具有最小刻度的图表的尼斯标签算法

Question

我需要手动计算Ticklabels和Tickrange for charts.

我知道好标记的"标准"算法(参见http://books.google.de/books?id=fvA7zLEFWZgC&pg=PA61&lpg=PA61&redir_esc=y#v=onepage&q&f=false),我也知道这个Java实现.

问题是,使用这种算法,滴答声"太聪明"了.这意味着,该算法决定应显示多少刻度.我的要求是,总有5个Ticks,但这些当然应该是"漂亮的".天真的方法是获得最大值,除以5并乘以ticknumber.这里的值 - 当然 - 不是最优的,而且滴答非常难看.

有没有人知道问题的解决方案或有正式算法描述的提示？

Answer 1

我是" 图表轴上的最佳缩放算法 "的作者.它曾经托管在trollop.org上,但我最近移动了域名/博客引擎.无论如何,我会在这里发布内容以便于访问.

我一直在为一项任务安排一个Android图表应用程序,并且在以精确缩放的格式呈现图表时遇到了一些问题.我花了一些时间尝试自己创建这个算法并且非常接近,但最后我在Andrew S.Glassner的一本名为"Graphics Gems,Volume 1"的书中找到了一个伪代码示例.有关问题的优秀描述在" 图形标签的良好数字 "一章中给出:

在通过计算机创建图形时,最好用"漂亮"数字标记x和y轴:简单的十进制数.例如,如果数据范围是105到543,我们可能想要绘制范围从100到600并且每100个单位放置刻度线.或者,如果数据范围是2.04到2.16,我们可能会绘制从2.00到2.20的范围,刻度间距为0.05.人类擅长选择这样的"好"数字,但简单算法则不然.朴素的标签选择算法获取数据范围并将其划分为n个相等的间隔,但这通常会导致丑陋的刻度标签.我们在这里描述了一种生成漂亮图形标签的简单方法.

主要的观察结果是十进制中"最好的"数字是1,2和5,以及这些数字的所有十次幂.我们将仅使用这些数字作为刻度线间距,并将刻度线放置在刻度线间距的倍数处...

我使用本书中的伪代码示例在Java中创建以下类:

public class NiceScale {

  private double minPoint;
  private double maxPoint;
  private double maxTicks = 10;
  private double tickSpacing;
  private double range;
  private double niceMin;
  private double niceMax;

  /**
   * Instantiates a new instance of the NiceScale class.
   *
   * @param min the minimum data point on the axis
   * @param max the maximum data point on the axis
   */
  public NiceScale(double min, double max) {
    this.minPoint = min;
    this.maxPoint = max;
    calculate();
  }

  /**
   * Calculate and update values for tick spacing and nice
   * minimum and maximum data points on the axis.
   */
  private void calculate() {
    this.range = niceNum(maxPoint - minPoint, false);
    this.tickSpacing = niceNum(range / (maxTicks - 1), true);
    this.niceMin =
      Math.floor(minPoint / tickSpacing) * tickSpacing;
    this.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.
   *
   * @param range the data range
   * @param round whether to round the result
   * @return a "nice" number to be used for the data range
   */
  private double niceNum(double range, boolean round) {
    double exponent; /** exponent of range */
    double fraction; /** fractional part of range */
    double niceFraction; /** nice, rounded fraction */

    exponent = Math.floor(Math.log10(range));
    fraction = range / 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.
   *
   * @param minPoint the minimum data point on the axis
   * @param maxPoint the maximum data point on the axis
   */
  public void setMinMaxPoints(double minPoint, double maxPoint) {
    this.minPoint = minPoint;
    this.maxPoint = maxPoint;
    calculate();
  }

  /**
   * Sets maximum number of tick marks we're comfortable with
   *
   * @param maxTicks the maximum number of tick marks for the axis
   */
  public void setMaxTicks(double maxTicks) {
    this.maxTicks = maxTicks;
    calculate();
  }
}

然后我们可以像这样使用上面的代码:

NiceScale numScale = new NiceScale(-0.085, 0.173);

System.out.println("Tick Spacing:\t" + numScale.getTickSpacing());
System.out.println("Nice Minimum:\t" + numScale.getNiceMin());
System.out.println("Nice Maximum:\t" + numScale.getNiceMax());

然后,它将输出格式良好的数字,以便在您需要创建漂亮比例的任何应用程序中使用.= d

Tick Spacing: 0.05
Nice Minimum: -0.1
Nice Maximum: 0.2

Answer 2

这是一个javascript版本：

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();
}

请享用！

Answer 3

我已根据我的要求将上面的 java 代码转换为 Python。

 import math

  class NiceScale:
    def __init__(self, minv,maxv):
        self.maxTicks = 6
        self.tickSpacing = 0
        self.lst = 10
        self.niceMin = 0
        self.niceMax = 0
        self.minPoint = minv
        self.maxPoint = maxv
        self.calculate()

    def calculate(self):
        self.lst = self.niceNum(self.maxPoint - self.minPoint, False)
        self.tickSpacing = self.niceNum(self.lst / (self.maxTicks - 1), True)
        self.niceMin = math.floor(self.minPoint / self.tickSpacing) * self.tickSpacing
        self.niceMax = math.ceil(self.maxPoint / self.tickSpacing) * self.tickSpacing

    def niceNum(self, lst, rround):
        self.lst = lst
        exponent = 0 # exponent of range */
        fraction = 0 # fractional part of range */
        niceFraction = 0 # nice, rounded fraction */

        exponent = math.floor(math.log10(self.lst));
        fraction = self.lst / math.pow(10, exponent);

        if (self.lst):
            if (fraction < 1.5):
                niceFraction = 1
            elif (fraction < 3):
                niceFraction = 2
            elif (fraction < 7):
                niceFraction = 5;
            else:
                niceFraction = 10;
        else :
            if (fraction <= 1):
                niceFraction = 1
            elif (fraction <= 2):
                niceFraction = 2
            elif (fraction <= 5):
                niceFraction = 5
            else:
                niceFraction = 10

        return niceFraction * math.pow(10, exponent)

    def setMinMaxPoints(self, minPoint, maxPoint):
          self.minPoint = minPoint
          self.maxPoint = maxPoint
          self.calculate()

    def setMaxTicks(self, maxTicks):
        self.maxTicks = maxTicks;
        self.calculate()

a=NiceScale(14024, 17756)
print "a.lst ", a.lst
print "a.maxPoint ", a.maxPoint
print "a.maxTicks ", a.maxTicks
print "a.minPoint ", a.minPoint
print "a.niceMax ", a.niceMax
print "a.niceMin ", a.niceMin
print "a.tickSpacing ", a.tickSpacing

Answer 4

您应该能够通过较小的修正来使用 Java 实现。

将 maxticks 更改为 5。

将计算方法更改为：

private void calculate() {
        this.range = niceNum(maxPoint - minPoint, false);
        this.tickSpacing = niceNum(range / (maxTicks - 1), true);
        this.niceMin =
            Math.floor(minPoint / tickSpacing) * tickSpacing;
        this.niceMax = this.niceMin + tickSpacing * (maxticks - 1); // Always display maxticks
    }

免责声明：请注意，我尚未对此进行测试，因此您可能需要对其进行调整以使其看起来不错。我建议的解决方案在图表顶部添加额外的空间，以便始终为 5 个刻度腾出空间。在某些情况下这可能看起来很难看。