>
> I have just finished an HLU contour plotting program, but find the
> plots it produces confusing, and even more importantly unpublishable,
> because the HLU line labelling produces _very_ few line labels so the
> value of many of the lines is ambiguous. HLU gives no control over
> the spacing between labels on a given contour so I seem to have no way
> of fixing the problem. Perhaps someone who uses HLU contour plotting
> (does anyone?) will have a brilliant solution.
>
> These are not plots with strange or jagged contour patterns. There
> is plenty of space for the labels, given the label size and the
> spacing between differing contour lines. There is no tightly packed
> contours problem and the lines are fairly smooth. A sample plot has
> about 9 contour lines of reasonable length, many extending over the
> entire x domain - but at best I can get only 2 of the lines to be
> labelled. This is despite trying to force _every_ line to be labelled
> by setting
> cnMonoLevelFlag = True
> cnLevelFlag = LineAndLabel
>
> I have been using the default value of cnLineLabelPlacementMode, but
> setting it to "Computed" gives the same result and setting it to
> "Constant" gives 0 labelled lines, so that is not a solution.
>
> The only thing that I can think is unusual is that the grid consists
> of a large number of points in the x direction (960) and perhaps lines
> that appear relatively smooth in the displayed plot have a fine-scale
> jaggedness which confuses the line label plotting routine. But if
> that were really the problem, I wouldn't think it would produce _any_
> line labels, yet it does - just not very many.
>
Dear Dr. Glendening:
We apologize for the scarcity of documentation on this issue, but in fact
it is possible to control the density of line labels in an HLU contour plot.
First, you need to know that for the "Constant" line label placement mode, the
labels are actually rendered as part of a line dash pattern. Admittedly,
this is not obvious, particularly when you are using the default solid line
pattern. However, the consequence is that you can control the spacing between
labels by setting the line dash segment length resource, cnLineDashSegLenF.
Although there are no native HLU resources for controlling line label
placement when using the "Randomized" or "Computed" modes, there is a
currently undocumented resource that allows access to a number of otherwise
inaccessible parameters belonging to the LLU Conpack package that underlies
the HLU ContourPlot. It is a string array resource called cnConpackParams.
Here is an example of its use in a resource file:
*cnConpackParams: (/ RC1:0.05 , RC2:0.1 , RC3:0.05 , \
PC1:7.0 , PC2:20.0 , PC3:120.0 , PC4:0.01 , PC5:0.05 , PC6:0.05 , \
PW1:0.0 , PW2:0.0 , PW3:0.0 , PW4:0.0 /)
Each element of the array is a string consisting of a Conpack parameter
name and its desired value separated by the colon character. If set
in the program source you would need to quote each string. This example
includes all the parameters that affect the "Randomized" and "Computed"
placement modes, and the values set should result in the appearance of
more labels than the default settings. Look at
http://ngwww.ucar.edu/ngdoc/ng4.1/supplements/conpack/#ParameterDescriptions
for a description of each of these parameters, and at
http://ngwww.ucar.edu/ngdoc/ng4.1/supplements/conpack/#IntroPenaltyScheme
for a discussion of the algorithm and parameters used by the "Computed"
placement mode.
I should mention that the only Conpack parameters accessible using the
cnConpackParams resource are ones that are never set in the HLU code and
have been judged to have no interaction with any parameters the HLU code
does set. Here is a categorized list of the Conpack parameters that can be
set using cnConpackParams:
Contour hachuring control
HCL
HCS
HCF
High/low label density
HLX
HLY
"Computed" label placement ("Penalty scheme" in Conpack)
PC1
PC2
PC3
PC4
PC5
PC6
PW1
PW2
PW3
PW4
"Randomized" label placement ("Regular scheme" in Conpack)
RC1
RC2
RC3
Point interpolation for lines and edges
PIC
PIE
Low level workspace control parameters
IWM
RWC
RWG
RWM
cnConpackParams has not been documented as a resource because the intention
has always been to provide access to these features through the HLU
interface. However, since it may be some time before we have the chance
to implement HLU access, perhaps we should document the control that
is available. Once again, apologies for the current lack of information
on this subject.
--NCARG Talk Staff
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