mapug.html

m_map是加拿大学者编写的一个在matlab上绘地图的软件

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>
  <pre><a name="p5.3">m_contour(LONG,LAT,VALUES)<br>m_contourf(LONG,LAT,VALUES)<br></a></pre>
  <a name="p5.3">Again, these functions will return handles to graphics
objects, allowing (for example) the drawing of labelled contours: </a>
  <pre><a name="p5.3">[cs,h]=m_contour(LONG,LAT,VALUES)<br>clabel(cs,h,'fontsize',6);<br></a></pre>
  <p> <a name="p5.3">Fancy arrows (i.e. with width, head shape, and
colour specifications) can be generated using <code> m_vec.m </code>.
See the on-line help for more details about the use of <code>m_vec</code>.
  </a></p>
  <p> You can also get hatched areas by calling <code>m_hatch</code>: </p>
  <pre>  m_hatch('single',LONG,LAT,...hatch properties)    % Interior Single Hatches. <br>  m_hatch('cross',LONG,LAT,...hatch properties)     % Interior Crossed Hatches. <br></pre>
Note that this call does not generate the edge lines (an additional <code>m_line</code>
is required for this. In addition, we can speckle the inside edges of
patches using:
  <pre>  <br>  m_hatch('speckle',LONG,LAT,...speckle properties)  % Speckled edges.<br></pre>
See the on-line help and/or <a href="../map.html#12._Speckle">Example
13</a> for more details about using <code>m_hatch</code>.
  <center><a name="p5.3"> <img src="./extspeckle.gif"> </a></center>
  <h3><li><a name="p5.2new"></a>Drawing images and p_color </li>
  </h3>
  <p><a name="p5.4"></a><tt>m_pcolor</tt> is a drop-in replacement for <tt>p_color,</tt>
&nbsp;but you must be careful with its use near map boundaries. Ideally
one would want data to extend up to (but not across) a map boundary
(i.e. polygons are clipped). However, due to the way in which matlab
handles surfaces this is not easily done. Instead - unless you are
using a simple cylindrical or conic projection - you will probably get
a ragged edge for the coloured surface.&nbsp;<br>
  </p>
  <p>There is no <tt>m_image</tt>. the <tt>image()</tt> function
plots data in rectangular pixels only, and in general projected data
will NOT appear as rectangular pixels. If you want to display a large
pixel image on your map, there are several options:<br>
  </p>
  <ol>
    <li>If your georeferenced image is in lat/long coordinates (i.e.
each data row is along a line of constant latitude, each column a line
of
equal longitude), then you can use <tt>m_pcolor</tt> with <tt>shading
flat</tt>. This is reasonably satisfactory (although it can be slow for
large images), but you MUST remember to offset your coordinates by
one-half of the pixel spacing. This is because of the different
behaviors of <tt>p_color</tt> and <tt>image</tt> when given the same
data.&nbsp;</li>
    <ol>
      <li><tt>image</tt> will center the drawn (i,j) pixel on
the (i,j)th entry of the X/Y matrices.&nbsp;</li>
      <li><tt>p_color</tt> with shading flat will draw a panel between
the (i,j),(i+1,j),(i+1,j+1),(i,j+1) coordinates of the X/Y matrices
with a color corresponding to the data value at (i,j). Thus everything
will appear shifted by one half a pixel spacing.</li>
    </ol>
    <p>Satellite data from mid-latitudes is sometime amenable to this
solution. See the <a href="../map.html#satellite_examples">examples of
satellite data manipulation</a>. </p>
    <li> If your figure has already been placed in some projection, and
if you know the exact parameters of that projection, you can probably
use a straight image call and then overplot an M_Map map. For example,
polar satellite images are often in a polar stereographic projection.
In this case you should use m_ll2xy to get the screen coordinates of
the image corners, then use those points in an image() call before
overplotting your data. See in particular <a
 href="../map.html#3._Aerial_photos"> This example </a>.
      <p> HINT - check to see that coastlines overplot to make sure
this is working correctly. </p>
    </li>
  </ol>
  <h3> <a name="p5.4"><li>Drawing tracklines<br>
  </li>
  </a></h3>
  <a name="p5.4"> </a> <a name="p5.4">It is sometimes useful to
annotate lines
representing
the time-varying location of a ship, aircraft, or satellite with time
and date annotations. This can be done using <code> m_track</code>. </a>
  <pre><a name="p5.4">m_proj('UTM','long',[-72 -68],'lat',[40 44]);<br>m_gshhs_i('color','k');<br>m_grid('box','fancy','tickdir','out');<br><br>% fake up a trackline<br>lons=[-71:.1:-67];<br>lats=60*cos((lons+115)*pi/180);<br>dates=datenum(1997,10,23,15,1:41,zeros(1,41));<br><br>m_track(lons,lats,dates,'ticks',0,'times',4,'dates',8,...<br>        'clip','off','color','r','orient','upright');  <br></a></pre>
  <center><a name="p5.4"> <img src="./track1.gif"> </a></center>
  <a name="p5.4"> <br>
See the on-line help for more details about the use of <code>m_track</code>,
and the different options for setting fontsize, tick spacing, date
formats, etc. </a>
  <p> <a name="p5.4">While fiddling with the various parameters, it
is
often handy to be able to erase the plotted tracks without erasing the
coastline and grid. This can be done using </a></p>
  <pre><a name="p5.4">m_ungrid track<br></a></pre>
  <a name="p5.4">or </a>
  <pre><a name="p5.4">m_ungrid('track')<br></a></pre>
  <h3><a name="p5.4"> </a> <a name="p5.5"><li> Drawing range rings
and geodesics</li>
  </a></h3>
  <a name="p5.5">One nifty thing that is sometimes useful is the
ability to draw circles at a given range or ranges from a specific
location. This can be done using <code> m_range_ring</code>, which has
3 required calling parameters: LONG, LAT, RANGE, followed by any number
of (optional) line specification property/value pairs. </a><a
 href="../map.html#e11">Example 11</a> illustrates how to use <code>m_range_ring</code>.
  <p> If you want to plot circular geodesics (i.e. curves which are
perpedicular to
the range rings at all ranges), <code>m_lldist</code> can find both
distances and
points along the geodesics between points. <a href="../map.html#e13">Example
13</a> illustrates how to use <code>m_lldist</code>.<br>
  </p>
  <p>If you care about the difference between great circle and
ellipsoidal geodesics (a very very small proportion of users I would
bet) then <code>m_fdist</code> (which computes the position at a given
range/bearing from another), <code>m_idist</code> (distance and
bearings between points), and <code>m_geodesic</code> (points along
the geodesic) can be used with a variety of (user-specified) ellipses.
The calling sequence for these is different than for <code>m_lldist</code>
for historical reasons.<br>
  </p>
  <h3> <a name="p5.1"><li> Converting longitude/latitude to
projection
coordinates </li>
  </a></h3>
  <a name="p5.1">If you want to use projection coordinates (perhaps
you
want to compute map areas, or distances, or you want to make a legend
in the upper left corner), the following command converts
longitude/latitude coordinates to projection coordinates. </a>
  <pre><a name="p5.1">[X,Y]=m_ll2xy(LONG,LAT, ...optional clipping arguments )<br></a></pre>
  <a name="p5.1">where LONG, LAT, X, and Y are matrices of the same
size. Projection coordinates are equal to true distances near the
center of the map, and are expressed as fractions of an earth radius.
To get a distance, multiply by the radius of the earth (about 6370km).
The exception is the UTM projection which provides coordinates of
northing and easting in meters. </a>
  <p> <a name="p5.1">The possible clipping arguments are </a></p>
  <h4><a name="p5.1"> <code> 'clip','on' </code> </a></h4>
  <a name="p5.1">This is the default. Columns of LONG and LAT are
assumed to form lines, and these are clipped to the map limits. The
first
point outside the map is therefore moved to the map edge, and all other
points are converted the NaN. </a>
  <h4><a name="p5.1"> <code> 'clip','off' </code> </a></h4>
  <a name="p5.1">No clipping is performed. This is sometimes useful
for
debugging purposes. </a>
  <h4><a name="p5.1"> <code> 'clip','point' </code> </a></h4>
  <a name="p5.1">Points are tested against the map limits. Those
outside the limits are converted to NaN, those inside are converted to
projection coordinates. No points are moved. This option is useful for
point data
(such as station locations). </a>
  <h4><a name="p5.1"> <code> 'clip','patch' </code> </a></h4>
  <a name="p5.1">Points are tested against the map limits. Those
outside the limits changed into a point exactly on the limits. Those
inside are converted to projection coordinates. This option may be
useful when trying to draw patches, however it probably won't work
well. </a>
  <h3><a name="p5.1"> </a><a name="p5.2"><li> Converting projection
coordinates to longitude/latitude </li>
  </a></h3>
  <a name="p5.2">Conversion from projection coordinates to
longitude/latitude is straightforward: </a>
  <pre><a name="p5.2">[LONG,LAT]=m_xy2ll(X,Y)<br></a></pre>
  <a name="p5.2">There are no options. </a>
  <h3><a name="p5.2"> </a><a name="p5.6"><li> Computing distances
between points </li>
  </a></h3>
  <a name="p5.6">Geodesic (great circle) distances on a spherical
earth
can be computed between pairs of either geographic (long/lat) or map
(X/Y) coordinates using the functions <code>m_lldist</code> and <code>m_xydist</code>.
For example, </a>
  <pre><a name="p5.6">DIST=m_lldist([20 30],[44 45])<br></a></pre>
  <a name="p5.6">computes the distance from 20E, 44N to 30E, 45N.
Alternatively, if you want to compute the distance between two points
selected by the mouse: </a>
  <pre><a name="p5.6">[X,Y]=ginput(2);<br>DIST=m_xydist(X,Y)<br></a></pre>
  <a name="p5.6">will return that distance. Because of the
inaccuracies
implicit in a spherical earth approximation the true geodesic distances
may differ by 1% or so from the computed distances. </a>
</ol>
<hr>
<h2><a name="p5.6"> </a><a name="p6">6. More complex plots </a> </h2>
<p> For ideas on how to make more complex plots, see the <a
 href="../map.html#examples">Examples</a>. These plots are also
included
in the function <code>m_demo</code>. </p>
<hr>
<h2> <a name="p13">7. Removing data from a plot </a> </h2>
<p> </p>
<p> Once a given map includes several elements a certain amount of
fiddling is usually necessary to satisfy the natural human urge to give
the image a certain aesthetic quality. If the image includes
complicated coastlines which take a long time to draw (e.g. those
discussed below) than clearing the figure and redrawing soon becomes
tedious. The <code>m_ungrid</code> command introduced above can be
used to selectively remove parts of the
figure. For example: </p>
<pre>m_proj('lambert','long',[-160 -40],'lat',[30 80]);<br>m_coast;<br>m_range_ring(-123,49,[1e3:1e3:10e3],'color','r');<br></pre>
draws range rings at 1000km increments from my office. But I am
unsatisfied with this, and want to redraw using only 200km increments.
I can remove the effects of <code>m_range_ring</code> and redraw
using:
<pre>m_ungrid range_ring<br>m_range_ring(-123,49,[200:200:2000],'color','r');<br></pre>
In general the results of <code>m_ANYTHING</code> can be deleted
by calling <code>m_ungrid ANYTHING</code>.
<p> <code>m_ungrid</code> can recognize and delete specific elements
by searching the <code>'tag'</code> property of all plot elements,
which is set by the various different M_Map routines. </p>
<hr>
<h2> <a name="p7">8. Adding your own coastlines </a> </h2>
<p> If you are interested in a particular area and want a
higher-resolution coastline than that used by <code>m_coast</code>,
the best procedure is to </p>
<ol>
  <li> Get a subset of points from some high-resolution database, and </li>
  <li> convert to screen coordinates using <code>m_ll2xy</code>, and
plot. </li>
</ol>
One place where high-resolution coastline data can be obtained is <a
 href="http://rimmer.ngdc.noaa.gov/mgg/coast/getcoast.html"> The
Coastline
Extractor</a>. Follow the instructions there to get coastline data in
a matlab-readable file, and download to your computer. If the file is
saved as "coast.dat", you can plot it (as lines) using the following:
<pre>load coast.dat<br>m_line(coast(:,1),coast(:,2));<br></pre>
Filled coastlines will require more work. You should first read the
instructions there on joining the coastline data into continuous
segments. If you are lucky, (i.e. no lakes or anything else), you <em>may</em>
achieve success with
<pre>load coast.dat<br>[X,Y]=m_ll2xy(coast(:,1),coast(:,2),'clip','patch');<br>k=[find(isnan(X(:,1)))];<br>for i=1:length(k)-1,<br>    x=coast([k(i)+1:(k(i+1)-1) k(i)+1],1);<br>    y=coast([k(i)+1:(k(i+1)-1) k(i)+1],2);<br>    patch(x,y,'r');<br>end;<br></pre>
If this does not work, read the comments in <code>private/mu_coast</code>,
orient the curves in the desired fashion, and use <code>m_usercoast</code>
to load your own data.
<ol>
  <h3> <a name="p7.1"><li><br>
  </li>
  </a> DCW political boundaries </h3>
  <p> Files containing political boundaries for various countries and
US
states can be downloaded from <a href="http://www.maproom.psu.edu/dcw">
http://www.maproom.psu.edu/dcw/</a>. Select an area and choose the
"download
points" option (rather than "download data"). Once downloaded to your
machine
use <code>m_plotbndry</code> to access and plot the desired boundary.
For
example, if you downloaded various US states into a subdirectory
"states:, </p>
  <pre>m_plotbndry('states/arizona','color,'r')<br></pre>
would plot arizona on the current map.
</ol>
<hr>
<h2> <a name="p8">9. Adding your own topography/bathymetry </a> </h2>