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diff --git a/noao/onedspec/doc/sflip.hlp b/noao/onedspec/doc/sflip.hlp new file mode 100644 index 00000000..66790e4e --- /dev/null +++ b/noao/onedspec/doc/sflip.hlp @@ -0,0 +1,114 @@ +.help sflip Jul94 noao.onedspec +.ih +NAME +sflip -- Flip data and/or dispersion coordinates in spectra +.ih +USAGE +sflip input output +.ih +PARAMETERS +.ls input +List of input images containing spectra to be flipped. +.le +.ls output +Matching list of output image names for flipped spectra. +If no list is specified then the flipped spectra will replace the input +spectra. If the output image name matching an input image name is the +same then the flipped spectrum will replace the original spectrum. +.le +.ls coord_flip = no +Flip the dispersion coordinates? If yes then the relationship between the +logical pixel coordinates and the dispersion coordinates will be reversed so +that the dispersion coordinate of the first pixel of the output image will +correspond to the coordinate of the last pixel in the input image and +vice-versa for the other endpoint pixel. The physical coordinates +will also be flipped. Only the coordinate system along the dispersion +axis is flipped. +.le +.ls data_flip = yes +Flip the order of the data pixels as they are stored in the image along +the dispersion axis? If yes then the first pixel in the input spectrum +becomes the last pixel in the output spectrum along the dispersion +axis of the image. +.le +.ih +DESCRIPTION +The dispersion coordinate system and/or the data in the spectra specified +by the input list of images are flipped and stored in the matching output +image given in the output list of images. If the output image list is left +blank or an output image name is the same as an input image name then the +operation is done so that the flipped spectra in the image replace the +original spectra. All of the supported spectrum types are allowed; one +dimensional images, collections of spectra in multispec format, and two and +three dimensional spatial spectra in which one axis is dispersion. In all +cases the flipping affects only the dispersion axis of the image as +specified by the DISPAXIS header keyword or the "dispaxis" parameter. The +parameters \fIcoord_flip\fR and \fIdata_flip\fR select whether the +coordinate system and data are flipped. If neither operation is selected +then the output spectra will simply be copies of the input spectra. + +Flipping of the coordinate system means that the relation between +"logical" pixel coordinates (the index system of the image array) +and the dispersion and physical coordinate systems is reversed. +The dispersion coordinate of the first pixel in the flipped spectrum +will be the same as the dispersion coordinate of the last pixel +in the original spectrum and vice-versa for the other endpoint. + +Flipping of the data means that the order in which the pixels are stored +in the image file is reversed along the image axis corresponding to +the dispersion. + +While flipping spectra seems simple there are some subtleties. If +both the coordinate system and the data are flipped then plots of +the spectra in which the dispersion coordinates are shown will appear +the same as in the original spectra. In particular the coordinate +of a feature in the spectrum will remain unchanged. In contrast +flipping either the coordinate system or the data will cause features +in the spectrum to move to opposite ends of the spectrum relative +to the dispersion coordinates. + +Since plotting programs often plot the dispersion axis in some standard way +such as increasing from left to right, flipping both the dispersion +coordinates and the data will produce plots that look identical even though +the order of the points plotted will be reversed. Only if the spectra are +plotted against logical pixel coordinates will a change be evident. Note +also that the plotting programs themselves have options to reverse the +displayed graph. So if all one wants is to reverse the direction of +increasing dispersion in a plot then physically flipping of the spectra is +not generally necessary. + +Flipping of both the coordinate system and the data is also equivalent +to using an image section with a reversed axis. For example +a one dimensional spectrum can be flipped in both dispersion coordinates +and data pixel order by + +.nf + cl> imcopy spec1[-*] spec2 +.fi + +Higher dimensional spectra need appropriate dimensions in the image +sections. One advantage of \fBsflip\fR is that it will determine the +appropriate dispersion axis itself. +.ih +EXAMPLES +In the following the spectra can be one dimensional, multispec, +long slit, or spectral data cubes. + +.nf + cl> sflip spec1 spec1f # Flip data to new image + cl> sflip spec1 spec1 # Flip data to same image + cl> sflip spec1 spec1f coord+ data- # Flip coordinates and not data + cl> sflip spec1 spec1f coord+ # Flip both coordinates and data + cl> sflip spec* f//spec* # Flip a list of images +.fi +.ih +REVISIONS +.ls SFLIP V2.10.4 +New in this release. Note that the V2.9 SFLIP was different in that +it was script which simply flipped the data. Coordinate systems were +not handled in the same way. +.le +.ih +SEE ALSO +imcopy, scopy, dispcor, sapertures +.endhelp |