RE: QwtPlotSpectrogram and contour text labels .... try this update.

G'day All,

Two minor updates:

* Fixed an issue with text rotation. Needed to take into account aspect
ratio between real and display coordinates.
* Added a label step variable to choose which contour lines would have
labels. i.e. all, 2nd, 3rd, 4th, etc contour interval.

Have Fun !!

Shane Hill

-----Original Message-----
From: Hill, Shane 
Sent: Wednesday, 3 September 2008 5:16 PM
To: 'List for both Qwt users and developers'
Subject: QwtPlotSpectrogram and contour text labels .... try this.
[SEC=UNCLASSIFIED]

G'day All,

(Second try for this. The first blocked by zip file. Now using a tar.gz
file.)

Uwe or Josef: Feel free to add any aspects of this code to the base
QwtPlotSpectrogram if you think it is useful.

A while back I asked the group about text labels for the
QwtPlotSpectrogram and found, while this had not been done yet, it was
something that was on the list of things to do.

I have just spent a few days looking into this and have written and
extender class to QwtPlotSpectrogram that will add contour text labels
called LabelledSpectrogram. To test it out I have modified the
QwtPlotSpectrogram example and added another contour plot over the top
of the example (i.e. two contour diagrams in the one plot; something I
need to do). The code is in early development, but I have attached it
for anyone to have a look at, use or make comment on. Included in the
code is a sample PNG file on what it should look like.

Features of LabelledSpectrogram
-------------------------------
* Contour labels may be positions based on label placement bit flags.
Any combination of the flags may be enabled. The options are:
  * N_PER_LEVEL: Display 'N' labels per contour level evenly spaced
(sort of); default is 2 per level.
  * AT_MIN_X:    Display a label at the minimum X value for each
contour.
  * AT_MAX_X:    Display a label at the maximum X value for each
contour.
  * AT_MIN_Y:    Display a label at the minimum Y value for each
contour.
  * AT_MAX_Y:    Display a label at the maximum Y value for each
contour; the default behaviour.
  * NO_LABELS:   As it says.

* Labels are rotated to follow the contour line. There are still a few
small issues with this that I'm working on; namely that consecutive
labels may sometimes flip by 180 degrees.
* Label text is back filled to put a break in the contour line, so the
label is easier to read. This does cause an issue with the solid filled
coloured spectrogram, (maybe back filling should be turned off for this
case).
* Label font attributes may be changed.
* A margin around the plot may be set to prevent labels from getting too
close to the plot edge and become unreadable.

Have Fun !!

Shane Hill

-----------------------------------------------------
Shane D. Hill (B.E. Aero. Hons.)
Science Team Leader: Aircraft Flight Dynamics, Modelling & Simulation
Aircraft Vehicles Division Defence Science & Technology Organisation
506 Lorimer St, Fishermens Bend, Vic. 3207 AUSTRALIA
Email:  Shane.Hill <at> dsto.defence.gov.au
Voice:  +61 3 9626 7811
FAX:    +61 3 9626 7705
-----------------------------------------------------

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