add this

float getColMax(int row){
 float colMax = -8000;
 float testNum;
 for (int i = 1; i < reader.getLastRowNum(); i++) {
   testNum = reader.getFloat(i, row);
   if (testNum > colMax){
     colMax = testNum;
   }
 }
 return colMax;
}

float getColMin(int row){
 float colMin = 8000;
 float testNum;
  for (int i = 1; i < reader.getLastRowNum(); i++) {
   testNum = reader.getFloat(i, row);
   if (testNum < colMin){
     colMin = testNum;
   }
 }
 return colMin;
}

thanks for the hint.  the only problem with this is, with many points, increasing strokeWeight tends to slow things down dramatically, and at some point (around 4), they begin looking like squares.