Resource: plot_domain

Resource plot_domain
Command Line -pd=domain
Environment Variable wxpdomain
Default Value Usually left to user prompt

The plot_domain resource is used to specify the exact domain to plot the data or contour the grid.  This resource specifies the projection, location, aspect ratio of the plot, and the size of the domain:

proj:params,clat,clon,nx,ny,dx,dy

where:

Specifying the Domain

There are several ways to specify the domain.  Not all of the above parameters need to be specified in order for the program to know what to plot

Parameters to specify  Assumed values for others
proj,plon,clat,clon,nx,ny,dx,dy  
proj:params,clat,clon,nx,ny,dx,dy  
proj,plon,clat,clon,dx,dy nx=25,ny=17
proj,clat,clon,nx,ny,dx dy=dx
proj,clat,clon,dx,dy nx=25,ny=17
proj,clat,clon,dx nx=25 ny=17 dy=dx
clat,clon,nx,ny proj=ps dx=1.2 dy=1.2
clat,clon,dx proj=ps nx=25 ny=17 dy=dx
size,nx,ny used for images
proj,clat,clon nx=25 ny=17 dx=1.2 dy=1.2
clat,clon proj=ps nx=25 ny=17 dx=1.2 dy=1.2
file:region look up domain in file
region look up domain in wxp.reg file
proj null projection

NOTE: clat,clon can be replaced by id:xxx

Selecting a Domain for a Map Projection

In selecting a plot domain, first determine the center latitude and longitude of the domain. This is centered on some meteorological event such as a low pressure system or on a station of interest. Next, determine the rough size of the domain to capture all the data of interest. This is done by estimating the horizontal size of the domain in kilometers and dividing by 100*(nx-1) to get dx and dy. By default, most plots use nx,ny of 25x17. So in other words, a value of 2400 can be use as the divisor. This makes a value of 1 for dx,dy adequate for regional plots and a value of just larger than 2 adequate for the continental US. This is a rough computation because different projections will yield slightly different domain sizes. Finally, adjust the aspect ratio of the plot by changing the nx,ny parameters. These may not need to be changed unless the domain is square or oblong.  Here are some examples:

39,-97,2.3 United States
id:KORD,.5 Small region centered over Chicago
ll,0,0,37,19,10 The whole globe on a lat-lon projection
ps,90,-90,8 Northern hemisphere
sat:0:-75,34.95,-82.95,640,427,0.108,0.095 Satellite image projection.  The satellite is centered over 75W and the image is centered at 34.95,-82.95.  The nx,ny specify the image size which is 640x427.  The dx,dy specify the distance between pixels in projection coordinates. In most satellite image cases, these values will not be equal.

Selecting a Domain for a non-Map Projection

In selecting a plot domain, first determine the coordinate of the lower left coordinate of the domain and that will be clat and clon. For simplicity, X is latitude and Y is longitude in this specification. Next determine the rough size of the domain to capture all the data of interest. The X distance is dx and the Y dy. Finally, adjust the aspect ratio of the plot by changing the nx,ny parameters. Remember 2,2 is the smallest possible value here.

xy,-10,0,20,10 XY plot ranging from -10 to 10 in X and 0 to 10 in Y
cat,0,0,10,75 Category plot, plotting first 11 items with a Y range of 0 to 75

For further information about WXP, email technical-support@weather.unisys.com
Last updated by Dan Vietor on Mar 5, 1998