distance calculations in s.surf.idw

[Chris Skelly]

Hi out there,
I have two questions today...

1. Is there a FAQ (frequently asked questions) or FEP (frequently encountered
   problems) list for grassp?

2. The following segment of code is from s.surf.idw main() and is used to
   calculate the distance between points so that weights for interpolation
   can be calculated based on the distance between them...

              /* fill list with first nsearch points */
          for (i = 0; i < nsearch ; i++)
          {
              dy = points[i].north - north;
              dx = points[i].east  - east;
              list[i].dist = dy*dy + dx*dx;
              list[i].z = points[i].z;
          }
              /* find the maximum distance */
          maxdist = list[max=0].dist;
          for (n = 1; n < nsearch; n++)
          {
              if (maxdist < list[n].dist)
                  maxdist = list[max=n].dist;
          }
              /* go thru rest of the points now */
          for ( ; i < npoints; i++)
          {
              dy = points[i].north - north;
              dx = points[i].east  - east;
              dist = dy*dy + dx*dx;

              if (dist < maxdist)
              {
                      /* replace the largest dist */
                  list[max].z = points[i].z;
                    list[max].dist = dist;
                    maxdist = list[max=0].dist;
                    for (n = 1; n < nsearch; n++)
                    {
                        if (maxdist < list[n].dist)
                            maxdist = list[max=n].dist;
                    }
                }
            }

    My question here:  how does this work in the latitude longitude 
    system, where you really need some spherical geometry to calculate
    distance?

    thinking i've missed something (as usual) in Oz

    chris



-- 
|\/\/\/|                             Chris Skelly
|      |                             School of Earth Sciences 
|      |   High expolsives and       Macquarie University  
|  (o)(o)   school do NOT mix.       North Ryde, 2109, NSW, OZ 
C       _)                           Tel: 612-805-8433 
 |  ,___|                            Fax: 612-805-8428 
 |    /  chris at mqclimat.cic.mq.edu.au