code: void setFromFractions(final double latFraction, final double lonFraction,
                            final double latFractionDelta, final double lonFractionDelta) {
          assert (lonFractionDelta >= 0.0);
          assert (latFractionDelta != 0.0);
          lonFractionMin = lonFraction;
          lonFractionMax = lonFraction + lonFractionDelta;
          if (latFractionDelta < 0) {
              latFractionMin = latFraction + 1 + latFractionDelta;    // y + yDelta can NOT be represented.
              latFractionMax = latFraction + 1;                       // y CAN be represented.
          } else {
              latFractionMin = latFraction;
              latFractionMax = latFraction + latFractionDelta;
          }
      }
docs: Generate upper and lower limits based on x and y, and delta's.