Nice Label Algorithm for Charts with minimum ticks

Question

I need to calculate the Ticklabels and the Tickrange for charts manually.

I know the \"standard\" algorithm for nice ticks (see http://books.google.de/books?id=fvA7

Answer 1

Here is a javascript version:

var minPoint;
var maxPoint;
var maxTicks = 10;
var tickSpacing;
var range;
var niceMin;
var niceMax;

/**
 * Instantiates a new instance of the NiceScale class.
 *
 *  min the minimum data point on the axis
 *  max the maximum data point on the axis
 */
function niceScale( min, max) {
    minPoint = min;
    maxPoint = max;
    calculate();
    return {
        tickSpacing: tickSpacing,
        niceMinimum: niceMin,
        niceMaximum: niceMax
    };
}



/**
 * Calculate and update values for tick spacing and nice
 * minimum and maximum data points on the axis.
 */
function calculate() {
    range = niceNum(maxPoint - minPoint, false);
    tickSpacing = niceNum(range / (maxTicks - 1), true);
    niceMin =
      Math.floor(minPoint / tickSpacing) * tickSpacing;
    niceMax =
      Math.ceil(maxPoint / tickSpacing) * tickSpacing;
}

/**
 * Returns a "nice" number approximately equal to range Rounds
 * the number if round = true Takes the ceiling if round = false.
 *
 *  localRange the data range
 *  round whether to round the result
 *  a "nice" number to be used for the data range
 */
function niceNum( localRange,  round) {
    var exponent; /** exponent of localRange */
    var fraction; /** fractional part of localRange */
    var niceFraction; /** nice, rounded fraction */

    exponent = Math.floor(Math.log10(localRange));
    fraction = localRange / Math.pow(10, exponent);

    if (round) {
        if (fraction < 1.5)
            niceFraction = 1;
        else if (fraction < 3)
            niceFraction = 2;
        else if (fraction < 7)
            niceFraction = 5;
        else
            niceFraction = 10;
    } else {
        if (fraction <= 1)
            niceFraction = 1;
        else if (fraction <= 2)
            niceFraction = 2;
        else if (fraction <= 5)
            niceFraction = 5;
        else
            niceFraction = 10;
    }

    return niceFraction * Math.pow(10, exponent);
}

/**
 * Sets the minimum and maximum data points for the axis.
 *
 *  minPoint the minimum data point on the axis
 *  maxPoint the maximum data point on the axis
 */
function setMinMaxPoints( localMinPoint,  localMaxPoint) {
    minPoint = localMinPoint;
    maxPoint = localMaxoint;
    calculate();
}

/**
 * Sets maximum number of tick marks we're comfortable with
 *
 *  maxTicks the maximum number of tick marks for the axis
 */
function setMaxTicks(localMaxTicks) {
    maxTicks = localMaxTicks;
    calculate();
}

Enjoy!