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 the same thing in Objective C

YFRNiceScale.h

#import 

@interface YFRNiceScale : NSObject

@property (nonatomic, readonly) CGFloat minPoint;
@property (nonatomic, readonly) CGFloat maxPoint;
@property (nonatomic, readonly) CGFloat maxTicks;
@property (nonatomic, readonly) CGFloat tickSpacing;
@property (nonatomic, readonly) CGFloat range;
@property (nonatomic, readonly) CGFloat niceRange;
@property (nonatomic, readonly) CGFloat niceMin;
@property (nonatomic, readonly) CGFloat niceMax;


- (id) initWithMin: (CGFloat) min andMax: (CGFloat) max;
- (id) initWithNSMin: (NSDecimalNumber*) min andNSMax: (NSDecimalNumber*) max;

@end

YFRNiceScale.m

#import "YFRNiceScale.h"

@implementation YFRNiceScale

@synthesize minPoint = _minPoint;
@synthesize maxPoint = _maxPoint;
@synthesize maxTicks = _maxTicks;
@synthesize tickSpacing = _tickSpacing;
@synthesize range = _range;
@synthesize niceRange = _niceRange;
@synthesize niceMin = _niceMin;
@synthesize niceMax = _niceMax;

- (id)init {
    self = [super init];
    if (self) {

    }
    return self;
}

- (id) initWithMin: (CGFloat) min andMax: (CGFloat) max {

    if (self) {
        _maxTicks = 10;
        _minPoint = min;
        _maxPoint = max;
        [self calculate];
    }
    return [self init];
}

- (id) initWithNSMin: (NSDecimalNumber*) min andNSMax: (NSDecimalNumber*) max {

    if (self) {
        _maxTicks = 10;
        _minPoint = [min doubleValue];
        _maxPoint = [max doubleValue];
        [self calculate];
    }
    return [self init];
}


/**
 * Calculate and update values for tick spacing and nice minimum and maximum
 * data points on the axis.
 */

- (void) calculate {
    _range = [self niceNumRange: (_maxPoint-_minPoint) roundResult:NO];
    _tickSpacing = [self niceNumRange: (_range / (_maxTicks - 1)) roundResult:YES];
    _niceMin = floor(_minPoint / _tickSpacing) * _tickSpacing;
    _niceMax = ceil(_maxPoint / _tickSpacing) * _tickSpacing;

    _niceRange = _niceMax - _niceMin;
}


/**
 * 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
 */
- (CGFloat) niceNumRange:(CGFloat) aRange roundResult:(BOOL) round {
    CGFloat exponent;
    CGFloat fraction;
    CGFloat niceFraction;

    exponent = floor(log10(aRange));
    fraction = aRange / 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 = 2;
        } else {
            niceFraction = 10;
        }
    }

    return niceFraction * pow(10, exponent);
}

- (NSString*) description {
    return [NSString stringWithFormat:@"NiceScale [minPoint=%.2f, maxPoint=%.2f, maxTicks=%.2f, tickSpacing=%.2f, range=%.2f, niceMin=%.2f, niceMax=%.2f]", _minPoint, _maxPoint, _maxTicks, _tickSpacing, _range, _niceMin, _niceMax ];
}

@end

Usage:

YFRNiceScale* niceScale = [[YFRNiceScale alloc] initWithMin:0 andMax:500];
NSLog(@"Nice: %@", niceScale);