[Xastir] Ellipse Area Objects

[Lynn W. Deffenbaugh (Mr)]

Greetings to the xastir developers,

As some of you might remember, I've been working to implement area 
objects in APRSISCE/32 and received some valuable example test files and 
screen shots of what they're supposed to look like (see link below) from 
Curt.  However, it was noted that Bob had not yet documented what 
ellipses are supposed to look like, so I skipped them for a while (and 
made them look like boxes just to be different).

Well, tonight I decided to just implement them as an elliptical shape 
inside of what would have been the box shape.  This means that they can 
be wide or tall, but not angled from the baseline because there's 
nothing in the area object spec to accomplish that.

I though you all might like to know so that maybe at least two APRS 
clients will render them the same.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

PS.   To keep circles round, I average the x and y offsets and use that 
as the radius.  The code I use to do that along with my ellipse code are 
below if anyone finds it useful.

xastir's rendering: http://wetnet.net/~we7u/example_objects3.png

APRSISCE/32's: http://tinyurl.com/APRSIS32-examples3

Tyy/Cxx where yOff is yy*yy/1500 and xOff is xx*xx/1500
APRS->lat/lon are the object's actual location.
I purposely make rough-stepped circles (20 degrees) for performance on 
Windows Mobile

     case 5: // Color-filled circle
         ml->Filled = TRUE;
     case 0: // Open Circle
     {    double a, radius = (xOff+yOff)/2;
         double step = 20;
         int p;
         Closed = TRUE;
         ml->Count = (int)((360.0/step)+1);
         ml->Points = (MULTILINE_POINT_S 
*)malloc(sizeof(*ml->Points)*(ml->Count+1));    /* +1 for possible 
closure */
         for (p=0, a=0; a<360+step; p++, a+=step)
         {    ml->Points[p].Lat = APRS->lat - radius * sin(DegToRad(a));
             ml->Points[p].Lon = APRS->lon + radius * cos(DegToRad(a));
         }
         break;
     }
     case 7: // Color-filled ellipse
         ml->Filled = TRUE;
     case 2: // Open ellipse
     {    double t;
         double step = 20;
         int p;
         Closed = TRUE;
         ml->Count = (int)((360.0/step)+1);
         ml->Points = (MULTILINE_POINT_S 
*)malloc(sizeof(*ml->Points)*(ml->Count+1));    /* +1 for possible 
closure */
         for (p=0, t=0; t<360+step; p++, t+=step)
         {    double rads = DegToRad(t);
             if (yOff > xOff)
             {    ml->Points[p].Lat = APRS->lat + yOff*sin(rads);
                 ml->Points[p].Lon = APRS->lon + xOff*cos(rads);
             } else
             {    ml->Points[p].Lat = APRS->lat + yOff*cos(rads);
                 ml->Points[p].Lon = APRS->lon + xOff*sin(rads);
             }
         }
         break;
     }