Vis5D can work with data organized as a 5-D rectangle. The first 3 dimensions are spatial: rows, columns, and levels (or latitutude, longitude, and height). The 4th dimension is time. The 5th dimension is the enumeration of multiple physical variables such as temperature, pressure, water content, etc. In addition to the data itself, there are a number of parameters needed to describe a Vis5D dataset: the sizes of the five dimensions (number of rows, columns, levels, timesteps, and variables), geographic position and orientation of the data (map projection), the names of the variables, the actual times and dates associated with each timestep, etc. The Vis5d visualization program accepts two standard file formats: v5d files and comp5d files. Both store 3-D data in a compressed format which vis5d can use quickly and efficiently. Comp5d files are those which were produced by the comp5d program in previous versions of Vis5D. The v5d file format is the new, and prefered, file format used in version 4.0 and later of Vis5D. It is intended to be a replacement for the comp5d format because it more flexible and may be extended in the future. Vis5d can also accept a user defined file format. A user can create a new file format and the functions to read this format. See section 3.4 below. To view your data with vis5d you will typically write a conversion program to convert your data files to v5d format. To help you do this we've included four sample conversion programs to guide you. Basically, you just add the instructions to read your file format, we provide the instructions to write the v5d file. See section 3.1 below. You then link your program with -lv5d (the installed libv5d library). If you have used Vis5D in the past, you may continue to convert your data to McIDAS format and use comp5d to make a compressed file. However, to take full advantage of the new map projections and vertical coordinate system in version 4.0 and higher, you should write a new conversion program to make v5d files. Another option for getting your data into Vis5D is the v5dimport utility. v5dimport is a program for file conversion, combining, and resampling. It reads a number of different file formats and can be extended to read new formats. See chapter 7 for more details. If your data is in HDF5 format, you may find the h5tov5d conversion program useful; it is available as part of the free h5utils package. Vis5D can also work with non-gridded data. This type of data is stored as records. Each record has a geographic location and a set of variables containing character or numerical data. Vis5D does not have it's own file format for this irregular data. The two methods for getting irregular data into Vis5D are using the current irregular import program to read certain NetCDF files, or creating a new import process using calls from the irregular_v5d library. See section 3.5 for more details. Files in the v5d format are created with functions from the v5d library. We've included four sample conversion programs which outline how to make a v5d file. They are located in the convert/ subdirectory. You can choose which one to use as a template for your data converter: foo_to_v5d.f A Fortran program which assumes a rectangular lat/lon map projection and equally spaced linear vertical coordinate system. foo2_to_v5d.f A Fortran program which allows any map projection and vertical coordinate system as well as a different number of vertical levels for each variable. foo_to_v5d.c A C program which assumes a rectangular lat/lon map projection and equally spaced linear vertical coordinate system. foo2_to_v5d.c A C program which allows any map projection and vertical coordinate system as well as a different number of vertical levels for each variable. The files in the convert/ subdirectory link directly with the object and header files in the src/ directory. In your own program, you'll want to instead link with -lv5d (the installed libv5d library) and include the installed headers via: #include <vis5d/v5d.h> In any case, each conversion program uses three functions to write the v5d file: v5dCreate (or v5dCreateSimple), v5dWrite, and v5dClose. v5dCreateSimple is used to create v5d files that only specify the most basic parameters. v5dCreate allows more complicated parameters. There are versions of these functions for C and Fortran programs. Here are the descriptions of the v5dCreate and v5dCreateSimple functions in a format similar to man page documentation. C programmers should note that in the argument descriptions we describe arrays by Fortran convention, i.e. A(1) is the first element of A, whereas in C this would be A[0]. Fortran-callable functions: integer function v5dcreatesimple( name, numtimes, numvars, nr, nc, nl, varname, timestamp, datestamp, northlat, latinc, westlon, loninc, bottomhgt, hgtinc ) character* (*) name integer numtimes integer numvars integer nr integer nc integer nl character*10 varname(MAXVARS) integer timestamp(*) integer datestamp(*) real northlat real latinc real westlon real loninc real bottomhgt real hgtinc integer function v5dcreate( name, numtimes, numvars, nr, nc, nl, varname, timestamp, datestamp, compress, projection, proj_args, vertical, vert_args ) character* (*) name integer numtimes, numvars integer nr integer nc integer nl(*) character*10 varname(MAXVARS) integer timestamp(*) integer datestamp(*) integer compress integer projection real proj_args(*) integer vertical real vert_args(*) C-callable functions: int v5dCreateSimple( name, numtimes, numvars, nr, nc, nl, varname, timestamp, datestamp, northlat, latinc, westlon, loninc, bottomhgt, hgtinc ) char *name; int numtimes; int numvars; int nr, nc, nl; char varname[MAXVARS][10]; int timestamp[], datestamp[]; float northlat, latinc; float westlon, loninc; float bottomhgt, hgtinc; int v5dCreate( name, numtimes, numvars, nr, nc, nl, varname, timestamp, datestamp, compress, projection, proj_args, vertical, vert_args ) char *name; int numtimes, numvars; int nr, nc, nl[]; char varname[MAXVARS][10]; int timestamp[], datestamp[]; int compress; int projection; float proj_args[]; int vertical; float vert_args[]; name The name of the v5d file to create numtimes Number of timesteps (at least 1) numvars Number of variables (at least 1) nr Number of rows in all 3-D grids (at least 2) nc Number of columns in all 3-D grids (at least 2) varname Array of variable names: varname(1) = name of first variable varname(2) = name of second variable ... varname(numvars) = name of last variable timestamp Array of time labels for the timesteps in HHMMSS format: timestamp(1) = time of first timestep timestamp(2) = time of second timestep ... timestamp(numtimes) = time of last timestep datestamp Array of date labels for the timesteps in YYDDD format datestamp(1) = date of first timestep datestamp(2) = date of second timestep ... datestamp(numtimes) = date of last timestep nl Number of levels in all 3-D grids (at least 1) northlat Latitude of northern edge of box in degrees latinc increment between rows in degrees (positive) westlon Longitude of western edge of box in degrees (positive Westlongitude) loninc Increment between columns in degrees (positive) bottomhgt Bottom boundary of box in km hgtinc Increment between levels in km (positive) nl Number of levels in the 3-D grids per variable: nl(1) = number of levels for first variable nl(2) = number of levels for second variable ... nl(numvars) = number of levels for last variable compress Compression mode (1, 2 or 4 bytes per grid point) projection Indicates type of map projection: 0 = linear, rectangular, generic units 1 = linear, rectangular, cylindrical-equidistant 2 = Lambert Conformal 3 = Stereographic 4 = Rotated proj_args Projection arguments: if projection=0 then proj_args(1) = North boundary of 3-D box proj_args(2) = West boundary of 3-D box proj_args(3) = Increment between rows proj_args(4) = Increment between columns else if projection=1 then proj_args(1) = North Latitude bound of 3-D box proj_args(2) = West Longitude bound of 3-D box proj_args(3) = Increment between rows in degrees proj_args(4) = Increment between cols in degrees else if projection=2 then proj_args(1) = Standard Latitude 1 proj_args(2) = Standard Latitude 2 proj_args(3) = Row of North/South pole proj_args(4) = Column of North/South pole proj_args(5) = Longitude parallel to columns proj_args(6) = Increment between columns in km else if projection=3 then proj_args(1) = Latitude of center (degrees) proj_args(2) = Longitude of center (degrees) proj_args(3) = Row of center of projection proj_args(4) = Column of center of projection proj_args(5) = Spacing between columns at center else if projection=4 then proj_args(1) = North boundary on rotated sphere proj_args(2) = West boundary on rotated sphere proj_args(3) = Increment between rows proj_args(4) = Increment between columns proj_args(5) = Earth Latitude corresponding to (0,0) proj_args(6) = Earth Longitude corresponding to (0,0) proj_args(7) = Rotation angle endif vertical Indicates type of vertical coordinate system: 0 = equally spaced levels in generic units 1 = equally spaced levels in km 2 = unequally spaced levels in km 3 = unequally spaced levels in mb vert_args Vertical coordinate system arguments: if vertical=0 then vert_args(1) = height of bottom level vert_args(2) = spacing between levels else if vertical=1 then vert_args(1) = height of bottom level in km vert_args(2) = spacing between levels in km else if vertical=2 then vert_args(1) = height (km) of grid level 1 (bottom) vert_args(2) = height (km) of grid level 2 ... vert_args(N) = height (km) of grid level N (top) where N is the maximum value in the nl array. else if vertical=3 then vert_args(1) = pressure (mb) of grid level 1 (bottom) vert_args(2) = pressure (mb) of grid level 2 ... vert_args(N) = pressure (mb) of grid level N (top) where N is the maximum value in the nl array. endif The v5dWrite function is used to write a single 3-D grid of data to a v5d file. The grid is identified by a timestep and physical variable number. Here is the synopsis of v5dWrite: Fortran-callable function: integer function v5dwrite( time, var, data ) integer time integer var real data(*) C-callable function: int v5dWrite( time, var, data ) int time; int var; float data[]; time A timestep number in the range [1..numtimes] var A variable number in the range [1..numvars] data 3-D array of grid values; number of values = nr*nc*nl(var) ordered as data[row+nr*(col+nc*lev)] where row increases from North to South, col increases from West to East, and lev increases from bottom to top The v5dClose function closes the v5d file after the last grid has been written. No arguments are needed. Here is the synpsis of v5dClose: Fortran-callable function: integer function v5dclose C-callable function: int v5dClose() Each of the create functions returns 1 when successful and 0 when an error occurs. Looking at any of the example data conversion programs, you'll see that there are variables which directly correspond to the arguments to v5dCreate/v5dCreateSimple. It is up to you to initialize these variables. For example, you'll have to assign to numtimes the number of timesteps in your dataset, assign to numvars the number of variables in your dataset, etc. After you've initialized all these variables, the v5dCreate (or v5dCreateSimple) call will create the v5d file. If you've failed to initialize any of the variables you will see an appropriate error message. Next, the conversion program will enter a nested loop inside of which you must insert the code to read your data for the appropriate time step and physical variable number. Read your data into the array specified. The v5dWrite call will then compress and write the data to the v5d file. Finally, the v5dClose function will be called after all the data has been written. After you've written and compiled your file converter, you should test it with one of your data files then check that it worked by running the v5dinfo and v5dstats utility programs on the v5d file. If everything looks OK, try running vis5d. Here is an example of typical values that might be assigned to each variable if one were using the foo_to_v5d.f program: Assignment Comments numtimes = 5 5 time steps numvars = 4 4 physical variables nr = 30 30 rows in each 3-D grid nc = 40 40 columns in each 3-D grid nl = 20 20 levels in each 3-D grid varname(1) = "U" U (east/west) wind component varname(2) = "V" V (north/south) wind component varname(3) = "T" Temperature varname(4) = "P" Pressure timestamp(1) = 140000 2:00:00 pm timestamp(2) = 141500 2:15:00 pm timestamp(3) = 143000 2:30:00 pm timestamp(4) = 144500 2:45:00 pm timestamp(5) = 150000 3:00:00 pm datestamp(1) = 94036 36th day of 1994 (February 5) datestamp(2) = 94036 " datestamp(3) = 94036 " datestamp(4) = 94036 " datestamp(5) = 94036 " northlat = 60.0 Northern boundary of box is at 30 degrees latitude latinc = 1.0 There is 1 degree of latitude between each of the 30 rows westlon = 100.0 Western boundary of 3-D box is at 100 degrees longitude loninc = 0.5 0.5 degree of longitude between each of the 40 columns bottomhgt = 0.0 Bottom of box is at 0km (sea level) hgtinc = 1.0 1 km between each of the 20 grid levels (top at 19.0km) The product of the number of rows, columns, levels, timesteps, and variables is the total number of data points. In this example: 30*40*20*5*4 = 480,000. A real dataset may be 100 rows by 100 columns by 20 levels, have 50 timesteps, and 10 variables for a total of 100,000,000 data points. The difference between the foo_to_v5d program (which uses v5dCreateSimple), and the foo2_to_v5d program (which uses v5dCreate), is the later allows you to specify any map projection, vertical coordinate system, a different number of grid levels for each physical variable, and to control data compression. To specify a map projection, you must set the value of projection to 0,1,2 or 3 to indicate which projection, then specify the projection-dependent parameters in the proj_args arrray. Specifying the vertical coordinate system is done similarly. It is sometimes useful to specify a different number of grid levels for each variable. For example, suppose most of your variables have 30 grid levels but a some variables have fewer grid levels, perhaps only one. Prior to version 4.0 of Vis5D, you would have had to fill in the extra levels with redundant, missing or dummy data values. With the v5dCreate function you can specify how many grid levels are present for each individual physical variable with the nl array parameter. Be aware that the amount of data passed to the v5dWrite call will depend on which variable you're writing. For example, if your grid has C columns and R rows then the number of values in the data array passed to v5dWrite for variable V must equal C*R*nl(V). By default, the bottom-most grid level of each variable is displayed at the bottom of the 3-D box; each grid extends upward for how ever many levels are present. Sometimes, however, the bottom-most grid level of a particular variable should be positioned higher up. An example of this is a combined ocean/atmosphere dataset. There may be a total of 18 grid levels: the bottom 8 grid levels being ocean data and the top 10 grid levels being atmospheric data. In this case, the bottom of the atmospheric data should be offset or shifted upward by 8 grid levels. Elaborating on the ocean/atmosphere example, suppose we have 2 ocean variables named S (salinity) and T (temperature) and 2 atmosphere variables named P (pressure) and T1 (temperature). There are 8 layers of ocean data and 10 layers of atmospheric data. Here is a summary showing how the lowlev array is the solution to this situation: varnum varname(varnum) nl(varnum) lowlev(varnum) 1 S 8 0 2 T 8 0 3 P 10 8 4 T1 10 8 The lowlev array is not specified in the v5dCreate function because it was developed after the v5dCreate function was well established. Instead, the new v5dSetLowLev function is called with the lowlev array. This separate function was added to extend the functionality of v5dCreate without changing its calling sequence. Here is the synopsis of v5dSetLowLev: Fortran-callable function: integer function v5dsetlowlev( lowlev ) integer lowlev(*) C-callable function: int v5dSetLowLev( lowlev ) int lowlev[]; Argument description: lowlev: Specifies the vertical offset, in grid levels, for each variable. lowlev(1) = offset for first variable lowlev(2) = offset for second variable ... = ... lowlev(numvars) = offset for last variable v5dSetLowLev may be called at any point between v5dCreate and v5dClose. The v5dCreate and v5dcreate functions allow you to control how the grid data are compressed. The default is for grid values to be linearly scaled to one byte integers. This works very well for most data sets, since the scaling factors are chosen independently for each combination of time step, variable and vertical level. Furthermore, the compression to one byte per grid point enables Vis5D's high degree of interactivity, since compression allows entire data sets to be resident in memory. However, the compress argument of the v5dCreate and v5dcreate functions lets you pick whether grid point values are scaled to 1-byte integers, scaled to 2-byte integers, or left as 4-byte floating point values (no compression). We recommend that you try compression to 1-byte integers first, and only use 2 or 4 bytes if you have precision problems at 1-byte. Vis5D version 4.2 and later allow you to specify the physical units for each variable in your dataset. The v5dSetUnits() function takes two arguments: a variable number and a units character string. If the first variable in your file is P and the units are millibars then you can specify that with: C: v5dSetUnits( 1, "millibars" ) Fortran: call v5dsetunits( 1, "millibars" ) The units will be displayed by the v5dinfo program and in Vis5D when using the probe. To compile your program which uses v5dCreate, v5dWrite, and v5dClose you must link with the src/v5d.o and src/binio.o files. Alternatively, link with -lv5d to link with the installed libv5d library. See the makefiles in the convert/ directory for examples. Finally, if your data is generated by an atmospheric or oceanic model, you may want to consider modifying your model to generate v5d files directly using the v5dCreate, v5dWrite, and v5dClose functions. Look at the sample data conversion programs for ideas. Version 4.0 of Vis5D added support for new map projections and vertical coordinate systems. When we use the term map projection, we're referring to the relationship between the rows and columns of data in the 3-D grid to the latitude/longitude of the earth. The term vertical coordinate system refers to the relationship between the vertical levels of data in the 3-D grid to altitude in the atmosphere (or depth in the ocean). Vis5D 5.2 supports the following map projections: This is a linear, regularly-spaced coordinate system with no implied units. This system is useful when your data is not related to earth science (computational fluid dynamics for example.) North/south coordinates increase upward and east/west coordinates increase to the left. The projection is defined by four parameters: NorthBound: Northern boundary of 3-D box WestBound: Western boundary of 3-D box RowInc: Increment (spacing) between grid columns ColInc: Increment (spacing) between grid rows Example: Suppose your 3-D grid has 80 rows and 60 columns and NorthBound = 100.0 meters, WestBound = 50.0 meters, RowInc = 0.5 meters, and ColInc = 0.5 meters, then: the south boundary will be at 60.5 meters, i.e. southbound = NorthBound - (RowInc * (rows-1)) and the east boundary will be at 20.5 meters, i.e. eastbound = WestBound - (ColInc * (columns-1)) This is the rectangular latitude/longitude coordinate system used in previous versions of Vis5D. Latitude increases to the North (upward in the graphical display) and longitude increases to the West (leftward in the graphical display; positive west latitude). The projection is defined by four parameters: NorthBound: Northern boundary of 3-D box in degrees of latitude in therange [-90S,90N]. WestBound: Western boundary of 3-D box in degrees of longitude in therange [-180E,180W]. RowInc: Increment (spacing) between grid rows in degrees of latitude greater than zero. ColInc: Increment (spacing) between grid columns in degrees of longitude greater than zero. Example: If your 3-D grid has 30 rows and 60 columns and if NorthBound = 70.0, WestBound = 140.0, RowInc = 1.0, and ColInc = 0.5, then: the south boundary will be at 41 degrees latitude. i.e. (NorthBound - RowInc * (rows-1)) and the east boundary will be at 110.5 degrees longitude. i.e. (WestBound - ColInc * (columns-1)) This is a conic projection defined by the following six parameters. Lat1, Lat2: First and second standard latitudes in the range [-90S,90N]. Lat1 and Lat2 define where the imaginary cone intersects the sphere of the Earth. Lat1 and Lat2 must have the same sign, that is, they must both be positive or both negative. Also, Lat1 must be greater than or equal to Lat2. PoleRow, PoleCol: These parameters indicate the position of the north or south pole with respect to the 3-D grid coordinate system. These values may be outside the 3-D grid. If Lat1 and Lat2 are positive, the north pole is assumed, else, the south pole is assumed. CentLon: Central longitude: this parameter indicates which Earth longitude is to be parallel to the 3-D grid columns. ColInc: Increment (spacing) between grid columns at the central longitude and standard latitudes, in km. This parameter controls the scale of the projection. Example 1: Suppose your 3-D grid has 35 rows and 40 columns and you want a Lambert conformal projection of the United States centered over Wisconsin: Lat1 = 70.0 Lat2 = 20.0 PoleRow = -35.0 PoleCol = 20.0 Central Longitude = 90.0 ColInc = 100.0 Example 2: Suppose your 3-D grid has 35 rows and 40 columns and you want a Lambert conformal projection over Australia: Lat1 = -20.0 Lat2 = -70.0 PoleRow = 60.0 PoleCol = 20.0 Central Longitude = -130.0 ColInc = 200.0 Beware that when the pole is visible in a Lambert conformal projection, there is usually a wedge-shaped region (with its apex at the pole) which is undefined (i.e. Longitude is >180 AND <-180). In this region, there will be no map lines and the topography will be incorrect. An aximuthal stereographic projection defined by five parameters: CentLat, CentLon: Latitude and longitude of the center of projection. The apex of the imaginary cone will be over this coordinate. CentRow, CentCol: Row and column of the center of projection. The grid row and column indicated will be at the center of the projection. These values may be outside the 3-D box. ColInc: Increment (spacing) between grid columns in km at the center of the projection. This parameter controls the scale of the projection. Example: Suppose your 3-D grid has 40 rows and 40 columns and want an azimuthal stereographic projection centered over of the north pole: CentLat = 90.0 CentLon = 0.0 CentRow = 20.0 CentCol = 20.0 ColInc = 200.0 This is the rectangular latitude/longitude coordinate system on a sphere rotated with respect to the Earth's natural latitude/longitude. North/south coordinates increase upward on the rotated sphere and east/west coordinates increase leftward on the rotated sphere. The projection is defined by seven parameters: NorthBound: Northern boundary of 3-D box in degrees of latitude in the range [-90S,90N]. WestBound: Western boundary of 3-D box in degrees of longitude in the range [-180E,180W]. RowInc: Increment (spacing) between grid rows in degrees of latitude greater than zero. ColInc: Increment (spacing) between grid columns in degrees of longitude greater than zero. CentLat, CentLon: Latitude and longitude on Earth corresponding to Latitude/Longitude = (0,0) on the rotated sphere. Rotation: Clockwise angle of rotation of rotated sphere about its (0,0) point. Example: Over small regions the Earth is nearly flat and we can exploit this to create nearly square grids for small scale models. We can generate a nearly square grid of 41 rows by 41 columns over a small region over Wisconsin with: NorthBound = 2.0 WestBound = 2.0 RowInc = 0.1 ColInc = 0.1 CentLat = 43.0 CentLon = 90.0 Rotation = 0.0 Vis5D 5.2 supports the following vertical coordinate systems: This is a linear vertical coordinate system in which levels in the 3-D grid are equally spaced. No specific units are implied. The coordinate system is defined by two parameters: BottomBound: Bottom boundary boundary of 3-D box. LevInc: Increment(spacing) between grid levels. Example: Suppose your 3-D grid has 20 levels and you want the bottom boundary to be 0.0 meters and you want .1 meters between levels. Then: BottomBound = 0.0 LevInc = 0.1 This is a linear vertical coordinate system used in previous versions of Vis5D. Grid levels are equally spaced. The coordinate system is defined by two parameters: BottomBound: Bottom boundary of 3-D box in km. LevInc: Increment (spacing) between grid levels in km greater than zero. Example: Suppose your 3-D grid has 20 levels and you want .5 kilometers between grid levels. Then: BottomBound = 0.0 LevInc = 0.5 This is a linear vertical coordinate system in which grid levels can be unequally spaced. The coordinate system is defined by an array of N height parameters where N is the number of levels in the 3-D grids. If the number of grid levels is different for each variable, N is the maximum number of grid levels. Height(1): Height of first (bottom) grid level in km Height(2): Height of second grid level in km ... ... Height(N): Height of Nth (top) grid level in km Note that the Height values must increase with N. Example: Suppose your 3-D grids have 10 levels and you want the grid levels to be more closely spaced near the bottom than near the top. Then: Height(1) = 0.0 Height(2) = 0.1 Height(3) = 0.2 Height(4) = 0.3 Height(5) = 0.4 Height(6) = 0.6 Height(7) = 0.8 Height(8) = 1.0 Height(9) = 1.3 Height(10) = 1.6 It is also possible to display the vertical axis on a logarithmic scale. This is done with the -log command line option when you start vis5d. In this case, the vertical axis is logarithmic with respect to height but linear with respect to pressure. The relationship between height (H) and pressure (P) is: P = 1012.5 * exp[ H / -7.2 ] H = -7.2 * Ln[ P / 1012.5 ] The constants 1012.5 and -7.2 are just defaults which can be overriden when you specify the -log option. See section 6.1 for details. This is a linear vertical coordinate system in which grid levels can be unequally spaced. The coordinate system is defined by an array of N pressure parameters where N is the number of levels in the 3-D grids. If the number of grid levels is different for each variable, N is the maximum number of grid levels. Pressure(1): Pressure of first (bottom) grid level in km Pressure(2): Pressure of second grid level in km ... ... Pressure(N): Pressure of Nth (top) grid level in km Note that the Pressure values must decrease with N. For the purposes of calculating wind trajectories, Vis5D assumes the relationship between height (H) and pressure (P) is: P = 1012.5 * exp[ H / -7.2 ] H = -7.2 * Ln[ P / 1012.5 ] Only the v5d file format is capable of storing the new map projection and vertical coordinate system information. When a v5d file is read into vis5d this information is used to setup the topography, map lines, and compute wind trajectories. The vis5d program also supports two other display projections: spherical and cylindrical. Instead of drawing a rectangular 3-D box, these projections will actually warp the 3-D box into a spherical or cylincrical shape. These projections are used by specifying the -projection option with the value spherical or cylindrical; they are not specified in the v5d file. The spherical option can be used to display your data on a 3-D globe. The cylindrical option can be used to display your data on a flat, round topography. It's probably best to just experiment with these options using the LAMPS dataset for example. See the section on Vis5d's command line options for more information. Analysis and visualization of wind information is an important part of Vis5D. Specifically, the vis5d program looks to see if your data set contains variables named U, V and W. If present, they are assumed to be the three components of wind vectors and are used to display trajectory tracings and wind slices. The U wind component is parallel to rows, with positive U values pointing toward increasing column numbers (i.e., positive eastward in a cylindrical equidistant map projection). The V wind component is parallel to columns, with positive V values pointing toward decreasing row numbers (i.e., positive northwardward in a cylindrical equidistant map projection). Positive W values are upward, negative W is downward. The units for U, V and W are assumed to be meters per second except when a generic map projection or vertical coordinate system is used. In that case, the units are in X per second where X is the units used to specify the northbound, westbound, rowinc, and colinc parameters. If you do not like to use U, V, and W for wind vector components you can either specify other wind variable names on the vis5d command line or enter them while running vis5d. Strictly speaking, U, V and W do not have to represent wind motion. They can be used to represent any flow field such as ocean currents. However, you may want to scale U, V, and W by some constant for visualization purposes. Vis5D allows any grid data value to be undefined or 'missing'. For example, datasets based on observations are often incomplete or contain erroneous values. In your data conversion program you can indicate a grid value is missing by assigning it a value greater than 1.0e30. Missing data in vis5d will show up as holes in isosurfaces and contour slices and as black regions in colored slices. The data probe will report missing values as 'Missing'. This section is intended for experienced programmers. In order to allow the reading of a different file format the functions in /vis5d-5.2/src/user_data.c must be changed. There are two functions in user_data.c which need to be changed, user_data_get_header and user_data_get_grid. There is currently sample code in both of these functions to use as a template to create a new data file format. The sample code reads the sample user data in /vis5d-5.2/user_data. A user can also define new topography and map file formats. In order to read a new topography file format the function user_data_get_topo must be changed, and for a new map file format the function user_data_get_map must be changed. Both of these functions are also found in /vis5d-5.2/src/user_data.c and they both have sample code. In order to invoke the reading of new file format for data, topography or map files the command line option -userdata followed by a 'G' (for grid data), 'M' (for map data) and/or 'T' (for topography data). For example to use the sample code in user_data.c to read grid data and topography data, the following line would be used: vis5d user_data/ETA.dat -user_data GT -topo user_data/ETA_TOPO.dat One method for getting irregular data into vis5d is to use the irregular importer. The 'IRG IMPORT' button can be found on the Vis5D control panel which will invoke the irregular importer. The control panel will be brought up when loading a regular v5d file or it can be brought up by typing vis5d -nofile In the importer there is a "File List." Pressing the "Load File..." button will bring up a file browser where one can select the NetCDF files to load. Any number of NetCDF files may be loaded at one time. Once these files are loaded a list of unique times and variables will be created and displayed. The user can highlight/unhighlight desired times and variables. Frequently there may be a large number of times which do not contain much data. The "FILTER" button can be used to quickly select certain times. Once the desired files have been selected the user will need to assign a "Dataset Name" and select the memory pool size (default 32M). The "Load" button will then load the selected files and data into vis5d. The irregular importer can currently read three types of NetCDF files. The first type of file is created by translating the Aviation Routine Weather Reports (METARs) and the Aviation Selected Special Reports (SPECIs) to NetCDF format, using the Unidata decoders . More information about these decoders and METAR data can be found at the Unidata web site. The other two types of data that can be read are METARs converted to the FSL (Forecast Systems Laboratory) NetCDF format and profiles which are also converted to the FSL NetCDF format. It is possible to read other NetCDF formats with the irregular importer but it requires the addition of source code to the importer. If one is familiar with C programming and the NetCDF file structure it would not be a hard task. The two files: file.c and iapi.c would require the additions and they are found in the source code. Sample METAR data in both the Unidata and FSL formats can be downloaded. This tar file also contains a gridded v5d file of an NGM model run. The time frame of this v5d file coincides with the Unidata METAR files. One can overlay both a regular v5d data set and an irregular data set in the same display. The second method for incorporating irregular data into vis5d is the creation of a new import program or converter. This program would read the user's file format and insert the data into vis5d via the irregular_v5d library calls. The functions that would need to be called and information about them are found in the src file /vis5d-5.2/src/irregular_v5d.c. This route for getting irregular data into vis5d is suggested for experienced programmers only.