Modifying Series in TDBChart

[Reinhard]

Hello,

I use Teechart Pro 7.12 VCL and I have a TDBChart connected to a DB.
If I want to display the values of the DB for example in p.u. I have to divide each y-value by a certain constant.
How can I do this?

thanks + regards
Reinhard

[Narcís]

Hi Reinhard,

Sorry but I don't understand what are you trying to achieve exactly. You could try doing something like the code below after populating your series.

Code: Select all

  for i:=0 to Series1.Count-1 do
  begin
    Series1.YValue[i] := Series1.YValue[i] / MyConst;
  end;

If that's not what you are looking for please give us some more details about your requirement.

Thanks in advance.

[Reinhard]

Hi Narcis,

the fact is, that my series depend on a DataSource.
The DataSource could be a TADODataSet (SQL), so I do not have direct access to the series values after refreshing it with CheckDataSource.
I just want to apply the constant just before displaying the y-values.

Regards, Reinhard

[Pep]

Hi Reinhard,

what about using the OnBeforeDrawValues event :

Code: Select all

procedure TForm1.Series1BeforeDrawValues(Sender: TObject);
var i : integer;
begin
for i:=0 to Series1.Count do
  Series1.YValue[i] := Series1.YValue[i]  - (Series1.YValue[i] / 2);
end;

?

Another way would be to add the data values directly to your series by iterating through your Dataset by using the AddXY method. This way you will be able to add the modified data values too.

[xxxxxx]

Hi, Pep!
What you suggested is a recursive scheme.
Don't you think such approach will result in dissapearing the whole series after several iterations with, say, zoom-unzoom?

[Narcís]

Hi Alexander,

No, I don't think so if axes are set to automatic as they would automatically set their scales according to series values.

[xxxxxx]

Hi, Narcís!
I meant

Code: Select all

limit ( Series1.YValue[i]) -> 0

[Narcís]

Hi Alexander,

Yes, that's what I understood as well. However, if you divide all series points by the same ratio the ratio between them will be preserved too. So, if instead of being from 0 to 100 it's from 0 to 0.0001, axes will be automatically scaled to represent this.

Moreover, if Reinhard only wants this to happen the very first time the series are plotted then he could use a boolean flag to determine whether this code should be executed or not.

[xxxxxx]

Hi Alexander,

Yes, that's what I understood as well. However, if you divide all series points by the same ratio the ratio between them will be preserved too. So, if instead of being from 0 to 100 it's from 0 to 0.0001, axes will be automatically scaled to represent this.

Moreover, if Reinhard only wants this to happen the very first time the series are plotted then he could use a boolean flag to determine whether this code should be executed or not.

Thanks Narcis, I appreciate your valuable comments.
In't it possible to use OnAfterAdd event for scaling Series?

[Narcís]

Hi Alexander,

OnAfterAdd event doesn't work, you could do that in the chart's OnAfterDraw event, for example:

Code: Select all

procedure TForm1.Chart1AfterDraw(Sender: TObject);
var i : integer;
begin
  for i:=0 to Series1.Count do
    Series1.YValue[i] := Series1.YValue[i]  - (Series1.YValue[i] / 2);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Chart1.Draw;
end;