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Problems with zoom and scroll for log chart


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I have a logarithmic line chart.  Logbase is 10.  The X-axis is time.  There

are about 9,000 data points in 9 series (1000 time points). Data values

range from around 0.1 to around 1800. I set the Y-axis min and max manually

and call RecalcScale().

I enabled the zoom control on the toolbar. Users see some odd behaviors

when they zoom. The user enables zoom and drags ("rubber-bands") an area.

But when the mouse is released and the chart repaints, the data selected

within the rubber band area does not appear in the displayed chart area.

Also, scrolling resolution is very poor. I tried setting the minor step to

a small value to improve scroll resolution. This works in some areas of the

chart, especially for small Y-values. But the Y-axis labels get what appear

to be rounding errors as I scroll...instead of displaying 1, 10, 100, ...

they display values like 9.985, 99.85, ... etc. And when an area near the

"top" of the chart is rubber-banded, the Y-axis sometimes paints oddly;

perhaps only one horizontal gridline will appear, and it will be close to

the X-axis. On occasions, I've seen Y-axis labels also appear out of order

(a smaller value appears closer to the top of the chart area).

I note that it's documented that you cannot set the minor step to less than

the log base. But this seems a very odd restriction...suppose I have a

dataset in which the values lie between 0.1 and 10.0, and I'm displaying

them on a log10 graph. This is a sensible thing to do, but if the minor

step is 10, doesn't that mean that vertical scrolling won't work?

I have a small standalone app to demonstrate some of this. I would post it

but it is accompanied by a 0.5MB XML file which is the data set. Should I

post such a large file?

Thanks, Jeff Berkowitz

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Actually we don't require the whole application.

Simply export the chart in question to a binary file using the Export method

and attach to your next post.

Please provide us with instructions on where to zoom and what problems do

you get when you zoom in those areas.

Do you know that you can provide you own scrolling interface ?

The Axis object provides a SetScrollView method that allows you to view any

portion of the axis you want, you may, using this function implement some

kind of "logarithmic scrolling".

--

FP

Software FX, Inc.

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Hi, thanks so much for your answer, and sorry about the delay in my

response.

I have attached the binary export and three screen shots. The first shows

my test app. When you try it, zoom to the area shown by the red box in the

upper left-hand corner, but (unlike the red box) stay above the "1000.0"

line when you zoom. The second shows what happens when I zoom. Note the

tiny vertical scroll thumb. The thumb only has two positions where it will

stop, "all the way down" and "all they way up". The effect of moving the

thumb "all the way up" is shown in the third screen shot. Now you can see

the upper data series, but the Y-axis label is garbled. If you resize the

window then the label paints correctly.

I will experiment with the SetScrollView method and see what I can come up

with.

Jeff

"Software FX Support" <support@softwarefx.com> wrote in message

news:w4R4GA3ZEHA.3080@webserver3.softwarefx.com...

> Actually we don't require the whole application.

>

> Simply export the chart in question to a binary file using the Export

method

> and attach to your next post.

>

> Please provide us with instructions on where to zoom and what problems do

> you get when you zoom in those areas.

>

> Do you know that you can provide you own scrolling interface ?

>

> The Axis object provides a SetScrollView method that allows you to view

any

> portion of the axis you want, you may, using this function implement some

> kind of "logarithmic scrolling".

>

> --

> FP

> Software FX, Inc.

>

>

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  • 2 weeks later...

Sorry again for the delay in answering.

That's awesome. Thanks. You guys are really on the ball in this support

group.

Jeff Berkowitz

"SoftwareFX Support" <noreply@softwarefx.com> wrote in message

news:lWFr3BebEHA.3152@webserver3.softwarefx.com...

> Thank you.

>

> Thanks to your sample I was able to identify the problem. I found it.

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