Waveform cursors and "data gates"

I have a waveform graph and want to capture certain periods of the waveform. I want a cursor to appear as a line that is adjustable in length, position and level, much like data gates used in ultrasonic A-Scan applications. I have been doing this in the past by superimposing a picture drawing lines over the graph, but I think data gates using cursors would be easier to manage and simplify things. Does anyone know how to make a cursor appear as a line that can be adjusted for length and position on the graph? And it would be even better if it were adjustable with a touch screen or with the mouse.
Paul
7.1/XP
PaulG.
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind except that you happen to be insane." -- George Orwell

Paul,
There is no one, built-in function in LabVIEW that allows you to do this behavior, but you can easily code it yourself. What you have to do is detect when one of the two cursors is moved and then move the other cursor with it. If you want to also graph a line between the two cursors, you can do that, too, just by plotting it like any other plot.
Coding this behavior is a breeze in LabVIEW 8 because there is now an acutal "Cursor Move" event; I have attached a LabVIEW 8 VI that demonstrates how to implement what you are talking about. In LabVIEW 7.1 and older, this is a little more difficult because there is no "Cursor Move" event, but there is an old post that discusses possible workarounds.
Kind Regards,
E. Sulzer
Applications Engineer
National Instruments
Attachments:
CursorWindow.vi ‏22 KB

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    KIM...........kim@ aol.com.... 190121.............     2/9/2006.........2/9/2006.............928
    KIM...........kim@ aol.com.... 190132.............     2/9/2006.........2/9/2006.............928
    KIM...........kim@ aol.com.... 190133.............     2/9/2006.........2/9/2006.............928
    KIM...........kim@ aol.com.... 190159.............     2/13/2006.......2/14/2006............923
    KIM...........kim@ aol.com.... 190237.............     2/23/2006.......2/23/2006............914
    KIM...........kim@ aol.com.... 284109.............     9/28/2006.......9/28/2006............697
    KIM...........kim@ aol.com.... 286647.............     11/7/2006.......12/5/2006............629
    KIM...........kim@ aol.com.... 294631.............     4/2/2007.........3/4/2008.............174
    KIM...........kim@ aol.com.... 322922.............     7/29/2008.......7/29/2008............27
    JOE...........joe@ aol.com.... 183332.............     1/28/2004.......4/23/2004............1585
    JOE...........joe@ aol.com.... 183336.............     1/28/2004.......3/9/2004.............1630
    SAM...........sam@ aol.com....183876.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183877.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183879.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183880.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183881.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183882.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183883.............3/5/2004.........3/8/2004.............1631
    SAM...........sam@ aol.com....183884.............3/5/2004.........3/8/2004............     1631
    SAM...........sam@ aol.com....183886.............3/5/2004.........3/8/2004............     1631
    SAM...........sam@ aol.com....183887.............3/5/2004.........3/8/2004............     1631
    SAM...........sam@ aol.com....183888.............3/5/2004.........3/8/2004............     1631
    PAT...........pat@ aol.com.....291630.............2/23/2007.......7/8/2008............     48
    PAT...........pat@ aol.com.....313990.............2/27/2008.......7/28/2008............28
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    NED...........ned@ aol.com......286688.............11/8/2006.......10/3/2007............327
    NED...........ned@ aol.com.....291631.............2/23/2007.......8/21/2008............4
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    NED...........ned@ aol.com.....292410.............3/15/2007.......7/22/2008............34
    NED...........ned@ aol.com.....299410.............6/27/2007.......2/27/2008............180
    NED...........ned@ aol.com.....303790.............9/19/2007.......9/19/2007............341
    NED...........ned@ aol.com.....304268.............9/24/2007.......3/3/2008............     175
    NED...........ned@ aol.com.....308228.............12/6/2007.......12/6/2007............263
    NED...........ned@ aol.com.....316689.............3/19/2008.......3/19/2008............159
    NED...........ned@ aol.com.....316789.............3/20/2008.......3/20/2008............158
    NED...........ned@ aol.com.....317528.............3/25/2008.......3/25/2008............153
    NED...........ned@ aol.com.....321476.............6/4/2008.........6/17/2008............69
    NED...........ned@ aol.com.....322160.............7/3/2008.........8/21/2008............4
    MOE...........moe@ aol.com.....184169.............4/5/2004.......12/5/2006............629
    [email protected]/27/2004.......3/8/2004............1631
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  • Ref cursor and dynamic sql

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      select 2,1,'Scott' from dual union all
      select 2,2,'Smith' from dual union all
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             1          1 Fred
             1          2 Bloggs
             2          1 Scott
             2          2 Smith
             3          1 Jim
             3          2 Jones
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      v_v_val     varchar2(20);      -- varchar type to fetch data into
      v_d_val     date;              -- date type to fetch data into
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      v_finaltxt  varchar2(100);
      col_num     number;
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      --       that description...
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      dbms_output.put_line(chr(10)||'6,7 and 8 Fetching Data:-');
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        v_finaltxt := null;
        -- loop through each of the Projected columns
        for j in 1..col_cnt
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            -- if it's a date column
            when 12 then
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            v_finaltxt := ltrim(v_finaltxt||',"'||rpad(v_v_val,20,' ')||'"',',');
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    2 - Parsing the query
    3 - Describing the query
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    Column Name: ID                             Datatype: Number
    Column Name: RN                             Datatype: Number
    Column Name: NM                             Datatype: Varchar2
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    5 - Executing the query
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    1     ,1     ,Fred
    1     ,2     ,Bloggs
    2     ,1     ,Scott
    2     ,2     ,Smith
    3     ,1     ,Jim
    3     ,2     ,Jones
    1     ,3     ,Freddy
    1     ,4     ,Fud
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    PL/SQL procedure successfully completed.
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      3        ,max(decode(rn,2,nm)) as nm_2
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             2 Scott  Smith
             3 Jim    Jones
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      3        ,max(decode(rn,2,nm)) as nm_2
      4  from proj_test
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             1 Fred   Bloggs
             2 Scott  Smith
             3 Jim    Jones
    ... it's not giving us this 3rd entry as a new column and we can only get that by writing the expected columns into the query, but then what if more columns are added after that etc.
    If we look back at the steps of a cursor we see again that the description and projection of what columns are returned by a query happens before any data is fetched back.
    Because of this, it's not possible to have the query return back a number of columns that are based on the data itself, as no data has been fetched at the point the projection is required.
    So, what is the answer to getting an unknown number of columns in the output?
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    2) The other answer is to write dynamic SQL. Because you're not going to know the number of columns, this isn't just a simple case of building up a SQL query as a string and passing it to the EXECUTE IMMEDIATE command within PL/SQL, because you won't have a suitable structure to read the results back into as those structures must have a known number of variables for each of the columns at design time, before the data is know. As such, inside PL/SQL code, you would have to use the DBMS_SQL package, just like in the code above that showed the workings of a cursor, as the columns there are referenced by position rather than name, and you have to deal with each column seperately. What you do with each column is up to you... store them in an array/collection, process them as you get them, or whatever. They key thing though with doing this is that, just like the reporting tools, you would need to process the data first to determine what your SQL projection is, before you execute the query to fetch the data in the format you want e.g.
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      end loop;
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    Dynamic SQL Statement:-
    select id,max(decode(rn,1,nm)) as nm_1,max(decode(rn,2,nm)) as nm_2,max(decode(rn,3,nm)) as nm_3 from proj_test group by id order by id
    1 - Opening Cursor
    2 - Parsing the query
    3 - Describing the query
    3a - SQL Projection:-
    Column Name: ID                             Datatype: Number
    Column Name: NM_1                           Datatype: Varchar2
    Column Name: NM_2                           Datatype: Varchar2
    Column Name: NM_3                           Datatype: Varchar2
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    5 - Executing the query
    6,7 and 8 Fetching Data:-
    1     ,Fred                ,Bloggs              ,Freddy
    2     ,Scott               ,Smith               ,
    3     ,Jim                 ,Jones               ,
    9 - Closing the cursor
    PL/SQL procedure successfully completed.
    ... and if more data is added ...
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    2 - Parsing the query
    3 - Describing the query
    3a - SQL Projection:-
    Column Name: ID                             Datatype: Number
    Column Name: NM_1                           Datatype: Varchar2
    Column Name: NM_2                           Datatype: Varchar2
    Column Name: NM_3                           Datatype: Varchar2
    Column Name: NM_4                           Datatype: Varchar2
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    5 - Executing the query
    6,7 and 8 Fetching Data:-
    1     ,Fred                ,Bloggs              ,Freddy              ,Fud
    2     ,Scott               ,Smith               ,                    ,
    3     ,Jim                 ,Jones               ,                    ,
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    PL/SQL procedure successfully completed.
    Of course there are other methods, using dynamically generated scripts etc. (see Re: 4. How do I convert rows to columns?), but the above simply demonstrates that:-
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    b) it is not a good idea in most cases as it requires code to handle the results dynamically rather than being able to simply query directly into a known structure or variables, and
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    PL/SQL 101 : Understanding Ref Cursors
    PL/SQL 101 : Exception Handling

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