graphicprimitive2d.html

Geotools是一个开源的Java GIS工具包,可利用它来开发符合标准的地理信息系统。Geotools提供了OGC(Open Geospatial Consortium)规范的一个实现来作为他们的

        graphicCRS,
        context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#objectiveCRS"><CODE>objectiveCRS</CODE></A> )</code></b><br>
     Returns a transform from the underlying CRS to the rendering CRS.</p></li>

 <li><p><b><code>context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#getMathTransform(org.opengis.referencing.crs.CoordinateReferenceSystem, org.opengis.referencing.crs.CoordinateReferenceSystem)"><CODE>getMathTransform</CODE></A>(
        context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#objectiveCRS"><CODE>objectiveCRS</CODE></A>,
        context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#displayCRS"><CODE>displayCRS</CODE></A> )</code></b><br>
     Returns a transform from the rendering CRS to the <cite>Java2D</cite> CRS in
     "dots" units (usually 1/72 of inch). This transformation is zoom dependent.</p></li>
 </ul>
 
 By default, painting is done in the <cite>Java2D</cite> user space (a.k.a.
 <A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#displayCRS">display CRS</A>. However, the CRS can
 easily be switched. An implementation may looks like as below:

 <blockquote><code>
 <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/awt/Graphics2D.html" title="class or interface in java.awt">Graphics2D</A> graphics =
 context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#getGraphics()">getGraphics()</A>;<br>

 context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#setGraphicsCRS(org.opengis.referencing.crs.CoordinateReferenceSystem)">setGraphicsCRS</A>(context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#objectiveCRS">objectiveCRS</A>);<br>

 // </code>NOTE: Skip the above line if you want to perform the rendering in<code><br>

 // </code>the default <cite>Java2D</cite> user space (a.k.a.
 <A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#displayCRS"><CODE>displayCRS</CODE></A>) rather than<code><br>

 // </code>in terms of "real world" units.<code><br>

 try {<br>

 &nbsp;&nbsp;&nbsp;&nbsp;
 // </code><cite>Paint here map features in geographic coordinates (usually meters or
 angular degrees).</cite><code><br>

 &nbsp;&nbsp;&nbsp;&nbsp;
 context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#addPaintedArea(java.awt.Shape)">addPaintedArea</A>(...);<br>

 &nbsp;&nbsp;&nbsp;&nbsp;
 context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#setGraphicsCRS(org.opengis.referencing.crs.CoordinateReferenceSystem)">setGraphicsCRS</A>(context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#displayCRS">displayCRS</A>);<br>

 &nbsp;&nbsp;&nbsp;&nbsp;
 // </code><cite>Write here texts or labels. Coordinates are in <u>dots</u>.</cite><code><br>

 &nbsp;&nbsp;&nbsp;&nbsp;
 context.<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#addPaintedArea(java.awt.Shape)">addPaintedArea</A>(...);<br>

 } finally {<br>

 &nbsp;&nbsp;&nbsp;&nbsp;
 // </code><cite>Restore here <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/awt/Graphics2D.html" title="class or interface in java.awt"><CODE>Graphics2D</CODE></A> it its initial state.</cite><code><br>

 }<br>
 </code></blockquote>

 During the rendering process, implementations are encouraged to declare a (potentially
 approximative) bounding shape of their painted area with calls to
 <A HREF="../../../../org/geotools/display/canvas/RenderingContext.html#addPaintedArea(java.awt.Shape)"><CODE>RenderingContext.addPaintedArea(Shape)</CODE></A>. This is an optional operation: providing
 those hints only help <A HREF="../../../../org/geotools/display/canvas/BufferedCanvas2D.html" title="class in org.geotools.display.canvas"><CODE>BufferedCanvas2D</CODE></A> to speed up
 future rendering and events processing.
<P>
<DD><DL>
<DT><B>Parameters:</B><DD><CODE>context</CODE> - Information relatives to the rendering context. This object contains the
         <A HREF="http://java.sun.com/j2se/1.4/docs/api/java/awt/Graphics2D.html" title="class or interface in java.awt"><CODE>Graphics2D</CODE></A> to use and methods for getting <CODE>MathTransform</CODE> objects.
<DT><B>Throws:</B>
<DD><CODE>TransformException</CODE> - If a coordinate transformation failed during the rendering
         process.</DL>
</DD>
</DL>
<HR>

<A NAME="prefetch(org.geotools.display.canvas.RenderingContext)"><!-- --></A><H3>
prefetch</H3>
<PRE>
protected void <B>prefetch</B>(<A HREF="../../../../org/geotools/display/canvas/RenderingContext.html" title="class in org.geotools.display.canvas">RenderingContext</A>&nbsp;context)</PRE>
<DL>
<DD>Hints that this graphic might be painted in the near future. Some implementations may
 spawn a thread to compute the data while others may ignore the hint. The default
 implementation does nothing.
<P>
<DD><DL>
<DT><B>Parameters:</B><DD><CODE>context</CODE> - Information relatives to the rendering context. This object contains
         methods for querying the area to be painted in arbitrary coordinate reference system.<DT><B>See Also:</B><DD><A HREF="http://java.sun.com/products/java-media/jai/forDevelopers/jai-apidocs/javax/media/jai/PlanarImage.html#prefetchTiles(java.awt.Point[])" title="class or interface in javax.media.jai"><CODE>PlanarImage.prefetchTiles(java.awt.Point[])</CODE></A></DL>
</DD>
</DL>
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