GPLOT recipes: Position-velocity diagram

The image shows a XV-diagram with a profile overlay. The XV contour plot represents data that is extracted from a data cube with program SLICE. The profile data is extracted from a cube that was made with program MOMENTS. In this recipe, we will explain how the plots are scaled.

The GPLOT macro:

With program SLICE you create a new data cube with a width equal to the number of sample points in the slice, height equal to the number of slices and depth equal to the number of velocities. An 'XV' diagram can be plotted after you selected a subset at a certain declination (which is not a real declination anymore after SLICE). The (sliced) input in our example is: inset sliceset d 0. Program SLICE displays for each slice the start and end position of the slice. This information is also stored in a GDS-table in the header of the set made by SLICE. The column names are SLXMIN, SLXMAX, SLYMIN, SLYMAX. In this example SLICE displayed Slice #1 starts at (-16 -60) and ends at (16 61). These are numbers that we have to remember if command profile is going to be used to overlay other data.
Two subsets, containing velocity information, were produced by MOMENTS. The first one is subset inset u10310s30-2dim 3. It contains velocities measured at peaks in the velocity profiles (in the same original data cube used in SLICE). Subset inset u10310s30-2dim 7 contains intensity weighted mean velocities. If you want to overlay data in these subsets taken along the same slice as used in SLICE, then we need the profile command followed by prodata to copy . It is necessary to use the profile command with the same start and end point as the grid positions between which the slice was taken. Here are the commands:

erase                           ! Clear screen
colour foreground               ! Default colour is foreground colour
inset sliceset d 0              ! XV diagram taken from slice.
box -64 650 km/s 63 770 km/s    ! Limits for that XV diagram
The box command needs some attention here. The range in x-direction must be the full axis length. This is important because start and end point of slice and profile in x direction must coincide. The limits in y direction are arbitrary. They have to correspond with the range in profile y values. But for the profile, the y values are stored as physical coordinates (velocities) so in the box command the y limits are entered as numbers followed by the physical units of the y axis.
level 0.8 2 3                   ! Contours for XV
xsize 120                       ! Size in x is 120 mm
ysize 80
frame                           ! Plot the axis with default labels
conto                           ! Plot the contours
inset u10310s30-2dim 3          ! First subset to extract profile from
profile -16 -60 16 61           ! Start end end point of profile
profdata                        ! Copy profile data in xcolumn & ycolumn
colour green    
xrange xcolumn                  ! Limits are min/max of xcolumn data
xsize 120                       ! Scale this length also to 120 mm !!!
yrange 650 770                  ! Limits in y
ysize 80
symbol 17                       ! Filled dot
points                          ! Plot the points in this profile
connect                         ! Connect all non blank profile points
inset u10310s30-2dim 7          ! Second subset (int. weighted mean vel.)
profile -16 -60 16 61
profdata                        ! Copy profile data in xcolumn & ycolumn
colour red
symbol 13                       ! Filled triangle
xrange xcolumn
xsize 120
yrange 650 770
ysize 80