1NCVIEW(1) General Commands Manual NCVIEW(1)
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6 ncview - graphically display netCDF files under X windows
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9 ncview [-beep] [-copying] [-frames] [-warranty] [-private] [-ncolors
10 XX] [-extrainfo] [-mtitle "title"] [-minmax fast | med | slow | all]
11 datafiles ...
12
14 Ncview displays 2-D slices of a netCDF data file, using the X Window
15 System graphical user interface (Release 4 or higher). You can examine
16 different floating point variables in the file, and animate the float‐
17 ing point data along the ``record dimension'' (usually time) to see how
18 it evolves. You can also display 1-D (line plot) views of the data
19 simply by clicking the mouse on the point of interest.
20 When you first invoke ncview, a command panel comes up which has a num‐
22 ber of buttons for manipulating the current view into the data file,
23 and presenting various information about the current view. From the
24 top, going down, the information fields are: the 'title' of the data
25 file; the 'long_name' of the currently selected variable; the frame
26 number (i.e., place along the scan axis) currently displayed; the mini‐
27 mum and maximum values of the variable; and the value of the data point
28 under the cursor (only active when the pointer is over the color con‐
29 tour image).
30 Next comes a row of buttons similar to a tape recorder, used for chang‐
32 ing the view into the netCDF file along the scan dimension. In Version
33 1.XX of ncview, the scan dimension is constrained to be the ``record
34 dimension'' (in netCDF parlance). From the left, the buttons are: the
35 quit button; a button to take you directly to the first frame, marked
36 "->1"; rewind, which loops the images going backwards; step backwards;
37 pause; step forwards; and fast forward, which loops the images going
38 forwards.
39 Below this is the row of option buttons, which from the left are: the
41 colormap button, labeled with the name of the current colormap (see
42 below); "Inv P", which inverts the physical representation of the data
43 (flips it upside-down); "Inv C", which inverts the colors currently
44 being used so that the colors indicating minimum and maximum are
45 switched; the magnification button, which sets how much image expansion
46 the image undergoes; and the transformation button, which determines
47 what preprocessing the data undergoes before display. For this button,
48 "Linear" means no preprocessing, "Low" means that the data is raised to
49 the fourth power before conversion to a pixel, so that low values are
50 emphasized; and "Hi" means that the fourth root of the data is taken
51 before conversion, so that large values are emphasized. Next comes
52 "Set Dim"; pressing this pops up a window which allows you to determine
53 which variables are shown on the X and Y axes. Note that Version 1.XX
54 of ncview will not transpose your data! This means that, for example,
55 you cannot simultaneously display the X dimension along the Y axis
56 while displaying the Y dimension along the X axis---that would be an
57 attempt to transpose the data. You can display the X dimension along
58 the Y axis if some other variable which varies less rapidly in your
59 particular data file (for example, depth) is on the X axis. Such a
60 configuration is possible because it involves no transposition of data.
61 In general you don't have to worry about this issue much, because if
62 you attempt to pick axes which would be transposing the data, ncview
63 switches them (and tells you that it's doing so!) so you can get the
64 axes you want. Note that there is never any ambiguity about which
65 dimensions are being displayed on what axes; that information is always
66 shown in the main panel. Next is "range", which pops up dialog boxes
67 to set the data min and maxes which will be contoured. Pressing with
68 the RIGHTMOST mouse button on the "range" button resets the ranges to
69 match the currently displayed slice; this is a VERY useful option, so
70 remember it and make use of it frequently! The last button shows the
71 method currently employed for expanding the data onto the screen; the
72 default, "bi-lin", performes a bi-linear interpolation. Also available
73 is "repl", which simply replicates the pixels and is somewhat faster.
74 The next row of buttons shows what variables can be displayed from the
76 input files. Note that when ncview first comes up, if there is more
77 than one variable in the file, you must select a variable to display
78 before you will see anything. If there is only one variable in the
79 file, the selection defaults to that one.
80 Below the variable selection buttons are the dimension information
82 fields. All the dimensions for the displayed variable which can take
83 on more than one value are shown here, one variable to a line. In each
84 line, there are 6 fields of information; from left to right, they are:
85 "Dim", the Dimension identifier, which is `Scan' if the dimension is
86 currently the scanned dimension (i.e., the dimension accessed via the
87 tape-recorder style buttons), `X' if the dimension appears in the color
88 contour display along the x axis, or `Y' if it appears in the color
89 display along the y axis. This field will be blank if it isn't Scan,
90 X, or Y. Next come "Name", the dimension's short name; "Min", the min‐
91 imum value of the dimension; "Current", the current value of the dimen‐
92 sion as displayed in the color contour panel; "Max", the maximum value
93 of the dimension; and "Units", the dimension's units. Clicking on the
94 "Current" field of a dimension allows you to change the current value
95 of that dimension. Clicking with the left mouse button increases the
96 current value of that dimension; clicking with the right button
97 decreases it.
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100 You can get a popup X-Y (line) graph of data at a point simply by
101 clicking on the point of interest. You have several options at this
102 point; with the bottons at the bottom of the window you can change the
103 axis along which the data is graphed (if there are other axes avail‐
104 able), use log scaling for the X and/or Y axis, and set the data range.
105 You can also dump out the data from the X-Y plot into an text file, for
106 easy importation into other programs.
107 Up to five line plots can be on one graph. The panel on which the next
109 line plot will appear is called the "locked" panel. If you don't want
110 the next line plot to appear on the locked panel, then unlock it by
111 pressing the "Locked" button. At the moment, panels are automatically
112 unlocked when you choose a new variable.
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115 ncview supports time axes that use the conventions in the udunits pack‐
116 age. Typical units names in this scheme would be "days since
117 1990-01-01". If ncview encounters a time dimension that it understands
118 in this way, then it displays the calendar date (as calculated by the
119 udunits package, not ncview) rathar than the actual axis value. For
120 instance, it might display "3_Jun_1995" rather than "Day 2390". To
121 have this functionality, the udunits package must be able to find the
122 "udunits.dat" file. You must set the environmental variable
123 UDUNITS_PATH to the location of this file for ncview to be able to find
124 it.
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127 Clicking on a button with the left mouse button invokes the standard
128 action described above; clicking with the right mouse button on the
129 colormap select, transformation, magnification, or dimension "Current"
130 buttons DECREASES the selection instead of increasing it (i.e., cycles
131 in the reverse direction). Holding down the control key "accelerates"
132 actions; while clicking with the left mouse button will increase the
133 rate at which the rewind, step backwards, step forwards, and fast for‐
134 ward keys will step through the data. When holding down the control
135 key while clicking on the magnification button, the magnification DOU‐
136 BLES or HALVES instead of incrementing or decrementing by one.
137 Ncview attempts to save the displayed images in main memory, with each
139 frame being saved as it is calculated for the first time. This speeds
140 up looping replays of the same data. If there is not enough memory to
141 store all the required frames at the selected magnification, ncview
142 will inform you and automatically stop trying to do so. Changing the
143 magnification will again force ncview to try and allocate a image buf‐
144 fer.
145 Since the scaled, interpolated pixel maps are stored, the following
147 operations will flush the image buffer and require recalculating the
148 images if they are performed: inverting the data; inverting the color
149 map; changing the magnification; changing the data transformation (lin‐
150 ear, lo, or hi); changing the dimension; changing the range; changing
151 the pixel replication scheme. Changing colormaps does not require
152 refilling the image buffer.
153 You can invoke ncview with multiple netCDF filenames on the command
155 line, and it will try to present the data in a logical way; i.e., if
156 there are identically named variables in the data files, it will try to
157 treat them as if they were all in one giant data file. If there are
158 different variables in different files, it will let you choose to dis‐
159 play any of the available variables. This is generally a Good Thing,
160 but if you have identically named variables in different files with
161 different attributes, ncview will not know which attribute you want to
162 use and most likely will crash.
163
165 It is important to set the data range correctly; otherwise, the color
166 contour might come out all red, or all blue, or otherwise not very
167 interesting. There are a number of ways to set or manipulate the
168 range: 1) Click with the left mouse button on the "range" button. This
169 pops up a dialog window letting you specify the minimum and maximum
170 values directly. 2) Click with the right mouse button on the "range"
171 button. This scales the displayed data to the currently shown frame.
172 3) Click with the left mouse button on a data point in the color-con‐
173 tour window; this will set the minimum scaling to the value of the data
174 which you clicked on. 4) Click with the right mouse button on a data
175 point in the color-contour window; this will set the maximum scaling to
176 the value of the data which you clicked on.
177
179 -beep: rings the terminal's bell when stepping forward through frames
180 in movie mode and the loop is restarted.
181 -extrainfo: Puts up extra information in the color-contour window.
183 This is useful for photographing the computer screen to make slides or
184 pictures of the data.
185 -frames: This will make ncview dump out the frames it displays in a
187 series of PPM-format files. You can then make them into an mpeg movie
188 if you so desire (using tools other than ncview).
189 -mtitle: Puts the following argument (enclosed in quotes) up as the
191 title of the color-contour window.
192 -ncolors: Sets the number of colors which will be displayed. Defaults
194 to 200. Must currently be less than 256.
195 -private: Forces use of a private colormap. This will cut down on the
197 number of colormap entries used, but will turn the rest of the screen
198 annoying colors.
199 -minmax: determines how the calculation of minimum and maximum values
201 is done. If fast, then only the first, middle, and last time entries
202 of each variable are examined. If med, then every fifth time entry is
203 scanned for extrema. If slow, then every tenth entry is used. If all,
204 then every time entry is examined for extrema. Default is "fast".
205 -copying: prints out the terms under which ncview may be copied, dis‐
207 tributed, and modified. Ncview is covered under the provisions of the
208 Gnu General Public Liicense Version 1.
209 -warranty: Ncview comes with no warranty; this option prints out a
211 fuller statement to this effect.
212
214 Ncview looks in directory /usr/share/ncview for system-wide colormap
215 (.ncmap) files. It also examines the user's environmental variable
216 NCVIEWBASE for the name of a directory which contains additional col‐
217 ormap files. If that is not defined, then colormaps are sought in the
218 user's home directory, and in the directory which was run from.
219 Colormap files have 256 lines, each consisting of one r g b triplet,
221 where r, g, and b are integers in the range of 0 to 255. There should
222 be only whitespace separating the r, g, and b values on each line.
223 Colormap files end with the extension ".ncmap". If Ncview does not
224 find any colormaps, it will complain, and supply a simple default map.
225 It is necessary to install the applications default file, "Ncview", in
227 your $XAPPLRESDIR directory for the program to function properly. If
228 the screen appears out of alignment, make sure that this installation
229 has been performed.
230 The application resources file recognizes the following resources, in
232 addition to the standard ones:
233 labelWidth
236 The width, in pixels, of the information labels at the top of
237 the main window. If you generally use long titles and variable
238 longnames, you might want to increase this. Default = 400.
239 buttonWidth
241 The width, in pixels, of the "variable" and "dimension" buttons.
242 If you use long names for these, you might want to increase this
243 value. Default = 50.
244 nVarsPerRow
246 The number of variable buttons in a row before a new one is
247 started. Set to be aesthetically pleasing to you. Default = 5.
248 deltaStep
250 The amount to step forward and backwards by when the control key
251 is held down while pushing the button. If this value is less
252 than 0, in indicates an absolute number of steps to take; if
253 this value is greater than zero, it indicates the percent (in
254 integer form, from 1 to 100) of the total file size to step.
255 Default = 10 (ten percent).
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259 Occasional bugs surface, especially when mixing variables in different
260 files.
261 Please send all bug reports to pierce@cirrus.ucsd.edu
263 local NCVIEW(1)