mapug.html

A mapping package for Matlab:这是一款功能十分强大的地理绘图工具包

subplot(122);<br>
m_coord('geographic');&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;
&nbsp; % Define all in geographic<br>
m_proj('stereographic');<br>
m_coast;<br>
m_grid;<br>
m_line(lon,lat,'color','c');<br>
m_coord('IGRF2000-geomagnetic'); % Now assume that values are in
geomagnetic<br>
m_line(lon,lat,'color','r');</code><br>
  <br>
  <br>
  </a></p>
  <a name="p2.7"> </a>
  <p><a name="p2.7"> </a><a name="p2.6">Note that this option is not
used very much, hence is not fully supported. In particular, filled
coastlines may not work properly. </a></p>
</ol>
<a name="p2.7"> </a>
<hr><a name="p2.7"><br>
<br>
</a>
<h2> <a name="p3"> 3. Coastlines and Bathymetry </a> </h2>
<p> M_Map includes two fairly simple databases for coastlines and
global elevation data. Highly-detailed databases are not included in
this release because they are a) extremely large and b) extremely
time-consuming to
process (loops are inherently involved). If more detailed maps are
required,
<a href="#p9"> section 9 </a> and <a href="#p9.5"> section 10 </a>
give instructions on how to add some freely-available high-resolution
datasets. Read <a href="#p7"> section 7 </a> and <a href="#p8">
section 8 </a> if you want to add your own coastline/bathymetry data. </p>
<ol>
  <h2> <a name="p3.1"> <li> Coastline options </li>
  </a> </h2>
  <p> M_Map includes a 1/4 degree resolution coastline database. This
is suitable for maps covering large portions of the globe, but is
noticeably coarse for many large-scale applications. Users not
satisfied with their regional map are directed to <a href="#p7">
section 7 </a> and/or <a href="#p9.5"> section 10 </a> for more
information on creating and using high-resolution coastlines. The M_Map
database is accessed using the <code> m_coast </code> function.
Coastlines can be drawn as simple lines,
using </p>
  <pre>m_coast('line', ...optional line arguments );<br></pre>
or
  <pre>m_coast( optional line arguments );<br></pre>
where the optional arguments are all the standard arguments for
specifying line style, width, color, etc. Coastlines can also be drawn
as filled
patches using
  <pre>m_coast('patch', ...optional patch arguments );<br></pre>
where the optional trailing arguments are the standard patch
properties. For example,
  <pre>m_coast('patch',[.7 .7 .7],'edgecolor','g');<br></pre>
draws gray land, outlined in green. When patches are being drawn, lakes
and inland seas are given the axes background colour.
  <p> Many older (ocean) maps are created with speckled land
boundaries, which looks
very nice in black and white. You can get a speckled boundary with </p>
  <pre>m_coast('speckle', ....optional m_hatch arguments);<br></pre>
which calls <code>m_hatch</code>. This only looks nice if there aren't
too many
very tiny islands and/or lakes in the image (see <a
 href="../map.html#12._Speckle">Example 13</a>).
  <p> Note that line coastlines are usually drawn rather rapidly.
Filled
coastlines take considerably more time to generate (because map limits
are
not necessarily rectangular, clipping must be accomplished in m-files).
  </p>
  <h2> <a name="p3.2"> <li> Topography/Bathymetry options </li>
  </a> </h2>
  <p> M_Map can access a 1-degree resolution global elevation database
(actually, this database is is included in the Matlab distribution,
used by of <code>$MATLAB/toolbox/matlab/demos/earthmap.m</code>). A
contour map of elevations at default levels can be drawn using </p>
  <pre>m_elev;<br></pre>
Different levels can also be specified:
  <pre>m_elev('contour',LEVELS, optional contour arguments);<br></pre>
For example, if you want all the contours to be dark blue, use:
  <pre>m_elev('contour',LEVELS,'edgecolor','b');<br></pre>
Filled contours are also possible:
  <pre>m_elev('contourf',LEVELS, optional contourf arguments);<br></pre>
Finally, if you want to simply extract the elevation data for your own
purposes,
  <pre>[Z,LONG,LAT]=m_elev([LONG_MIN LONG_MAX LAT_MIN LAT_MAX]);<br></pre>
returns rectangular matrices for depths Z at locations LONG,LAT.
</ol>
<hr>
<h2> <a name="p4"> 4. Customizing axes </a> </h2>
<p> </p>
<ol>
  <h3> <a name="p4.1"><li> Grid lines and labels </li>
  </a></h3>
  <a name="p4.1">In order to get the perfect grid, you may want to
experiment with different grid options. Two functions are useful here,
M_GRID which draws a grid, and M_UNGRID which erases the current grid
(but
leaves all coastlines and user-specified data alone). Try </a>
  <pre><a name="p4.1">m_proj('Lambert');<br>m_coast;<br>m_grid;<br></a></pre>
  <a name="p4.1">to get a Lambert conic projection of North America.
Now try </a>
  <pre><a name="p4.1">m_ungrid<br></a></pre>
  <a name="p4.1">The coastline is still there, but the grid has
disappeared and the axes shows raw X/Y projection coordinates. Now, try
this: </a>
  <pre><a name="p4.1">m_grid('xtick',10,'tickdir','out','yaxislocation','right','fontsize',7);<br></a></pre>
  <a name="p4.1">The various options that can be changed are: </a>
  <h4><a name="p4.1"> <code> 'box',( 'on' | 'off' | 'fancy' ) </code>
  </a></h4>
  <a name="p4.1">This specifies whether or not an outline box is drawn.
Three types of outline boxes are available: <code>'on'</code>, the
default, is a a simple line. Two types of fancy outline boxes are
available. If <code>'tickdir'</code> is <code>'in'</code>, then
alternating black and white patches are made (see </a><a
 href="../map.html#e2">example 2</a>). If <code>'tickdir'</code> is
set to <code>'out'</code>, then a more complex line pattern is drawn
(see <a href="../map.html#e6">example 6</a>). Fancy boxes are in
general only available for maps bounded by lat/long limits (i.e. not
for azimuthal projections), but if this option is chosen
inappropriately a warning message is issued.
  <h4> <code> 'xtick',( num | [value1 value2 ...])</code> </h4>
This specifies the number/location of the longitude grid. If a single
number is specified, grid lines/values are drawn for approximately that
number of equally-spaced locations (the number is only approximate
because the M_GRID attempts to find "nice" intervals, i.e. it rounds to
even increments). Exact locations can be specified by using a vector of
location values. There is an analagous <code> 'ytick' </code>
property.
  <h4> <code> 'xticklabels',[label1;label2 ...]</code> </h4>
Special labels can be specified. Labels can either be numerical values
(which are then formatted by M_GRID), or string values which are used
without change. There is an analagous <code> 'yticklabels' </code>
property
  <h4> <code> 'xlabeldir', ( 'middle' | 'end' )</code> </h4>
Longitude labels are either middled onto the ends of their prespective
grid lines (and drawn perpendicular to those lines), or are drawn
extending outwards fro the ends of those lines. There is an analagous <code>
'ylabeldir' </code> property.
  <h4> <code> 'ticklen',value</code> </h4>
Specifies the length of tickmarks (as a fraction of plot width)
  <h4> <code> 'tickdir',( 'in' | 'out' )</code> </h4>
Specifies whether tickmarks point inwards or outwards. If <code>'box'</code>
is set to <code>'fancy'</code>, this specifies the form of the fancy
outline box.
  <h4> <code> 'color',colorspec <br>
'linewidth', value <br>
'linestyle', ( linespec | 'none' ) <br>
'fontsize',value <br>
'fontname',name</code> </h4>
Specify various line/text properties for the grid and its labels.
  <h4> <code> 'XaxisLocation',( 'bottom' | 'middle' | 'top' ) </code></h4>
Specifies where the X-axis will be drawn, either at the bottom
(southermost) end, at the top (northernmost) end, or in the middle.
  <h4> <code> 'YaxisLocation',( 'left' | 'middle' | 'right' ) </code>
  </h4>
Specifies where the Y-axis will be drawn, either at the left
(westernmostmost) end, at the right (easternmost) end, or in the
middle.
  <h3> <a name="p4.2"><li> Titles and x/ylabels </li>
  </a></h3>
  <a name="p4.2">Titles and x/ylabels can be added to maps using the <code>title</code>
and <code>x/ylabel</code> functions in the usual
way (this is a change from v1.0 in which the 'visible' property had to
be
explicitly set to 'on'; this is now done within m_grid). </a>
  <h3><a name="p4.2"> </a><a name="p4.3"><li> Legend Boxes </li>
  </a></h3>
  <a name="p4.3">A legend box can be added to the map using <code>m_legend</code>.
Only some of the functionality of <code>legend</code> is currently
included. The legend box can be dragged and dropped using the mouse
button. </a>
</ol>
<hr>
<h2><a name="p4.3"> </a><a name="p5">5. Adding your own data </a> </h2>
<p> The purpose of this package is to allow you to map your own data!
Once a suitable grid and (possibly) a coastline have been chosen, you
can add your own lines, text, or contour plots using built-in M_Map
drawing functions which handle the conversion from longitude/latitude
coordinates to projection coordinates. These drawing functions are very
similar to the standard Matlab plotting functions, and are described in
the <a href="#p5.3">next section</a>. </p>
<p> Sometimes you may want to convert between longitude/latitude and
projection coordinates without immediately plotting the data. This
might happen if you want to interactively select points using <code>ginput</code>,
or if you want to draw labels tied to a specific point on the screen
rather than a particular longitude/latitude. Projection conversion
routines are described in sections <a href="#p5.1">5.2</a> and <a
 href="#p5.2">5.3</a>. Once raw longitude/latitude coordinates are
converted into projection coordinates, standard Matlab plotting
functions can be used. </p>
<p> Maps are drawn to fit within the boundaries of the plot axes. Thus
their scale is somewhat arbitrary. If you are interested in making a
map to
a given scale, e.g. 1:200000 or something like that, you can do so by
using the <code>m_scale</code> primitive, see <a href="#p2.6">
section 2.6
</a>. The data units are the projection coordinates, which are
distances
expressed as a fraction of earth radii. To get a map "distance" between
two points, use the Cartesian distance between the points in the
projection
coordinate system and multiply by your favourite value for the earth's
radius, usually around 6370 km (exception - the UTM projection uses
coordinates
of northing and easting in meters, so no conversion is necessary). </p>
<p> Caution: One problem that sometimes occurs is that data does not
appear on the plot due to ambiguities in longitude values. For example,
if plot longitude limits are [-180 180], a point with a longitude of,
say, 200,
may not appear in cylindrical and conic projections. This is not a bug.
Handling the clipping in "wrapped around" curves requires adding points
(rather than just moving them) and is therefore incompatible with
various
other requirements (such as keeping input and output matrices the same
size
in the conversion routines described below). </p>
<ol>
  <h3> <a name="p5.3"><li> Drawing lines, text, arrows, patches,
hatches, speckles and
contours </li>
  </a></h3>
  <a name="p5.3">For most purposes you do not need to know what the
projection coordinates actually are - you just want to plot something
at a specified longitude/latitude. Most of the time you when you want
to plot something on a map you want to do so by specifying
longitude/latitude coordinates, instead of the usual X/Y locations. To
do so in M_Map, replace calls to <code> plot, line, text, quiver,
patch, contour, and contourf </code> with M_Map equivalents that
recognize lontgitude/latitude coordinates by prepending "m_" to the
function name. For example, </a>
  <pre><a name="p5.3"><br>  m_plot(LONG,LAT,...line properties)   % draw a line on a map (erase current plot) <br>  m_line(LONG,LAT,...line properties)   % draw a line on a map <br>  m_quiver(LONG,LAT,U,V,S)              % A quiver plot <br>  m_text(LONG,LAT,'string')             % Text <br>  m_patch(LONG,LAT,..patch properties)  % Patches. <br>  </a></pre>
  <a name="p5.3">Each of these functions will handle the coordinate
conversion internally, and will return a vector of handles to the
graphic objects if desired. The only difference between these functions
and the
standard Matlab functions is that the first two arguments MUST be
longitude
and latitude. </a>
  <p> <a name="p5.3">One caveat applies to <code>m_patch</code>. For
compatibility reasons this uses the same code that applies to coastline
filling. Coastlines come either as either "islands" or "lakes", and
M_Map keeps track of the difference by assuming curves are oriented so
that the filled area ("land") is always on the right as we go around
the curve. This is slightly different than the convention used in <code>patch</code>
which always fills the inside. Keeping track of this difference is
relatively straightforward in a Cartesian system, but not so easy in
spherical coordinates. In the absence of other information <code>m_patch</code>
tries to do the right thing, but (especially when the patch intersects
a map boundary) it can get confused. If a patch isn't filling
correctly, try reversing the order of points using <code>flipud</code>
or <code>fliplr</code>. </a></p>
  <p> <a name="p5.3">Data gridded in longitude and latitude can also
be contoured: </a></p>