1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<!--Converted with LaTeX2HTML 99.2beta8 (1.46)
original version by: Nikos Drakos, CBLU, University of Leeds
* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
* with significant contributions from:
Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
<HTML>
<HEAD>
<TITLE>5.2.1 Albers Conic Equal-Area Projection (-Jb -JB)</TITLE>
<META NAME="description" CONTENT="5.2.1 Albers Conic Equal-Area Projection (-Jb -JB)">
<META NAME="keywords" CONTENT="GMT_Docs">
<META NAME="resource-type" CONTENT="document">
<META NAME="distribution" CONTENT="global">
<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1">
<META NAME="Generator" CONTENT="LaTeX2HTML v99.2beta8">
<META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css">
<LINK REL="STYLESHEET" HREF="GMT_Docs.css">
<LINK REL="next" HREF="node43.html">
<LINK REL="previous" HREF="node41.html">
<LINK REL="up" HREF="node41.html">
<LINK REL="next" HREF="node43.html">
</HEAD>
<BODY bgcolor="#ffffff">
<!--Navigation Panel-->
<A NAME="tex2html1582"
HREF="node43.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.gif"></A>
<A NAME="tex2html1576"
HREF="node41.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.gif"></A>
<A NAME="tex2html1570"
HREF="node41.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.gif"></A>
<A NAME="tex2html1578"
HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.gif"></A>
<A NAME="tex2html1580"
HREF="node149.html">
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.gif"></A>
<BR>
<B> Next:</B> <A NAME="tex2html1583"
HREF="node43.html">5.2.2 Lambert Conic Conformal</A>
<B> Up:</B> <A NAME="tex2html1577"
HREF="node41.html">5.2 Conic Projections</A>
<B> Previous:</B> <A NAME="tex2html1571"
HREF="node41.html">5.2 Conic Projections</A>
  <B> <A NAME="tex2html1579"
HREF="node1.html">Contents</A></B>
  <B> <A NAME="tex2html1581"
HREF="node149.html">Index</A></B>
<BR>
<BR>
<!--End of Navigation Panel-->
<H2><A NAME="SECTION001321000000000000000">
5.2.1 Albers Conic Equal-Area Projection (<B>-Jb</B> <B>-JB</B>)</A>
</H2>
<A NAME="6351"></A>
<A NAME="6352"></A>
<A NAME="6353"></A>
<P>
This projection, developed by Albers in 1805, is predominantly
used to map regions of large east-west extent, in particular
the United States. It is a conic, equal-area projection, in
which parallels are unequally spaced arcs of concentric circles,
more closely spaced at the north and south edges of the map.
Meridians, on the other hand, are equally spaced radii about
a common center, and cut the parallels at right angles.
Distortion in scale and shape vanishes along the two standard
parallels. Between them, the scale along parallels is too small;
beyond them it is too large. The opposite is true for the scale
along meridians. To define the projection in <A NAME="tex2html305"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> you need to
provide the following information:
<P>
<DL>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Longitude and latitude of the projection center
</DD>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Two standard parallels
</DD>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Map scale in inch/degree or 1:xxxxx notation (<B>-Jb</B>),
or map width (<B>-JB</B>)
<P>
</DD>
</DL>
<P>
Note that you must include the ``1:'' if you choose to specify the
scale that way. E.g., you can say 0.5 which means 0.5 inch/degree
or 1:200000 which means 1 inch on the map equals 200,000 inches
along the standard parallels. The projection center defines the
origin of the rectangular map coordinates. As an example we will
make a map of the region near Taiwan. We choose the center of
the projection to be at 125 <IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">E/20 <IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N and 25 <IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N
and 45 <IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N as our two standard parallels. We desire a map
that is 5 inches wide. The complete command needed to generate
the map below is therefore given by:
<P>
<P>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<BR>
<PRE>
#!/bin/sh
# $Id: GMT_albers.sh,v 1.1 2001/03/21 04:10:21 pwessel Exp $
#
gmtset GRID_CROSS_SIZE 0
pscoast -R110/140/20/35 -JB125/20/25/45/5i -B10g5 -Dl -G200 -W0.25p -A250 -P > GMT_albers.ps
</PRE>
<P>
<BR>
<BR>
<P>
<BR CLEAR="ALL">
<HR>
<P>
<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_albers"></A><A NAME="6454"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.6:</STRONG>
Albers equal-area conic map projection</CAPTION>
<TR><TD><IMG
WIDTH="680" HEIGHT="380" BORDER="0"
SRC="img68.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_albers.eps}\end{figure}"></TD></TR>
</TABLE>
</DIV><P></P>
<P>
<A NAME="6445"></A>
<A NAME="6446"></A>
<A NAME="6447"></A>
<P>
<HR>
<!--Navigation Panel-->
<A NAME="tex2html1582"
HREF="node43.html">
<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next.gif"></A>
<A NAME="tex2html1576"
HREF="node41.html">
<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up.gif"></A>
<A NAME="tex2html1570"
HREF="node41.html">
<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="prev.gif"></A>
<A NAME="tex2html1578"
HREF="node1.html">
<IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="contents.gif"></A>
<A NAME="tex2html1580"
HREF="node149.html">
<IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="index.gif"></A>
<BR>
<B> Next:</B> <A NAME="tex2html1583"
HREF="node43.html">5.2.2 Lambert Conic Conformal</A>
<B> Up:</B> <A NAME="tex2html1577"
HREF="node41.html">5.2 Conic Projections</A>
<B> Previous:</B> <A NAME="tex2html1571"
HREF="node41.html">5.2 Conic Projections</A>
  <B> <A NAME="tex2html1579"
HREF="node1.html">Contents</A></B>
  <B> <A NAME="tex2html1581"
HREF="node149.html">Index</A></B>
<!--End of Navigation Panel-->
<ADDRESS>
Paul Wessel
2001-04-18
</ADDRESS>
</BODY>
</HTML>
|
