to issue the following command
+(this is an example where "TABLE" is the actual name of your PostGIS table) \\ 
+\texttt{gis\_data=\# update TABLE set the\_geom=ST\_shift\_longitude(the\_geom);} 
+\item If everything went right you should receive a confirmation about the
+number of features that were updated, then you'll be able to load the map and
+see the difference (Figure \ref{fig:vector_wrapping})
+\end{itemize}
+
 \subsection{SpatiaLite Layers} 
 \index{SpatiaLite layers!properties dialog}
 \index{vector layers!SpatlaLIte|see{SpatiaLite}}

Modified: docs/trunk/english_us/user_guide/working_with_vector_screenies/Makefile
===================================================================
--- docs/trunk/english_us/user_guide/working_with_vector_screenies/Makefile	2009-08-04 01:56:20 UTC (rev 11259)
+++ docs/trunk/english_us/user_guide/working_with_vector_screenies/Makefile	2009-08-04 06:52:36 UTC (rev 11260)
@@ -24,6 +24,8 @@
     queryBuilder.eps \
     addvectorlayerdialog.eps\
     vectorAttributeTable.eps\
+    vectorNotWrapping.eps\
+    vectorWrapping.eps\
 
 # digitising_attributes09.eps\
 #	newvectorlayer.eps\

Added: docs/trunk/english_us/user_guide/working_with_vector_screenies/vectorNotWrapping.png
===================================================================
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Property changes on: docs/trunk/english_us/user_guide/working_with_vector_screenies/vectorNotWrapping.png
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Added: svn:mime-type
   + application/octet-stream

Added: docs/trunk/english_us/user_guide/working_with_vector_screenies/vectorWrapping.png
===================================================================
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Property changes on: docs/trunk/english_us/user_guide/working_with_vector_screenies/vectorWrapping.png
___________________________________________________________________
Added: svn:mime-type
   + application/octet-stream