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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2009-11-02 16:35:15 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2009-11-02 16:35:15 +0000 |
| commit | 3ecef916112c7c8ad5ea741712931ebc95716deb (patch) | |
| tree | f4779cb2095dc9169e34c34739262303fab96c27 /pnmmercator.html | |
| parent | e3be234154b73b18a386d2f69c9f5002f220ce88 (diff) | |
| download | netpbm-mirror-3ecef916112c7c8ad5ea741712931ebc95716deb.tar.gz netpbm-mirror-3ecef916112c7c8ad5ea741712931ebc95716deb.tar.xz netpbm-mirror-3ecef916112c7c8ad5ea741712931ebc95716deb.zip | |
"miscellaneous update"
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@1010 9d0c8265-081b-0410-96cb-a4ca84ce46f8
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diff --git a/pnmmercator.html b/pnmmercator.html new file mode 100644 index 00000000..404e6619 --- /dev/null +++ b/pnmmercator.html @@ -0,0 +1,139 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<html> +<head> +<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1"> +<title>PnmMercator User Manual</title> +</head> +<body> +<h1>pnmmercator</h1> +Updated: October 2009 +<br> +<a href="#index">Table Of Contents</a> + +<h2>NAME</h2> + +pnmmercator - transform a worldmap from rectangular projection to Mercator +projection and vice-versa + +<h2 id="synopsis">SYNOPSIS</h2> +<b>pnmmercator</b> +[<b>-inverse</b>] +[<b>-nomix</b>] +[<b>-[v]verbose</b>] +[<b><i>filename</i></b>] + +<p>Minimum unique abbreviation of option is acceptable. +You may use double hyphens instead of single hyphen to denote options.</p> + +<h2 id="description">DESCRIPTION</h2> + +<p>This program is part of <a +href="http://netpbm.sourceforge.net/doc/index.html">Netpbm</a>.</p> + +<p>The <b>pnmmercator</b> utility, converts a rectangular projection worldmap +to a Mercator projection format, as used for maps.google.com and many other +online maps. The map used as input for <b>pnmmercator</b> must have rows for +-90 to 90 degrees latitude and columns for -180 to +180 degrees longitude. The +file will typically be twice as wide as high, but this is not a +requirement. The output file will be using the <a +href="http://en.wikipedia.org/wiki/Mercator_projection">Mercator +projection</a> and will get double the height of the input file.</p> + +<p>Maps using the Mercator projection are stretched more the closer a row is +to the North or South Pole. The last few degrees (> 85 or < -85 degrees) +are not part of a Mercator map at all because they would be stretched too much +and the rows close to the edge will show banding, because they originate from +the same row in the original map.</p> + +<p>To overcome this, the program will by default do interpolation of pixel +colors, which will eliminate the banding effect, but will cause some blurring +of the output. With the -nomix option, this interpolation of colors isn't +applied. You can obtain the highest quality output by starting with an input +map of high resolution, so that you can follow the <b>pnmmercator</b> +transformation with a <b>pamscale</b> reduction in size.</p> + +<p>This program can also convert a Mercator projection map back to a +rectangular projection based. As said, the Mercator map doesn't have +information about the latitudes close to the poles. Therefore the top rows in +the output image will be identical and copied from the row corresponding with +latitude of 85 degrees. The same at the bottom of the map.</p> + +<p>Pnmmercator doesn't have any provision for scaling the image. You can scale +by piping the output of the program through Netpbm programs such as +<b>pamscale</b>.</p> + +<p>You can find maps to be used as input at <a +href="http://flatplanet.sourceforge.net/maps/natural.html">flatplanet.sourceforge.net</a> +or <a href="http://www.evl.uic.edu/pape/data/Earth/">uic.edu/pape</a>.</p> + +<p>The point of a Mercator projection map is that compass directions work on +it. If you draw a straight line northeast from some point on the Mercator +map, the line traces the course you would sail if you sailed a compass bearing +of northeast from that spot. Naturally, primitive navigators appreciated +that. The biggest drawback of Mercator is that areas to the north and south +appear much larger than they are in real life. For example, Greenland appears +to be larger than South America even though it only a ninth as large. Note +that areas away from the equator are stretched north-south as well as +east-west. + +<p>A rectangular projection is one where vertical distance is proportional to +angular latitude distance of the represented area and horizontal distance is +proportional to angular longitude. + + +<h2 id="parameters">PARAMETERS</h2> + +<p><b><i>filename</i></b> is the name of the input file. If you don't specify +this, <b>pnmmercator</b> reads the image from standard Input.</p> + +<h2 id="options">OPTIONS</h2> +<dl compact="compact"> +<dt><b>-inverse</b></dt> +<dd> +<p>With this option a conversion from Mercator to degrees is applied.The +output image will have half the height of the input map.</p> +</dd> +<dt><b>-nomix</b></dt> +<dd> +<p>Default behaviour is that color blending is applied in between two adjacent +rows. If you specify the -nomix parameter there is no blending. The +consequence is a banding at the top and bottom of the map. With this option, +the output map will also consist of exactly the same colors as the input.</p> +</dd> +<dt><b>-verbose</b> and <b>-vverbose</b></dt> +<dd> +<p>This parameter outputs some additional information. If you double the 'v', +it will output debug data about the lat/long degree and Mercator +conversions.</p> +</dd> +</dl> + +<h2 id="seealso">SEE ALSO</h2> +<b><a href="http://netpbm.sourceforge.net/doc/pnm.html">pnm</a></b> and +<b><a href="http://netpbm.sourceforge.net/doc/pamscale.html">pamscale</a></b> +<b><a href="http://netpbm.sourceforge.net/doc/ppmglobe.html">ppmglobe</a></b> + +<h2 id="history">HISTORY</h2> +<p><b>pnmmercator</b> was new in Netpbm 10.49 (December 2009).</p> + +<h2 id="authors">AUTHORS</h2> + +<p><a href="mailto:willem@schaik.com">Willem van Schaik</a> (of +<b>pnmtopng</b>/<b>pngtopnm</b> fame) wrote this program in October 2009 and +suggested it for inclusion in Netpbm.</p> + +<hr> + +<h2 id="index">Table Of Contents</h2> +<ul> +<li><a href="#synopsis">SYNOPSIS</a> +</li><li><a href="#description">DESCRIPTION</a> +</li><li><a href="#parameters">PARAMETERS</a> +</li><li><a href="#options">OPTIONS</a> +</li><li><a href="#seealso">SEE ALSO</a> +</li><li><a href="#authors">AUTHORS</a> +</li> +</ul> +</body> +</html> + |