diff options
Diffstat (limited to 'noao/imred/echelle/doc/ecidentify.hlp')
| -rw-r--r-- | noao/imred/echelle/doc/ecidentify.hlp | 770 |
1 files changed, 770 insertions, 0 deletions
diff --git a/noao/imred/echelle/doc/ecidentify.hlp b/noao/imred/echelle/doc/ecidentify.hlp new file mode 100644 index 00000000..61187a43 --- /dev/null +++ b/noao/imred/echelle/doc/ecidentify.hlp @@ -0,0 +1,770 @@ +.help ecidentify May88 noao.imred.echelle +.ih +NAME +ecidentify -- Determine the dispersion relation in echelle spectra +.ih +USAGE +ecidentify images +.ih +PARAMETERS +.ls images +List of echelle format spectra in which to identify lines and fit +dispersion functions. +.le +.ls database = "database" +Database in which the feature data and dispersion functions are recorded. +.le +.ls coordlist = "linelists$idhenear.dat" +User coordinate list consisting of an ordered list of line coordinates. A +comment line of the form "# units <units>", where <units> is one of the +understood units names, defines the units of the line list. If no units +are specified then Angstroms are assumed. Some standard line lists are +available in the directory "linelists$". The standard line lists are +described under the topic \fIlinelists\fR. +.le +.ls units = "" +The units to use if no database entry exists. The units are specified as +described in + +.nf + cl> help onedspec.package section=units +.fi + +If no units are specified and a coordinate list is used then the units of +the coordinate list are selected. If a database entry exists then the +units defined there override both this parameter and the coordinate list. +.le +.ls match = 1. +The maximum difference for a match between the feature coordinate function +value and a coordinate in the coordinate list. The unit of this parameter +is that of the user coordinates. +.le +.ls maxfeatures = 100 +Maximum number of the strongest features to be selected automatically from +the coordinate list (function 'l') or from the image data (function 'y'). +.le +.ls zwidth = 10. +Width of graphs, in user coordinates, when in zoom mode (function 'z'). +.le + +The following parameters are used in determining feature positions. +.ls ftype = "emission" +Type of features to be identified. The possibly abbreviated choices are +"emission" and "absorption". +.le +.ls fwidth = 4. +Width in pixels of features to be identified. +.le +.ls cradius = 5. +The maximum distance, in pixels, allowed between a feature position +and the initial estimate when defining a new feature. +.le +.ls threshold = 10. +In order for a feature center to be determined the range of pixel intensities +around the feature must exceed this threshold. +.le +.ls minsep = 2. +The minimum separation, in pixels, allowed between feature positions +when defining a new feature. +.le + +The following default parameters are used when fitting a function to +the user coordinates. If a previous solution is read from the database +then the parameters from that solution override the defaults below. +.ls function = "chebyshev" +The function to be fit to the user coordinates as a function of the pixel +coordinate and aperture number. The choices are bi-dimensional +"chebyshev" and "legendre" polynomials. +.le +.ls xorder = 2 +Order of the fitting function along each echelle order. +The order is the number of polynomial terms; i.e. xorder = 2 is a linear +function. +.le +.ls yorder = 2 +Order of the fitting function with respect to the aperture number. +The order is the number of polynomial terms; i.e. yorder = 2 is a linear +function. +.le +.ls niterate = 0, lowreject = 3, highreject = 3. +Default number of rejection iterations and the sigma clipping thresholds. If +\fIniterate\fR is zero then no rejection is done. +.le + +The following parameters control the graphics input and output. +.ls graphics = "stdgraph" +Graphics device. The default is the standard graphics device which is +generally a graphics terminal. +.le +.ls curosr = "" +Cursor input file. If a cursor file is not given then the standard graphics +cursor is read. +.le +.ih +CURSOR KEYS + +.nf + ECIDENTIFY CURSOR KEY AND COLON COMMAND SUMMARY + +? Help a Affect all features c Center feature(s) +d Delete feature(s) f Fit dispersion g Fit zero point shift +i Initialize j Go to previous order k Go to next order +l Match coordinate list m Mark feature n Next feature +o Go to specified order p Pan graph q Quit +r Redraw graph s Shift feature t Reset position +u Enter user coordinate w Window graph x Crosscorrelate peaks +y Find peaks z Zoom graph . Nearest feature ++ Next feature - Previous feature I Interrupt + +:show [file] :features [file] :coordlist [file] +:cradius [value] :threshold [value] :database [file] +:ftype [type] :fwidth [value] :image [image] +:labels [type] :match [value] :maxfeatures [value] +:minsep [value] :read [image] :write [image] +:zwidth [value] + + + ECHELLE DISPERSION FUNCTION FITTING COMMAND SUMMARY + +? Help c Print coordinates d Delete point +f Fit dispersion o Fit with fixed order offset q Quit +r Redraw graph u Undelete point w Window graph +x Set ordinate y Set abscissa I Interrupt + +:show :function [value] :highreject [value] :lowreject [value] +:niterate [value] :xorder [value] :yorder [value] + +.fi + + ECIDENTIFY CURSOR KEYS AND COLON COMMANDS +.ls ? +Clear the screen and print a menu of cursor and colon commands. +.le +.ls a +Apply next (c)enter or (d)elete operation to (a)ll features +.le +.ls c +(C)enter the feature nearest the cursor. Used when changing the position +finding parameters or when features are defined from a previous feature list. +May be used in combination with the (a)ll key. +.le +.ls d +(D)elete the feature nearest the cursor. (D)elete all features when preceded +by the (a)ll key. This does not affect the dispersion function. +.le +.ls f +(F)it a function of the pixel coordinates and aperture numbers to the user +coordinates. This enters an interactive function fitting package. +.le +.ls g +Fit a zero point shift to the user coordinates by minimizing the difference +between the user and fitted coordinates. The coordinate dispersion function +is not changed. +.le +.ls i +(I)nitialize (delete features and dispersion function fit). +.le +.ls j +Go to the next aperture in decreasing line number in the echelle format image. +Wrap around to the last line from the first line. +.le +.ls k +Go to the next aperture in increasing line number in the echelle format image. +Wrap around to the first line from the last line. +.le +.ls l +(L)ocate features in the coordinate list. A coordinate function must be +defined or at least four features in more than one aperture must have user +coordinates from which a coordinate function can be determined by an +initial automatic function fit. +.le +.ls m +(M)ark a new feature using the cursor position as the initial position +estimate. +.le +.ls n +Move the cursor or zoom to the (n)ext feature (same as +). +.le +.ls o +Go to a specific aperture (related to an echelle (o)rder). The user +is queried for the aperture number. +.le +.ls p +(P)an to the original window after (z)ooming on a feature. +.le +.ls q +(Q)uit and continue with next image. +.le +.ls r +(R)edraw the graph. +.le +.ls s +(S)hift the fit coordinates relative to the pixel coordinates. The +user specifies the desired coordinate at the position of the cursor +and a zero point shift to the fit coordinates is applied. If features +are defined then they are recentered and the shift is the average shift. +The shift in pixels, user coordinates, and z (fractional shift) is printed. +The user shift is for the fundamental order and the shift for each order +is then given by this shift divided by the order number. +.le +.ls t +Reset the current feature to the position of the cursor. The feature +is \fInot\fR recentered. This is used to mark an arbitrary position. +.le +.ls u +Enter a new (u)ser coordinate for the current feature. +When (m)arking a new feature the user coordinate is also requested. +.le +.ls w +(W)indow the graph. A window prompt is given and a number of windowing +options may be given. For more help type '?' to the window prompt or +see help under \fIgtools\fR. +.le +.ls x +Crosscorrelate features with the data peaks and reregister. This is +generally used with a feature list from a different image. +The mean shift in user coordinates, mean shift in pixels, and the fractional +shift in user coordinates is printed. The user shift is scaled to the +fundamental order. +.le +.ls y +Up to \fImaxfeatures\fR emission peaks are found automatically (in order of +peak intensity) and, if a dispersion solution is defined, the peaks are +identified from the coordinate list. +.le +.ls z +(Z)oom on the feature nearest the cursor. The width of the zoom window +is determined by the parameter \fIzwidth\fR. +.le +.ls . +Move the cursor or zoom window to the feature nearest the cursor. +.le +.ls 4 + +Move the cursor or zoom window to the (n)ext feature. +This does not automatically move to the next aperture. +.le +.ls 4 - +Move the cursor or zoom window to the previous feature. +This does not automatically move to the next aperture. +.le +.ls I +Interrupt the task immediately. The database is not updated. +.le + +Parameters are shown or set with the following "colon commands", which may be +abbreviated. To show the value of a parameter type the parameter name alone +and to set a new value follow the parameter name by the value. +.ls :show file +Show the values of all the parameters. If a file name is given then the +output is appended to that file. If no file is given then the terminal +is cleared and the output is sent to the terminal. +.le +.ls :features file +Print the feature list and the fit rms. If a file name is given then the +output is appended to that file. If no file is given then the terminal +is cleared and the output is sent to the terminal. +.le +.ls :coordlist file +Set or show the coordinate list file. +.le +.ls :cradius value +Set or show the centering radius in pixels. +.le +.ls :threshold value +Set or show the detection threshold for centering. +.le +.ls :database name +Set or show the database for recording feature records. +.le +.ls :ftype value +Set or show the feature type (emission or absorption). +.le +.ls :fwidth value +Set or show the feature width in pixels. +.le +.ls :image imagename +Set a new image or show the current image. +.le +.ls :labels value +Set or show the feature label type (none, index, pixel, or user). +.le +.ls :match value +Set or show the coordinate list matching distance. +.le +.ls :maxfeatures value +Set or show the maximum number of features automatically found. +.le +.ls :minsep value +Set or show the minimum separation allowed between features. +.le +.ls :read name +Read a record from the database. The record name defaults to the image name. +.le +.ls :threshold value +Set or show the centering threshold. +.le +.ls :write name +Write a record to the database. The record name defaults to the image name. +.le +.ls :zwidth value +Set or show the zoom width in user units. +.le + + + DISPERSION FUNCTION FITTING COMMANDS +.ls ? +Page help information. +.le +.ls c +Print input and fitted coordinates of point nearest the cursor. +.le +.ls d +Delete the nearest undeleted point to the cursor. +.le +.ls f +Fit a dispersion function including determining the order offset. +.le +.ls o +Fit a dispersion function with the order offset fixed. The user is queried +for the order offset. This is faster than the interactive fit to also +determine the order. +.le +.ls q +Quit and return to the spectrum display. +.le +.ls r +Redraw the graph. +.le +.ls u +Undelete the nearest deleted point to the cursor (which may be outside the +graph window). +.le +.ls w +Window the graph (type ? to the window prompt for more help). +.le +.ls x +Set the quantity plotted along the ordinate (x axis). +.le +.ls y +Set the quantity plotted along the abscissa (y axis). +.le +.ls I +Interrupt the task immediately. No information is saved in the database. +.le + +.ls :function [value] +Print or set the function type (chebyshev|legendre). +.le +.ls :show +Print current function and orders. +.le +.ls :niterate [value], :lowreject [value], :highreject [value] +Print or set the iterative rejection parameters. +.le +.ls :xorder [value] +Print or set the order for the dispersion dependence. +.le +.ls :yorder [value] +Print or set the order for the echelle order dependence. +.le +.ih +DESCRIPTION +Emission and absorption features in echelle format spectra (see \fIapsum\fR) +are identified interactively and from a line list and a dispersion +function is determined. The results of the line identifications and +dispersion function are stored in a database for further reference and +for use with the tasks \fBecreidentify\fR and \fBecdispcor\fR. Also +the reference spectrum keyword REFSPEC is added to the image header. +This is used by \fBrefspectra\fR and \fBecdispcor\fR. + +Each spectrum in the input list is identified in turn. Initially the +order in the first image line is graphed. The user may change the +displayed order with the 'j', 'k', and 'o' keys. The initial feature +list and dispersion function are read from the database if an entry +exists. The features are marked on the graph. The image coordinates +are in pixels unless a dispersion function is defined, in which case +they are in user coordinate units (usually wavelength in Angstroms). +The aperture number, pixel coordinate, coordinate function value, and +user coordinate for the current feature are displayed on the status +line. + +For consistency the orders are always identified by their aperture +numbers in this task and all other tasks. These are the +identifications assigned when extracting the orders using the task +\fIapsum\fR. If the user has assigned true order numbers as the +aperture numbers then there is no distinction between aperture and +order number. However, it is often the case that the aperture numbers +are simply assigned sequentially and the true order numbers may not +even be known. Initially the orders are the same as the apertures +numbers but after fitting a dispersion function the true order numbers +will be determined. This information is also recorded in the database +and indicated in the graph titles but selecting an order to be graphed +with 'o' and the status line information is always in terms of the +aperture number. + +The graphics cursor is used to select features and perform various +functions. A menu of the keystroke options and functions is printed +with the key '?'. The cursor keys and their functions are defined in +the CURSOR KEYS sections and described further below. The standard +cursor mode keys are also available to window and redraw the graph and +to produce hardcopy "snaps". + +There are two types of feature selection functions; defining new +features and selecting previously defined features. The key 'm' marks +a new feature nearest the cursor position. The feature position is +determined by the feature centering algorithm (see help for +\fBcenter1d\fR). The type of feature, emission or absorption, is set +by the \fIftype\fR parameter. If the new position is within a distance +given by the parameter \fIminsep\fR of a previous feature it is +considered to be the same feature and replaces the old feature +(normally the position of the new feature will be exactly the same as +the original feature). The coordinate list is searched for a match +between the coordinate function value (when defined) and a user +coordinate in the list. If a match is found it becomes the default +user coordinate which the user may override. The new feature is marked +on the graph and it becomes the current feature. The redefinition of a +feature which is within the minimum separation may be used to set the +user coordinate from the coordinate list. The key 't' allows setting +the position of a feature to other than that found by the centering +algorithm. + +The 'y' key applies a peak finding algorithm and up to the maximum +number of features (\fImaxfeatures\fR) are found. If there are more +peaks only the strongest are kept. The peaks are then matched against +the coordinate list to find user coordinate values. + +To select a different feature as the current feature the keys '.', 'n', +'+', and '-' are used. The '.' selects the feature nearest the cursor, +the 'n' and '+' select the next feature, and the '-' selects the +previous feature relative to the current feature in the feature list as +ordered by pixel coordinate. These keys are useful when redefining the +user coordinate with the 'u' key and when examining features in zoom +mode. To change apertures (orders) the 'j', 'k', and 'o' keys are +used. + +If four or more features are identified spanning the range of the data +(in pixel coordinates and in order number) or if a coordinate function +is defined then the 'l' key may be used to identify additional features +from a coordinate list. If a coordinate function is not defined the +default function is fit to the user coordinates of the currently +defined features. Then for each coordinate value in the coordinate +list the pixel coordinate is determined and a search for a feature at +that point is made. If a feature is found (based on the parameters +\fIftype, fwidth\fR, \fIcradius\fR, and \fBthreshold\fR) its user +coordinate value based on the coordinate function is determined. If +the coordinate function value matches the user coordinate from the +coordinate list within the error limit set by the parameter \fImatch\fR +then the new feature is entered in the feature list. Up to a maximum +number of features, set by the parameter \fImaxfeatures\fR, may be +defined in this way. A new user coordinate function is fit to all the +located features. Finally, the graph is redrawn in user coordinates +with the additional features found from the coordinate list marked. + +The 'f' key fits a two dimensional function of the pixel coordinates +and aperture number to the user coordinates. The type of function and +the orders are initially set with the parameters \fIfunction\fR, +\fIxorder\fR, and \fIyorder\fR. The value of the function for a +particular pixel coordinate is called the function coordinate and each +feature in the feature list has a function coordinate value. The +fitted function also is used to convert pixel coordinates to user +coordinates in the graph. Depending on the orders of the function +four or more features are required covering at least two orders. +A description of the dispersion function fitting is given the section +ECHELLE DISPERSION FUNCTION FITTING. + +If a zero point shift is desired without changing the coordinate function +the user may specify the coordinate of a point in the spectrum with +the 's' key from which a shift is determined. The 'g' key also +determines a shift by minimizing the difference between the user +coordinates and the fitted coordinates. This is used when a previously +determined coordinate function is applied to a new spectrum having +fewer or poorer lines and only a zero point shift can reasonably be +determined. Note that the zero point shift is in user coordinates +for the fundamental order. The shift for any particular order is then +the zero point shift divided by the order number. + +Features may be delete with the key 'd'. All features are deleted when +the 'a' key immediately precedes the delete key. Deleting the features +does not delete the coordinate function. To delete both the features +and the dispersion function the initialize key 'i' is used. Note +features deleted during dispersion function fitting also are removed +from the feature list upon exiting the fitting package. + +It is common to transfer the feature identifications and coordinate +function from one image to another. When a new image without a +database entry is examined, such as when going to the next image in the +input list or selecting a new image with the ":image" command, the +current feature list and coordinate function are kept. Alternatively, +a database record from a different image may be read with the ":read" +command. When transferring feature identifications between images the +feature coordinates will not agree exactly with the new image feature +positions and several options are available to reregister the feature +positions. The key 'c' centers the feature nearest the cursor using +the current position as the starting point. When preceded with the 'a' +key all the features are recentered (the user must refit the coordinate +function if desired). As an aside, the recentering function is also +useful when the parameters governing the feature centering algorithm +are changed. + +The (c)entering function is applicable when the shift between the +current and true feature positions is small. Larger shifts may be +determined automatically with the 'x' function which correlates +features in the image with the feature list. The features are then +recentered. A zero point shift may also be given interactively with +the 's' key by using the cursor to indicate the coordinate of a point +in the spectrum. If there are no features then the shift is exactly as +marked by the cursor but if there are features the approximate shift is +applied and then the features are recentered. The shift is then the +mean shift of the features after recentering. The shift is used as a +zero point offset added to the dispersion function. The shift is +computed in user coordinates for the fundamental order. Shifts for +each order are given by scaling of this shift. + +In addition to the single keystroke commands there are commands +initiated by the key ':' (colon commands). As with the keystroke +commands there are a number of standard graphics features available +begining with ":." (type ":.help" for these commands). The colon +commands allow the task parameter values to be listed and to be reset +within the task. A parameter is listed by typing its name. The colon +command ":show" lists all the parameters. A parameter value is reset +by typing the parameter name followed by the new value; for example +":match 10". Other colon commands display the feature list +(:features), control reading and writing records to the database (:read +and :write), and set the graph display format. + +The feature identification process for an image is completed by typing +'q' to quit. Attempting to quit an image without explicitly recording +changes in the feature database produces a warning message and an +opportunity to record the information in the database. As an immediate +exit the 'I' interrupt key may be used. This does not save the feature +information. +.ih +ECHELLE DISPERSION FUNCTION FITTING +If a minimum of four features over at least two orders, depending on +the default function orders, have been identified a dispersion function +relating the user coordinates to the extracted pixel coordinate and +aperture number may be fit. However, more features are preferable to +determine changes in the dispersion as a function of position and +order. + +The form of the function fit explicitly includes the basic order number +dependence of echelle spectra; namely the wavelength of a particular +point along the dispersion direction in different orders varies as the +reciprocal of the order number. Because of distortions, the differing +extraction paths through the two dimensional image, and rotations of +the spectra relative to the axis of constant dispersion (i.e. aligning +the orders with the image columns or lines instead of aligning the +emission and absorption features) there will be residual dependancies on +the extracted pixel positions and orders. These residual dependancies +are fit by a two dimensional polynomial of arbitrary order including +cross terms. Because the basic order number dependence has been +removed the orders should be relatively low. Currently the functions +are bi-dimensional chebyshev and legendre polynomials though other +function may be added in the future. + +Since the true order number may not be known initially a linear +relation between the aperture numbers and the order numbers is also +determined which minimizes the residuals. This relation allows an +unknown offset and possible a reversed direction of increasing order. +The fitted function is then represented as: + +.nf + y = offset +/- aperture + + wavelength = f (x, y) / y +.fi + +where y is the order number and x is the extracted pixel coordinate along the +dispersion. + +If the order offset is known initially or as a result of previous the 'o' +fit may be used. The dispersion minimization for the order offset is +then not done. This will, therefore, be faster than using the full +fit, key 'f', to also determine the order offset. + +The fitting is done interactively as a submode of \fBecidentify\fR with its +own set of cursor commands. It is entered using the 'f' key and exited using +the 'q' key. The list of commands is given the CURSOR KEY section and is +available from the fitting mode with '?'. The functionality of this fitting +is fairly simple; the function and orders may be changed, points may be deleted +and undeleted, and the results of the fit may be displayed in various formats +by selecting quantities to be plotted along either axis. Generally one +changes plotting of the pixel coordinate, order number, and wavelength +along the x axis and residuals or radial velocity errors along the y axis. +One switches between increasing the x order and the y order while switching +between plotting verses x positions and order number until the residuals +have been reduced to remove all systematic trends. +.ih +DATABASE RECORDS +The database specified by the parameter \fIdatabase\fR is a directory of +simple text files. The text files have names beginning with 'ec' followed +by the entry name, usually the name of the image. The database text files +consist of a number of records. A record begins with a line starting with the +keyword "begin". The rest of the line is the record identifier. Records +read and written by \fBecidentify\fR have "ecidentify" as the first word of the +identifier. Following this is a name which may be specified following the +":read" or ":write" commands. If no name is specified then the image name +is used. The lines following the record identifier contain +the feature information and dispersion function coefficients. +.ih +ECHELLE DISPERSION FUNCTIONS +The fitted echelle dispersion functions are evaluated as described in +this section. The basic equations are + +.nf + (1) w = (f(x,o) + shift) / o + (2) o = ap * slope + offset +.fi + +where w is the wavelength, x is the pixel coordinate along the order, o is +the order, and ap is the aperture number. The database parameter "shift" +provides a wavelength zero point shift and the parameters "slope" and +"offset" provide the transformation between aperture number and order. +Note that the function f(x,o) and the shift are in terms of first order +wavelengths. + +The database entries contain "parameter value" pairs. This includes the +parameters "shift", "offset", and "slope" defined above. The default +values for these if they are absent are 0, 0, and 1 respectively. The +"coefficients" parameter specifies the number of coefficients that follow +and define the first order wavelength dispersion function. The +coefficients and functions are described below. + +The numerical values following the "coefficients" parameter, shown in +the order in which they appear, have the following meaning. + +.nf + type Function type: 1=chebychev, 2=legendre + xpow Highest power of x + opow Highest power of o + xterms Type of cross terms: Always 1 for echelle functions + xmin Minimum x for normalization + xmax Maximum x for normalization + omin Minimum o for normalization + omax Maximum o for normalization + Cmn Coefficients: m=0-xpow, n=0-opow, m varies first +.fi + +The functions are evaluated by a sum over m and n up to the specified +highest powers. + +.nf + (3) f(x,o) = sum {Cmn * Pm * Pn} m=0-xpow, n=0-opow +.fi + +The Cmn are the coefficients of the polynomial terms Pm and Pn which +are defined as follows. + +.nf + Chebyshev: + xnorm = (2 * x - (xmax + xmin)) / (xmax - xmin) + P0 = 1.0 + P1 = xnorm + Pm+1 = 2.0 * xnorm * Pm - Pm-1 + + onorm = (2 * o - (omax + omin)) / (omax - omin) + P0 = 1.0 + P1 = onorm + Pn+1 = 2.0 * onorm * Pn - Pn-1 + + Legendre: + xnorm = (2 * x - (xmax + xmin)) / (xmax - xmin) + P0 = 1.0 + P1 = xnorm + Pm+1 = ((2m + 1) * xnorm * Pm - m * Pm-1)/ (m + 1) + + onorm = (2 * o - (omax + omin)) / (omax - omin) + P0 = 1.0 + P1 = onorm + Pn+1 = ((2n + 1) * onorm * Pn - n * Pn-1)/ (n + 1) +.fi + +Note that the polynomial terms are obtained by first normalizing the x and +o values to the range -1 to 1 and then iteratively evaluating them. +.ih +EXAMPLES +Because this task is interactive it is difficult to provide an actual +example. The following describes a typical usage on arc spectra. + + cl> ecidentify arc1.ec,arc2.ec + +.ls (1) +The database is searched for an entry for arc1.ec. None is found and +the first order is plotted as a function of pixel coordinate. +.le +.ls (2) +Using a line identification chart or vast experience one of the +emission lines is identified and marked with the 'm' key. Using the +cursor position a center is found by the centering algorithm. The +aperture number, pixel position, wavelength (which is currently the +same as the pixel position), and a prompt for the true value with the +default value INDEF is printed. The true wavelength is typed in and the +status line is redrawn with the information for the feature. +.le +.ls (3) +The orders are changed with the 'j', 'k', or 'o' key and further lines are +identified with the 'm' key. +.le +.ls (4) +After a number of lines have been marked spanning the full range of the orders +and pixel coordinates the key 'l' is typed. The program now fits a preliminary +dispersion solution using the current function and function orders. Using this +function it examines each line in the line list and checks to see if there is +an emission line at that point. With many orders and lots of lines this may +take some time. After additional lines have been identified (up to +\fImaxfeatures\fR lines) the function is refit. Finally the current order +is regraphed in user coordinates. +.le +.ls (5) +Again we look at some orders and see if the automatic line identifications +make sense. +.le +.ls (6) +We next enter the dispersion function fitting mode with 'f'. A plot of the +residuals vs. pixel position is drawn. Some obvious misidentifications may +be deleted with the 'd' key. One way to proceed with determining the +function orders is to start at the lowest orders (xorder = 2 for linear +and yorder = 1 for no order dependence beyond the basic dependence). We then +increase each order one at a time. The x axis is changed between order +number and pixel position using the 'x' key to see the dependence on each +dimension. The orders are increased until there are no systematic trends +apparent. Normally the y order (for the aperture or order number dependence) +is low such as 2 to 4 while the x order (for the dispersion direction) is +whatever is needed to account for distortions. Also one can prune deviant +points with the 'd' key. Note that the order offset derived from the +aperture number is given in the title block along with the RMS. When done +we exit with 'q'. +.le +.ls (7) +The new function fit is then evaluated for all orders and the current order +is redrawn based on the new dispersion. Note also that the status line +information for the current feature has both the fitted wavelength and the +user identified wavelength. We can add or delete lines and iterate with the +fitting until we are happy with the feature list and dispersion function. +.le +.ls (8) +Typing 'q' exits the graph and prints a query about saving the information +in the database. We answer yes to this query. Note that information can +also be saved while still in the graphics loop using ":write". +.le +.ls (9) +The next image in the list is then graphed but the last dispersion solution +and feature list is maintained. If the shift is small for the new arc we +type 'a' 'c' to recenter all the features. This does not refit the dispersion +automatically so we then do 'f'. Alternatively, we could use the 's' or 'x' +keys to determine a large shift and do the recentering. +.le +.ls (10) +Finally we can exit with 'q' or examine further images with the ":image" +command. +.le +.ih +REVISIONS +.ls ECIDENTIFY V2.11 +The dispersion units are now determined from a user parameter, +the coordinate list, or the database entry. +.le +.ih +SEE ALSO +apsum, center1d, gtools, ecreidentify, identify +.endhelp |