VPP polar diagrams

[Eric W. Sponberg]

Does anyone know if Microsoft Excel can create a polar diagram, such as from VPP output? I have looked into this somewhat in the past and have not come up with an answer, other than it may be possible to create a custom VPP polar diagram in Excel's custom chart function. Has anyone ever done this, and if so, be willing to offer the instructions on how to create one?

I ask this because I have a fairly good VPP program that runs in DOS, and the output can go to a text file which can then be read into Excel. But the chart does not come through, and the DOS version of the chart does not make a very good presentation. An Excel polar diagram would be much better.

I welcome anyone's input. Thanks.

Eric

[DuncanG]

The last time I tried this (a few years ago) i couldn't do it in Excel and ended up modifying GnuPlot to get the result I wanted.

I'll dust it off and see if its still usable.

You wouldn't happen to have any IMS .off files I could use, would you? What Vpp are you using?

[tuks]

I just tried the standard "radar" chart, it looks ok, but the angle label is oddly placed. I can email the spreadsheet if it would help, it's very rough though.

Edit : Sorry, just looked a little closer and its not the label placement, the angles are all wrong.

[gggGuest]

Originally Posted by Eric W. Sponberg

Does anyone know if Microsoft Excel can create a polar diagram, such as from VPP output?
Eric

Yes, but you have to do a lot of fiddling in order to get the angles right.

[Tim B]

I believe the following GNUPLOT script will do it...

set polar
set xrange [0:180]
set grid
set xlabel 'True Wind Angle (deg)'
set ylabel ' Boat Speed (m/s)'
set title 'Boat Speed at wind speed of #x# m/s'
plot 'datafile' using 1:2 with linespoints

That should plot your data. replace 1:2 above, with your x,y columns.

GNUPLOT manual is at www.gnuplot.info/docs/gnuplot.pdf

Hope this helps,

Tim B.

[Gramp34]

You can put individual lines on a plot in Excel by leaving a blank row in the x-y data. Use an X-Y plot with lines but no points, then format the chart until it looks the way you want.

For example, the data below will draw radial lines from the origin every 30 degrees then a set of arcs. (More points will make the arcs smoother.) Since this is done in an X-Y plot, you need to convert all your polar data to x-y points for plotting.

You can use additional columns for the y value on each polar line as a different data series, then can format those lines with different colors, etc.

Hope this helps,

Tim

0.00 0.00
0.00 10.00

0.00 0.00
5.00 8.66

0.00 0.00
8.66 5.00

0.00 0.00
10.00 0.00

0.00 0.00
8.66 -5.00

0.00 0.00
5.00 -8.66

0.00 0.00
0.00 -10.00


0.00 2.00
0.68 1.88
1.29 1.53
1.73 1.00
1.97 0.35
1.97 -0.35
1.73 -1.00
1.29 -1.53
0.68 -1.88
0.00 -2.00

0.00 4.00
1.37 3.76
2.57 3.06
3.46 2.00
3.94 0.69
3.94 -0.69
3.46 -2.00
2.57 -3.06
1.37 -3.76
0.00 -4.00

0.00 6.00
2.05 5.64
3.86 4.60
5.20 3.00
5.91 1.04
5.91 -1.04
5.20 -3.00
3.86 -4.60
2.05 -5.64
0.00 -6.00

0.00 8.00
2.74 7.52
5.14 6.13
6.93 4.00
7.88 1.39
7.88 -1.39
6.93 -4.00
5.14 -6.13
2.74 -7.52
0.00 -8.00

0.00 10.00
3.42 9.40
6.43 7.66
8.66 5.00
9.85 1.74
9.85 -1.74
8.66 -5.00
6.43 -7.66
3.42 -9.40
0.00 -10.00

[MalSmith]

I have successfully used the Excel radar chart type in the past. I had to use even divisions for the angles to be plotted, even if there there was no data for any individual angle.

Mal.

[Pelle]

There are a number of free scripts for doing polar plots in excel out on the net. Just google "excel polar plot" and you will find plenty to choose from.

[DuncanG]

Here's an example from my modified Gnuplot -

[kenJ]

PCSail presents the data in a line graph rather than the polar chart. This is the data from a Pearson 36-2 I recently did. For simplicity I limit the number of vertical wind direction lines, more can be added if desired.

[Tim B]

Sorry,

The GNUplot script I posted above should have included the following lines, before "plot ..."

set angle degrees
set grid polar

There, that should do it...

Tim B.

[Eric W. Sponberg]

Gramp34, Thanks for the advice. I created the polar chart from your data, and I can see that that will work quite nicely.

Tim B, Thanks too. I checked the Gnuplot website, and that looks like some nice Freeware. They seem to have a number of different versions for running on a variety of platforms. I presume I would need to download only one file, but which is the best one for running on Windows XP? They did not make it obvious which one to select.

Eric

[Tim B]

http://dfn.dl.sourceforge.net/source...gp422win32.zip

Dependant on which project you're looking at on sourceforge it can be confusing. Anyway, that should get you going...

Tim B.

[Emece]

Originally Posted by DuncanG

Here's an example from my modified Gnuplot -

DuncanG,

Can you post you Gnuplot script?
Thanks a lot in advance

Emece

[DuncanG]

email sent