Re: [Plplot-general] Undistorted circles

[Robert P. <rob...@jk...>]

Alan W. Irwin wrote:
>> I tried the following, but it gives
>> me ellipses, e.g. when called in x12c.c:
[...]
>>    /* get axis ratio */
>>    plgvpw(&vpxmin, &vpxmax, &vpymin, &vpymax);
>>    ratio = (vpxmax -vpxmin) / (vpymax -vpymin);
> 
> What you appear to need is something that returns real device units 
> (whether they are in pixels, points, or mm doesn't matter since it is
>  only the ratio the determines the aspect ratio). I therefore suggest
> you try plgspa or plgpage.

Thank you - the following works for me:

    /* get ratio s.t. ellipse appears as circle */
    plgvpw(&vpxmin, &vpxmax, &vpymin, &vpymax);
    axisratio = (vpxmax -vpxmin) / (vpymax -vpymin);

    plgpage(&px, &py, &pxlen, &pylen, &pxoff, &pyoff);
    pageratio = pxlen * 1. / pylen;

    ratio = axisratio / pageratio;

-- Robert