Problem with Surface plot

[Peter]

I have a problem with 3D surface display.
My application is a Win32 program . The surface is defined as a 2D matrix with the size of Hcell-by-Vcell The surface height is defined as the value of the matrix elements, the x and y coordinates as the indecies of the matrix elements.
The matrix is stored in a double precision linear array Surf3d with the size of (Hcell+1)*(Vcell+1)
The surface values are arranged in the linear array as:

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					for (r=0;r<Vcell;r++) { // rows
						for (c=0;c<Hcell;c++) { // columns
							i = r*Hcell + c;
							Surf3d[i] = (double)rec[i];
						}
					}

rec are the experimentally measured surface data.
When I save the Surf3d array and display in Excel using Excel's native surface plot I see a completely acceptable surface.

I my program I try to display using

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                /* Initialize DPLOT structure to 0's: */
                memset(&DPlot,0,sizeof(DPlot));

                /* Fill in members of DPLOT structure */
                DPlot.Version    = DPLOT_DDE_VERSION;
                DPlot.hwnd       = (DWORD)hDlg;
                DPlot.DataFormat  = DATA_3D;
                DPlot.MaxCurves  = Hcell;
                DPlot.MaxPoints  = Vcell;
                DPlot.NumCurves  = 1;
                DPlot.Scale      = SCALE_LINEARX_LINEARY;
                strcpy(DPlot.Title[0],"The surface");
                strcpy(DPlot.XAxis,"X");
                strcpy(DPlot.YAxis,"Y");

                Lighting = 0;
                GetDlgItemText(hDlg,IDC_XRANGEEDIT,szText,sizeof(szText));
                xhi = atof(szText);
                GetDlgItemText(hDlg,IDC_YRANGEEDIT,szText,sizeof(szText));
                yhi = atof(szText);
                GetDlgItemText(hDlg,IDC_ZLORANGEEDIT,szText,sizeof(szText));
                zlo = atof(szText);
                GetDlgItemText(hDlg,IDC_ZHIRANGEEDIT,szText,sizeof(szText));
                zhi = atof(szText);
                xlo = 0.0; ylo=0.0;

                //if(Is3DView)
                sprintf_s(szExec, 1024,"[Caption(\"Heatbump plot\")]"
                          "[Contour3D(1)][ContourView(%d,20)][ContourLighting(%d,0.05)]", (int)angle, Lighting);

                sprintf_s(line, 1000, "[ContourGrid(0)][ContourAxes(1)][ContourMethod(0)][ContourLevels(20,%.3f, %.3f)]"
                          "[ContourScales(1,1,%d)][ManualScale(0,0,%.3f, %.3f,%.3f,%.3f)]"
                          "[FontPoints(1,8)][FontPoints(2,12)][FontPoints(3,12)]"
                          "[FontPoints(4,10)][FontPoints(5,10)][FontPoints(6,8)][FontPoints(8,10)]"
                          "[ZAxisLabel(\"Height\")][DocMaximize()]", MinRec, MaxRec, 5, xhi, yhi, zlo, zhi);

                strcat(szExec, line);


                if (hbmp) {
                    DeleteObject(hbmp);
                    hbmp = 0;
                }
                if (DocNum) dPlot_Command(DocNum, "[FileClose()]");
				DocNum = dPlot_Plot8(&DPlot, extents, Surf3d, szExec);
                if (DocNum) {
                    SetBitmapToFrame();
                    Is3D = 1;
                }
                free(z);

The Surface shown by dplot is very different from what I see from the Excel display:
The surface I am supposed to see in dplot is an inclined plane (as it show up in Excel surface plot) but with the dplot it looks like a plane surface with a warp aling the (i,i) line.

Any idea what could cause this defect?
Peter

[Peter]

I wanted to attach a word doc with the two plots - I don't know how....
Peter

[DPlotAdmin]

No attachments here, sorry. You're welcome to send files to support@dplot.com if you think it is necessary after this.

It looks to me like your loop limits and the calculation of i aren't correct, should be:

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for (r=0;r<Vcell+1;r++) { // rows 
    for (c=0;c<Hcell+1;c++) { // columns 
        i = r*(Hcell+1) + c; 
        Surf3d[i] = (double)rec[i]; 
    } 
} 

[Peter]

No attachments here, sorry. You're welcome to send files to support@dplot.com if you think it is necessary after this.

It looks to me like your loop limits and the calculation of i aren't correct, should be:

Code: Select all

for (r=0;r<Vcell+1;r++) { // rows 
    for (c=0;c<Hcell+1;c++) { // columns 
        i = r*(Hcell+1) + c; 
        Surf3d[i] = (double)rec[i]; 
    } 
} 

David, I don't quite get it:
The double-loop in your code snippet implies that the array has a dimension of Hcell+1 by Vcell+1.
In reality there are Hcell elements horizonally and Vcell elements vertically.
Peter

[DPlotAdmin]

OK, in that case this:

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DPlot.MaxCurves  = Hcell;
DPlot.MaxPoints  = Vcell; 

should be

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DPlot.MaxCurves  = Hcell-1;
DPlot.MaxPoints  = Vcell-1; 

And I probably need to do a better job of explaining this in the example source. Those are the number of rectangular grid cells in each direction (1 less than the number of points).