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diff --git a/pkg/images/imcoords/doc/hpctran.hlp b/pkg/images/imcoords/doc/hpctran.hlp new file mode 100644 index 00000000..16a550c3 --- /dev/null +++ b/pkg/images/imcoords/doc/hpctran.hlp @@ -0,0 +1,109 @@ +.help hpctran Jul09 imcoords +.ih +NAME +hpctran -- Convert between HEALPix row and spherical coordinate +.ih +USAGE +hpctran lng=xxx lat=xxx +.br +hpctran row=xxx +.ih +PARAMETERS +.ls row +HEALPix table row (1 indexed). +This is used as input if the direction +is "row2ang" or is used to store the value if the direction is +"ang2row". +.le +.ls lng, lat +Spherical coordinate consisting of a longitude and latitude. +These are used as input if the direction +is "ang2row" or is used to store the value if the direction is +"row2ang". The units are interpreted as selected by the \fIcunits\fR +parameter. The type of coordinates appropriate for a particular map +is defined by the map provider. +.le +.ls nside = 512 +The number of pixels per face side. +.le +.ls cunits = "degrees" (degrees|hourdegree|radians) +The units of the longitude and latitude. The "hourdegree" is for +longitude in hours and latitude in degrees. +.le +.ls maptype = "nest" (nest|ring) +The map pixelization type which may be "nest" or "ring". +.le +.ls direction = "ang2row" (ang2row|row2ang) +The conversion direction. "ang2row" converts a spherical coordinate +to a map row or pixel number. "row2ang" converts a map row or pixel +number to a spherical coordinate. +.le +.ih +DESCRIPTION +HEALPix is an acronym for Hierarchical Equal Area isoLatitude Pixelization +of a sphere. See the reference section for a technical description of the +pixelization and mathematics. As suggested in the name, this pixelization, +or tiling, produces a subdivision of a spherical surface in which each +"pixel" covers the same surface area as every other pixel. A HEALPix FITS +"map" is a table where each row contains "pixel" data for a region on the +sphere. It is a table because the pixels don't form a raster as in an +image. + +The pixelization is defined by a resolution parameter which may be expressed +in various ways. This task uses the number of pixels along a side of one of +the 12 basic faces. The number of pixels/rows is 12 * nside * nside. The +pixelization has two forms supported by this task. These are called +"nested" and "ring". + +The HEALPix WCS task, \fBhpctran\fR, provides a translation between +the table row number and a spherical coordinate. It is up to the +creator of the table to choose the spherical coordinate system. This +might be an equatorial, galactic, or super-galactic system. There may +be a keyword specifying the system. This is the case with WMAP data. + +This task only provides the conversion. Access to the "pixel" data +requires other tools. For binary tables the \fBtables\fR may be used. + +This task allows the spherical coordinates to be input and output in three +forms, as hours and degrees (e.g. RA/DEC), as degrees (e.g. l/b), and as +radians. On input one may use sexagesimal since IRAF automatically converts +this to decimal. On output the values are produced in decimal form. + +The output is provide in two ways to provide flexibility in scripting. One +is writing the results to the task parameters. Note that it is recommended +that tasks which write to there parameter be "cached" with the \fBcache\fR +command to avoid problems with background submission or multiple scripts +running in parallel. The other output is printed to the standard output. +Regardless of the direction of conversion the printed output is in the same +order of row number, longitude, and latitude. + +.ih +EXAMPLES +A CMB WMAP file is obtained and one wants the temperature at a particular +point on the sky. Note that the WMAP format is "nested" and +coordinate system is galactic. + +.nf +cl> hpctran lng=50.12 lat=-33.45 +2298092 50.12 -33.45000000000001 +cl> = hpctran.row +2298092 +cl> tdump wmap_iqusmap_r9_5yr_K1_v3.fits col=TEMPERATURE row=2298092 +cl> tdump ("wmap_iqusmap_r9_5yr_K1_v3.fits", col="TEMPERATURE", +>>> row=hpctran.row) +.fi + +.ih +REFERENCE +\fIHEALPIX - a Framework for High Resolution Discretization, and Fast +Analysis of Data Distributed on the Sphere\fR, +by K.M. Gorski, Eric Hivon, A.J. Banday, B.D. Wandelt, F.K. Hansen, M. +Reinecke, M. Bartelmann, 2005, ApJ 622, 759. +.ih +CREDIT +Some code from the HEALPix distribution at http://healpix.jpl.nasa.gov +was translated to SPP for use in this routine. +.ih +SEE ALSO +ttools +.endhelp |