Labeling Points on a 2-D graph

Paul G. Tratnyek tratnyek at ese.ogi.edu
Fri Oct 11 12:19:14 EST 1996


> Is anyone aware of a program (preferably freeware or shareware)
> which will allow you to label the points of a 2-D graph?

The original post may have been about a more challenging question, than
what most of the replies seemed to be dealing with. For example, where you
plot height vs weight for 200 people and you want to label each point with
the persons name, so you can easilly track outliers.

I just submitted a paper that contains a lot of this type of thing. We were
plotting rate constants for a chemical reaction (x) for a dozen different
chemicals (y, category variable), and we wanted to label each point with
the reference from which the value came. We also tried "labelled" the
points with the value of some third variable like initial concentration of
the chemical reactant.

One does NOT want to be adding this information in a drawing program, and
best not in the drawing mode in a plotting program either. Usually when you
do see plots like the the ones I described above they were done in one of
the very large full-featured (main frame) statistics programs like SAS, S,
etc.

However, the with the last major release of Igor Pro (Version 3), you can
do most of these pseudo 3D data analysis plots very nicely, and still have
all the other advantages Igor offers. (number crunching, programming,
graphics control, etc.).

Basically, what Igor does is allow you to mark the points of a set of xy
data pairs with markers that reflect a third variable. That variable can be
a column of text data, or it can reflect a numberical variable in terms of
things like marker color, size, etc. You can assign a exotic font and mark
you points with special (or goofy) characters of your choice.

The only serious limitation I have found so far, is that you can't move
these markers individually. So, if there are lots of data, there's no way
to move the labels out of each other's way. To do this, I go back to what
we did before Igor Pro 3.0, which was to run a macro that creates a tag to
go with each point. The tag is a graphic object assigned to the coordinates
of each point individually. Then you can just drag them around till the
look nice and don't interfere with one another. Igor remembers the offset
and applies it if you should ever rescale the plot.

Needless to say, Igor is not freeware or shareware, but you get what you
pay for...   P. Tratnyek, Oregon Graduate Institute



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