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<p>Celestial transformation parameters.
<a href="structcelprm.html#details">More...</a></p>
<p><code>#include <<a class="el" href="cel_8h_source.html">cel.h</a>></code></p>
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Data Fields</h2></td></tr>
<tr class="memitem:a408a39c1d060d5b32f884f8a8c60aaa2"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a408a39c1d060d5b32f884f8a8c60aaa2">flag</a></td></tr>
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<tr class="memitem:a74585275b64c292b394b74f2f19a8048"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a74585275b64c292b394b74f2f19a8048">offset</a></td></tr>
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<tr class="memitem:ab034f85dc785113c396c9864cdddfe52"><td class="memItemLeft" align="right" valign="top">double </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#ab034f85dc785113c396c9864cdddfe52">phi0</a></td></tr>
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<tr class="memitem:a011e38b3a5505fdc13855348571bfad1"><td class="memItemLeft" align="right" valign="top">double </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a011e38b3a5505fdc13855348571bfad1">theta0</a></td></tr>
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<tr class="memitem:a3f9ae993e97f0e73e3f59117929eeda6"><td class="memItemLeft" align="right" valign="top">double </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a3f9ae993e97f0e73e3f59117929eeda6">ref</a> [4]</td></tr>
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<tr class="memitem:abe1991f17c0ecb857d5bd30a6a689b84"><td class="memItemLeft" align="right" valign="top">struct <a class="el" href="structprjprm.html">prjprm</a> </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#abe1991f17c0ecb857d5bd30a6a689b84">prj</a></td></tr>
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<tr class="memitem:a80ea2023638ededd2760cc9a260c456b"><td class="memItemLeft" align="right" valign="top">double </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a80ea2023638ededd2760cc9a260c456b">euler</a> [5]</td></tr>
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<tr class="memitem:a756c8f0991a748ab47361b0215c4577b"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a756c8f0991a748ab47361b0215c4577b">latpreq</a></td></tr>
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<tr class="memitem:a7bb5e1ff4d73c884d73eeb0f8f2677d7"><td class="memItemLeft" align="right" valign="top">int </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a7bb5e1ff4d73c884d73eeb0f8f2677d7">isolat</a></td></tr>
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<tr class="memitem:a1b9cbfd7cfa2306464d57dc4acd03b06"><td class="memItemLeft" align="right" valign="top">struct <a class="el" href="structwcserr.html">wcserr</a> * </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#a1b9cbfd7cfa2306464d57dc4acd03b06">err</a></td></tr>
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<tr class="memitem:acab5a98c001b85a565b7976499c1739c"><td class="memItemLeft" align="right" valign="top">void * </td><td class="memItemRight" valign="bottom"><a class="el" href="structcelprm.html#acab5a98c001b85a565b7976499c1739c">padding</a></td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p>The <b>celprm</b> struct contains information required to transform celestial coordinates. It consists of certain members that must be set by the user (<em>given</em>) and others that are set by the WCSLIB routines (<em>returned</em>). Some of the latter are supplied for informational purposes and others are for internal use only.</p>
<p>Returned <b>celprm</b> struct members must not be modified by the user. </p>
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<p>(Given and returned) This flag must be set to zero whenever any of the following <b>celprm</b> struct members are set or changed:</p>
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<a class="el" href="structcelprm.html#a74585275b64c292b394b74f2f19a8048">celprm::offset</a>, </li>
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<a class="el" href="structcelprm.html#ab034f85dc785113c396c9864cdddfe52">celprm::phi0</a>, </li>
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<a class="el" href="structcelprm.html#a011e38b3a5505fdc13855348571bfad1">celprm::theta0</a>, </li>
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<a class="el" href="structcelprm.html#a3f9ae993e97f0e73e3f59117929eeda6">celprm::ref</a>[4], </li>
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<a class="el" href="structcelprm.html#abe1991f17c0ecb857d5bd30a6a689b84">celprm::prj</a>: <ul>
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<a class="el" href="structprjprm.html#a4f3c364f16d0b6498d7e11e6bb67239c">prjprm::code</a>, </li>
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<a class="el" href="structprjprm.html#a3894c2e551929b29adce50cd637fa351">prjprm::r0</a>, </li>
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<a class="el" href="structprjprm.html#a46d6928a9026e7b3376dcf0d3f91db64">prjprm::pv</a>[], </li>
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<a class="el" href="structprjprm.html#a699ad609ff7c1935d8fb6a457a5b8164">prjprm::phi0</a>, </li>
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<a class="el" href="structprjprm.html#ae91fa3ff034b1c6de3ec98d8fb9e0ab1">prjprm::theta0</a>. </li>
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<p>This signals the initialization routine, <a class="el" href="cel_8h.html#ab0f67d1727750616f71c7bfcb3a037b6" title="Setup routine for the celprm struct. ">celset()</a>, to recompute the returned members of the <b>celprm</b> struct. <a class="el" href="cel_8h.html#ab0f67d1727750616f71c7bfcb3a037b6" title="Setup routine for the celprm struct. ">celset()</a> will reset flag to indicate that this has been done. </p>
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<p>(<em>Given</em>) If true (non-zero), an offset will be applied to <img class="formulaInl" alt="$(x,y)$" src="form_0.png"/> to force <img class="formulaInl" alt="$(x,y)$" src="form_0.png"/> = (0,0) at the fiducial point, ( <img class="formulaInl" alt="$\phi_0$" src="form_3.png"/>, <img class="formulaInl" alt="$\theta_0$" src="form_4.png"/>). Default is 0 (false). </p>
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<p>(<em>Given</em>) The native longitude, <img class="formulaInl" alt="$\phi_0$" src="form_3.png"/> [deg], and ... </p>
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<p>(<em>Given</em>) ... the native latitude, <img class="formulaInl" alt="$\theta_0$" src="form_4.png"/> [deg], of the fiducial point, i.e. the point whose celestial coordinates are given in <a class="el" href="structcelprm.html#a3f9ae993e97f0e73e3f59117929eeda6">celprm::ref</a>[1:2]. If undefined (set to a magic value by <a class="el" href="prj_8h.html#ad994cb23871c51b20754973bef180f8a" title="Default constructor for the prjprm struct. ">prjini()</a>) the initialization routine, <a class="el" href="cel_8h.html#ab0f67d1727750616f71c7bfcb3a037b6" title="Setup routine for the celprm struct. ">celset()</a>, will set this to a projection-specific default. </p>
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<p>(<em>Given</em>) The first pair of values should be set to the celestial longitude and latitude of the fiducial point [deg] - typically right ascension and declination. These are given by the <code><b>CRVAL</b>ia</code> keywords in FITS.</p>
<p>(Given and returned) The second pair of values are the native longitude, <img class="formulaInl" alt="$\phi_{\mathrm p}$" src="form_5.png"/> [deg], and latitude, <img class="formulaInl" alt="$\theta_{\mathrm p}$" src="form_6.png"/> [deg], of the celestial pole (the latter is the same as the celestial latitude of the native pole, <img class="formulaInl" alt="$\delta_{\mathrm p}$" src="form_7.png"/>) and these are given by the FITS keywords <code><b>LONPOLE</b>a</code> and <code><b>LATPOLE</b>a</code> (or by <code><b>PV</b>i<b>_2</b>a</code> and <code><b>PV</b>i<b>_3</b>a</code> attached to the longitude axis which take precedence if defined).</p>
<p><code><b>LONPOLE</b>a</code> defaults to <img class="formulaInl" alt="$\phi_0$" src="form_3.png"/> (see above) if the celestial latitude of the fiducial point of the projection is greater than or equal to the native latitude, otherwise <img class="formulaInl" alt="$\phi_0$" src="form_3.png"/> + 180 [deg]. (This is the condition for the celestial latitude to increase in the same direction as the native latitude at the fiducial point.) ref[2] may be set to <b><code>UNDEFINED</code></b> (from <a class="el" href="wcsmath_8h.html">wcsmath.h</a>) or 999.0 to indicate that the correct default should be substituted.</p>
<p><img class="formulaInl" alt="$\theta_{\mathrm p}$" src="form_6.png"/>, the native latitude of the celestial pole (or equally the celestial latitude of the native pole, <img class="formulaInl" alt="$\delta_{\mathrm p}$" src="form_7.png"/>) is often determined uniquely by <code><b>CRVAL</b>ia</code> and <code><b>LONPOLE</b>a</code> in which case <code><b>LATPOLE</b>a</code> is ignored. However, in some circumstances there are two valid solutions for <img class="formulaInl" alt="$\theta_{\mathrm p}$" src="form_6.png"/> and <code><b>LATPOLE</b>a</code> is used to choose between them. <code><b>LATPOLE</b>a</code> is set in ref[3] and the solution closest to this value is used to reset ref[3]. It is therefore legitimate, for example, to set ref[3] to +90.0 to choose the more northerly solution - the default if the <code><b>LATPOLE</b>a</code> keyword is omitted from the FITS header. For the special case where the fiducial point of the projection is at native latitude zero, its celestial latitude is zero, and <code><b>LONPOLE</b>a</code> = <img class="formulaInl" alt="$\pm$" src="form_8.png"/> 90.0 then the celestial latitude of the native pole is not determined by the first three reference values and <code><b>LATPOLE</b>a</code> specifies it completely.</p>
<p>The returned value, <a class="el" href="structcelprm.html#a756c8f0991a748ab47361b0215c4577b">celprm::latpreq</a>, specifies how <code><b>LATPOLE</b>a</code> was actually used. </p>
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<p>(Given and returned) Projection parameters described in the prologue to <a class="el" href="prj_8h.html">prj.h</a>. </p>
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<p>(<em>Returned</em>) Euler angles and associated intermediaries derived from the coordinate reference values. The first three values are the <img class="formulaInl" alt="$Z$" src="form_9.png"/>-, <img class="formulaInl" alt="$X$" src="form_10.png"/>-, and <img class="formulaInl" alt="$Z'$" src="form_11.png"/>-Euler angles [deg], and the remaining two are the cosine and sine of the <img class="formulaInl" alt="$X$" src="form_10.png"/>-Euler angle. </p>
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<p>(<em>Returned</em>) For informational purposes, this indicates how the <code><b>LATPOLE</b>a</code> keyword was used </p>
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0: Not required, <img class="formulaInl" alt="$\theta_{\mathrm p}$" src="form_6.png"/> (== <img class="formulaInl" alt="$\delta_{\mathrm p}$" src="form_7.png"/>) was determined uniquely by the <code><b>CRVAL</b>ia</code> and <code><b>LONPOLE</b>a</code> keywords. </li>
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1: Required to select between two valid solutions of <img class="formulaInl" alt="$\theta_{\mathrm p}$" src="form_6.png"/>. </li>
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2: <img class="formulaInl" alt="$\theta_{\mathrm p}$" src="form_6.png"/> was specified solely by <code><b>LATPOLE</b>a</code>. </li>
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<p>(<em>Returned</em>) True if the spherical rotation preserves the magnitude of the latitude, which occurs iff the axes of the native and celestial coordinates are coincident. It signals an opportunity to cache intermediate calculations common to all elements in a vector computation. </p>
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<p>(<em>Returned</em>) If enabled, when an error status is returned this struct contains detailed information about the error, see <a class="el" href="wcserr_8h.html#a1691b8bd184d40ca6fda255be078fa53" title="Enable/disable error messaging. ">wcserr_enable()</a>. </p>
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<p>(An unused variable inserted for alignment purposes only.)</p>
<p>Global variable: const char *cel_errmsg[] - Status return messages Status messages to match the status value returned from each function. </p>
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