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Ian11-Visitor
1-Visitor
March 31, 2010
Question

Irregular grids

  • March 31, 2010
  • 4 replies
  • 9927 views
Not sure if this is the right forum - but

I have a set of data from thermocouple positions and I want to poduce a contour plot. The thermocouples were are not in a regular grid. In effect they are on a 20x30 grid, but only 20 nodes are used.

To produce a contour plot I need a regular grid that is filled - so my question is about 2d interpolation from a sparsely populated grid

any ideas ????

4 replies

P
ptc-13682881-Visitor
1-Visitor
March 31, 2010
On 3/31/2010 9:25:01 AM, ianjohnston wrote:
>Not sure if this is the right
>forum - but
>
>I have a set of data from
>thermocouple positions and I
>want to produce a contour plot.
>The thermocouples were are not
>in a regular grid. In effect
>they are on a 20x30 grid, but
>only 20 nodes are used.
>
>To produce a contour plot I
>need a regular grid that is
>filled - so my question is
>about 2d interpolation from a
>sparsely populated grid
>
>any ideas ????
______________________________

Just attach the data grid from a data file Mathcad can read or make one in your version. If you have Mathcad 14, "Save as" 11 for + collab to read.

It sounds an RHSMD contour plot.

jmG
P
ptc-13682881-Visitor
1-Visitor
March 31, 2010
It sounds an RHSMD contour plot.
rather RHMSD
R
RichardJ19-Tanzanite
19-Tanzanite
April 2, 2010
You only have data for 20 points on a 600 point grid? I don't think the right approach is likely to be interpolation. I don't think the resulting contour plot would mean much. Do you have any kind of theoretical equation that should represent the data? If you do, the best approach would be to least squares fit that to the data.

Richard
P
ptc-13682881-Visitor
1-Visitor
April 4, 2010
On 4/2/2010 10:43:14 AM, rijackson wrote:
>You only have data for 20
>points on a 600 point grid? I
>don't think the right approach
>is likely to be interpolation.
>I don't think the resulting
>contour plot would mean much.
>Do you have any kind of
>theoretical equation that
>should represent the data? If
>you do, the best approach
>would be to least squares fit
>that to the data.
>
>Richard
_______________________

>In effect they are on a 20x30 grid, but only 20 nodes are used.<<br> ___________________

I read this way:

a 20 x 30 rectangular matrix of which 20 columns out of 30 are validated , therefore a complete square 20 x 20 square matrix that can be surface plot as finely meshed as desired for a complete contour plot as well as the surface plot.
The data set is needed c/w the columns that are valued.

Few minute project = done

jmG
P
ptc-13682881-Visitor
1-Visitor
April 4, 2010
On 3/31/2010 9:25:01 AM, ianjohnston wrote:
>Not sure if this is the right
>forum - but
>
>I have a set of data from
>thermocouple positions and I
>want to poduce a contour plot.
>The thermocouples were are not
>in a regular grid. In effect
>they are on a 20x30 grid, but
>only 20 nodes are used.
>
>To produce a contour plot I
>need a regular grid that is
>filled - so my question is
>about 2d interpolation from a
>sparsely populated grid
>
>any ideas ????
______________________________

I will leave this thread as you didn't provide data. Your project is not abstracted, as such I have an immediate comment: I you use ordinary grade T/C's there is several �C uncertainty between them. If you use special grade, there is less discrepancy, but nothing is true in either case. As you are mentioning a matrix of T/C's, whether a micromatrix for biological work or a matrix for geological work where the T/C' might be km apart from each other it is logical to consider that all T/C' do respond equally. Rosemount used to charge huge $ for their module to read their T/C. At the time of the Mathcad 11 DAEP, the special T/C calibration was implemented for the Mathcad users and this special linearisation technique was passed to NI [National Instrument], they were "delighted" [as they reported]. NI has that special linearisation in one or several of their input card. If you don't revisit this collab with data, you might have advantage to contact NI and explain your project to them.

The method was applied to valid T/C, i.e: J = large range, T = cryogenic ... each type in their complete range.

jmG
I
Ian11-VisitorAuthor
1-Visitor
June 25, 2010

Just returned to this thread, and realise I probably didn't make the problem clear. I didn't really want to get into a discussion about calibrating thermocouples - I was just trying to set the scene. Anyway, my thermocouples were arranged as in attached file "thermocouples 2.jpg". I interrogated the thermocouples 4 times a second for 100 seconds and have generated an animation - see attached "EC71 thermal.wmv".

In the end I filled in the missing values by interpolation and then reset all values where the interpolation became extrapolation. Might not be mathematically as rigourous as I wanted, but the results looked reasonable and the customer was happy!

Thanks for advice and I must try and look at the RHMSD in more detail .....

R
RichardJ19-Tanzanite
19-Tanzanite
June 25, 2010

The results do look reasonable. Very nice in fact.

How did you do the interpolation?

I
Ian11-VisitorAuthor
1-Visitor
June 25, 2010

Hi Richard

First I discarded the thermocouples on the left of the centre line as shown on the map I posted earlier - these were for redundancy.

Then I created a 15x16 matrix and mapped the values I knew onto the relevant positions.

Then running along each of the columns with data in, I filled in the missing values with linear interpolation - I then ran along each row and linterp(ed) the missing values again to fill the empty columns. I had to tidy-up before the first and after the last point in each line as linterp starts extrapolating and was giving silly results

Finally I generated a mirror image and stuck the arrays together to create the symetrical pattern

Obviously I then just FRAMEd through the data file to get the time steps for the animation

If anyone is interested I will tidy up the sheet and post it

Ian

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