polar graph :: scatter to contour

About drawing polar contour based scatter date (radial, Angle, image_z, waves stored in table0).

In igor I convert them into matrix using <XYZtoMatrix>.

I also used origin to plot the same data. the screenshot is "polar_contour_in_origin".

My question si why the two results are different ?

In igor, interpolated results don't seem to be what I want.



first create x and y waves from your radius and angle.

Then create an empty polar graph with Igor 9.05.

From the graph menu, choose append contour, but make sure you choose the HorizCrossing and VertCrossing axes.

From the Modify Contour Appearance dialog, choose Fill Contours.

Open the Modify Polar Graph panel, switch to the range tab, and set the radius and angle ranges to match.


Thank you for your advice.

       Sorry, I didn't make myself clear.

       What I mean is why do the two programs plot differently based on same data?
       Which one should I trust?

data show

In reply to by Qianlix

Qianlix wrote:

       What I mean is why do the two programs plot differently based on same data?
       Which one should I trust?

I don't know anything about Origin, but it looks like the Origin graph has the text "Speed mode is on", which might indicate that it's downsampling your data or otherwise altering the representation of the data in order to make the drawing faster. You might try turning speed mode off before you compare the plots.

I've attached my implementation of what I think you are going for (a polar image not a contour).

After creating the interpolated image, I used the Modify Polar Graph panel's Append Image button (requires Igor 9.05) to select the created image matrix, and then adjusted the polar graph axes ranges and other settings (angle direction and angle 0 location) to match the image's angle direction and angle 0 location specified in the ImageFromPolarCoordinates macro.

See the .png attachment for the result.

For those that don't want to download the revised experiment, I implemented the following code to convert from polar to rectangular followed by ImageInterpolate:

// Argument order is arranged to make missing parameters dialog look organized.
Macro ImageFromPolarCoordinates(wRadiusName, rows, wAngleName, cols, wSpeedName, clockwiseChoice, displayImageChoice, zeroAtChoice)
    String wRadiusName="radial"
    String wAngleName="Angle"
    String wSpeedName="image_z"

    Variable rows=200, cols=200
    Variable clockwiseChoice = 2        // 1=ccw, 2=cw
    Variable zeroAtChoice = 3       // 1 = right, 2 = left, 3 = top, 4 = bottom
    Variable displayImageChoice = 1 // 1 = yes, 2 = no
    Prompt wRadiusName,"Radius Wave",popup,WaveList("*",";","DIMS:1")
    Prompt wAngleName,"Angle Wave (degrees)",popup,WaveList("*",";","DIMS:1")
    Prompt wSpeedName,"Speed wave (z)",popup,WaveList("*",";","DIMS:1")
    Prompt rows,"number of rows for matrix"
    Prompt cols,"number of columns for matrix"
    Prompt clockwiseChoice,"Angle Direction",popup, "counter-clockwise;Clockwise;"
    Prompt zeroAtChoice,"Zero at",popup, "right;left;top;bottom;"
    Prompt displayImageChoice,"Display Image in New Graph",popup, "yes;no;"

    Variable angleDir = clockwiseChoice == 1 ? 1 : -1
    Variable angle0 = 0     // right
    if( zeroAtChoice == 2 ) // left
        angle0 = 180
    if( zeroAtChoice == 3 ) // top
        angle0 = -90
    if( zeroAtChoice == 4 ) // bottom
        angle0 = +90
    String imageName = fImageFromPolarCoordinates($wRadiusName, $wAngleName, $wSpeedName, rows, cols, angleDir, angle0)

    if( displayImageChoice == 1 ) // yes
        Display/K=0;AppendImage $imageName
        ModifyGraph width={Plan,1,bottom,left}
        // Set Axes Symmetrical about zero
        SetAxis/A/E=2 left
        SetAxis/A/E=2 bottom
        ModifyImage ''#0 ctab= {*,*,Turbo,0}
        if( 0 ) // debugging
            String dir = StringFromList(clockwiseChoice-1,"counter-clockwise;Clockwise;")
            String where = StringFromList(zeroAtChoice-1,"right;left;top;bottom;")
            TextBox/C/N=choices dir +" at "+where

// returns name of image
Function/S fImageFromPolarCoordinates(radius, angle, speed, rows, cols, angleDir, angle0)
    Wave radius, angle, speed // presumed same length 1-D waves, angle in degrees
    Variable rows, cols
    Variable angleDir, angle0

    String prefix= NameOfWave(radius)+NameOfWave(angle)
    String nameX = prefix+"_polarX"
    String nameY = prefix+"_polarY"
    Duplicate/O radius, $nameX,$nameY
    WAVE wx = $nameX
    WAVE wy = $nameY

    wx = radius * cos((angleDir*angle-angle0)*pi/180)
    wy = radius * sin((angleDir*angle-angle0)*pi/180)
    // determine the X and Y bounds of the XY data
    WaveStats/M=0/Q wx
    Variable xmin= V_min, xmax = V_max
    Variable dx= (xmax-xmin) / (rows-1)
    if( dx <= 0 )
        DoAlert 0, "max X must be greater than min X!"
        return ""
    xmax += dx + dx/2   // version 6.38: ImageInterpolate computes nXPoints=floor(abs(xmax-xmin)/dx)
    WaveStats/M=0/Q wy
    Variable ymin= V_min, ymax = V_max
    Variable dy= (ymax-ymin) / (cols-1)
    if( dy <= 0 )
        DoAlert 0, "max Y must be greater than min Y!"
        return ""
    ymax += dy + dy/2
    // ImageInterpolate requires triplet wave
    String tripletName=prefix+"_temp"
    Concatenate/O/DL {wx,wy,speed},$tripletName
    WAVE wtriplet=$tripletName

    Variable outerValue=NaN // transparent outside of boundary
    Variable pftl = 1e-5        // overcome perturbation

    String imageName = prefix+"_image"
    ImageInterpolate/DEST=$imageName/PFTL=(pftl)/E=(outerValue)/S={(xmin),(dx),(xmax),(ymin),(dy),(ymax)} Voronoi, wtriplet

    KillWaves/Z wtriplet
    return imageName