TGaxis*¶
继承 TLine, TAttText
Service class for the graphical representation of axis.
Instances of this class are generated by the histograms and graphs painting classes when TAxis are drawn. TGaxis is the “painter class”of TAxis. Therefore it is mainly used via TAxis` even if is some occasion it can be used directly to draw an axis which is not part of a graph or an instance. For instance to draw an extra scale on a plot.
Basic definition
Definition with a function
Logarithmic axis
Blank axis
Tick marks’ orientation
Tick marks’ size
Labels’ positionning
Labels’ orientation
Labels’ position on tick marks
Labels’ format
Alphanumeric labels
Number of divisions optimisation
Maximum Number of Digits for the axis labels
Optional grid
Time axis
Logarithmic axis¶
By default axis are linear. To define a TGaxis as logarithmic, it is enough to create it with the option “G”.
When plotting an histogram or a graph the logarithmic scale can be set using:
gPad->SetLogx(1); set the logarithmic scale on the X axis
gPad->SetLogy(1); set the logarithmic scale on the Y axis
When the SetMoreLogLabels() method is called more labels are drawn when in logarithmic scale and there is a small number of decades (less than 3).
Tick marks’ orientation¶
By default tick marks are drawn on the positive side of the axis, except for vertical axis for which the default is negative. The chop parameter allows to control the tick marks orientation:
chopt = “+”: tick marks are drawn on Positive side. (default)
chopt =”-“: tick mark are drawn on the negative side.
chopt = “+-“: tick marks are drawn on both sides of the axis.
chopt = “U”: Unlabelled axis, default is labeled.
Tick marks’ size¶
By default, tick marks have a length equal to 3 per cent of the axis length. When the option “S” is specified, the length of the tick marks is equal to fTickSize*axis_length, where fTickSize may be set via TGaxis::SetTickSize.
When plotting an histogram h the tick marks size can be changed using:
h->GetXaxis()->SetTickLength(0.02); set the tick length for the X axis
gStyle->SetTickLength(0.02,”x”); set the tick length for the X axis of all histograms drawn after this instruction.
A good way to remove tick marks on an axis is to set the tick length to 0: h->GetXaxis()->SetTickLength(0.);
Labels’ positionning¶
Labels are normally drawn on side opposite to tick marks. However the option “=” allows to draw them on the same side.
Labels’ orientation¶
By default axis labels are drawn parallel to the axis. However if the axis is vertical then are drawn perpendicular to the axis.
Labels’ position on tick marks¶
By default axis labels are centered on tick marks. However, for vertical axis, they are right adjusted. The chop parameter allows to control the labels’ position on tick marks:
chopt = “R”: labels are Right adjusted on tick mark.(default is centered)
chopt = “L”: labels are Left adjusted on tick mark.
chopt = “C”: labels are Centered on tick mark.
chopt = “M”: In the Middle of the divisions.
Labels’ format¶
Blank characters are stripped, and then the label is correctly aligned. the dot, if last character of the string, is also stripped, unless the option “.” (a dot, or period) is specified. if SetDecimals(kTRUE) has been called all labels have the same number of decimals after the “.” The same is true if gStyle->SetStripDecimals(kFALSE) has been called.
In the following, we have some parameters, like tick marks length and characters height (in percentage of the length of the axis (user’s coordinates)) The default values are as follows:
Primary tick marks: 3.0 %
Secondary tick marks: 1.5 %
Third order tick marks: .75 %
Characters height for labels: 4%
Labels offset: 1.0 %
By default, an exponent of the form 10^N is used when the label values are either all very small or very large. One can disable the exponent by calling axis.SetNoExponent(kTRUE).
TGaxis::SetExponentOffset(Float_t xoff, Float_t yoff, Option_t *axis) is static function to set X and Y offset of the axis 10^n notation. It is in % of the pad size. It can be negative. axis specifies which axis (“x” or/and “y”), default is “x” if axis = “xz” set the two axes
Alphanumeric labels¶
Axis labels can be any alphanumeric character strings. Such axis can be produced only with histograms because the labels’definition is stored in TAxis.
Because the alphanumeric labels are usually longer that the numeric labels, their size is by default equal to “0.66666 * the_numeric_labels_size”.
Number of divisions optimisation¶
By default the number of divisions on axis is optimised to show a coherent labelling of the main tick marks. The number of division (ndiv) is a composite integer given by:
ndiv = N1 + 100*N2 + 10000*N3
N1 = number of 1st divisions.
N2 = number of 2nd divisions.
N3 = number of 3rd divisions.
by default the value of N1, N2 and N3 are maximum values. After optimisation the real number of divisions will be smaller or equal to these value. If one wants to bypass the optimisation, the option “N” should be given when the TGaxis is created. The option “I” also act on the number of division as it will force an integer labelling of the axis.
On an histogram pointer h the number of divisions can be set in different ways:.
Directly on the histogram. The following will set the number of division to 510 on the X axis of h. To avoid optimization the number of divisions should be negative (ie: -510);
h->SetNdivisions(510, "X");
On the axis itself:
h->GetXaxis()->SetNdivisions(510, kTRUE);
The first parameter is the number of division. If it is negative of if the second parameter is kFALSE then the number of divisions is not optimised. And other signature is also allowed:
h->GetXaxis()->SetNdivisions(10, 5, 0, kTRUE);
Maximum Number of Digits for the axis labels¶
The static function TGaxis::SetMaxDigits sets the maximum number of digits permitted for the axis labels above which the notation with 10^N is used. For example, to accept 6 digits number like 900000 on an axis call TGaxis::SetMaxDigits(6). The default value is 5. fgMaxDigits must be greater than 0.
Optional grid¶
The option “W” allows to draw a grid on the primary tick marks. In case of a log axis, the grid is only drawn for the primary tick marks if the number of secondary and tertiary divisions is 0. SetGridLength() allows to define the length of the grid.
When plotting an histogram or a graph the grid can be set ON or OFF using:
gPad->SetGridy(1); set the grid on the X axis
gPad->SetGridx(1); set the grid on the Y axis
gPad->SetGrid(1,1); set the grid on both axis.
Time axis¶
Axis labels may be considered as times, plotted in a defined time format. The format is set with SetTimeFormat(). The TGaxis minimum (wmin) and maximum (wmax) values are considered as two time values in seconds. The time axis will be spread around the time offset value (set with SetTimeOffset()). Actually it will go from “TimeOffset+wmin” to “TimeOffset+wmax”
Usually time axis are created automatically via histograms, but one may also want to draw a time axis outside an “histogram context”. This can be done thanks to the option “T” of TGaxis.
class¶
TGaxis();
TGaxis(Double_t xmin,Double_t ymin,Double_t xmax,Double_t ymax,
Double_t wmin,Double_t wmax,Int_t ndiv=510, Option_t *chopt="",
Double_t gridlength = 0);
// Where:
// - xmin : X origin coordinate in user's coordinates space.
// - xmax : X end axis coordinate in user's coordinates space.
// - ymin : Y origin coordinate in user's coordinates space.
// - ymax : Y end axis coordinate in user's coordinates space.
// - wmin : Lowest value for the tick mark labels written on the axis.
// - wmax : Highest value for the tick mark labels written on the axis.
// - ndiv : Number of divisions.
// - ndiv=N1 + 100*N2 + 10000*N3
// - N1=number of 1st divisions.
// - N2=number of 2nd divisions.
// - N3=number of 3rd divisions. e.g.:
// - ndiv=0 --> no tick marks.
// - ndiv=2 --> 2 divisions, one tick mark in the middle of the axis.
// - chopt : Drawing options (see below).
// - gridlength: grid length on main tick marks.
TGaxis(Double_t xmin,Double_t ymin,Double_t xmax,Double_t ymax,
const char *funcname, Int_t ndiv=510, Option_t *chopt="",
Double_t gridlength = 0);
virtual ~TGaxis();
virtual void AdjustBinSize(Double_t A1, Double_t A2, Int_t nold
,Double_t &BinLow, Double_t &BinHigh, Int_t &nbins, Double_t &BinWidth);
/// Internal method for axis labels optimisation. This method adjusts the bining
/// of the axis in order to have integer values for the labels.
/// \param[in] A1,A2 Old WMIN,WMAX
/// \param[out] binLow,binHigh New WMIN,WMAX
/// \param[in] nold Old NDIV (primary divisions)
/// \param[out] nbins New NDIV
/// \param[out] binWidth Bin width
virtual void CenterLabels(Bool_t center=kTRUE);
/// If center = kTRUE axis labels are centered in the center of the bin.
/// The default is to center on the primary tick marks.
/// This option does not make sense if there are more bins than tick marks.
virtual void CenterTitle(Bool_t center=kTRUE);/// If center = kTRUE axis title will be centered. The default is right adjusted.
virtual void DrawAxis(Double_t xmin,Double_t ymin,Double_t xmax,Double_t ymax,
Double_t wmin,Double_t wmax,Int_t ndiv=510, Option_t *chopt="",
Double_t gridlength = 0);/// Draw this axis with new attributes.
Float_t GetGridLength() const {return fGridLength;}
TF1 *GetFunction() const {return fFunction;}
Int_t GetLabelColor() const {return fLabelColor;}
Int_t GetLabelFont() const {return fLabelFont;}
Float_t GetLabelOffset() const {return fLabelOffset;}
Float_t GetLabelSize() const {return fLabelSize;}
Float_t GetTitleOffset() const {return fTitleOffset;}
Float_t GetTitleSize() const {return fTitleSize;}
virtual const char *GetName() const {return fName.Data();}
virtual const char *GetOption() const {return fChopt.Data();}
virtual const char *GetTitle() const {return fTitle.Data();}
static Int_t GetMaxDigits();/// Static function returning fgMaxDigits (See SetMaxDigits).
Int_t GetNdiv() const {return fNdiv;}
Double_t GetWmin() const {return fWmin;}
Double_t GetWmax() const {return fWmax;}
Float_t GetTickSize() const {return fTickSize;}
virtual void ImportAxisAttributes(TAxis *axis);/// Internal method to import TAxis attributes to this TGaxis.
void LabelsLimits(const char *label, Int_t &first, Int_t &last);/// Internal method to find first and last character of a label.
virtual void Paint(Option_t *chopt="");/// Draw this axis with its current attributes.
virtual void PaintAxis(Double_t xmin,Double_t ymin,Double_t xmax,Double_t ymax,
Double_t &wmin,Double_t &wmax,Int_t &ndiv, Option_t *chopt="",
Double_t gridlength = 0, Bool_t drawGridOnly = kFALSE);/// Control function to draw an axis.
virtual void Rotate(Double_t X, Double_t Y, Double_t CFI, Double_t SFI
,Double_t XT, Double_t YT, Double_t &U, Double_t &V);/// Internal method to rotate axis coordinates.
virtual void SavePrimitive(std::ostream &out, Option_t *option = "");/// Save primitive as a C++ statement(s) on output stream out
void SetFunction(const char *funcname="");/// Specify a function to map the axis values.
void SetOption(Option_t *option="");/// To set axis options.
void SetLabelColor(Int_t labelcolor) {fLabelColor = labelcolor;} // *MENU*
void SetLabelFont(Int_t labelfont) {fLabelFont = labelfont;} // *MENU*
void SetLabelOffset(Float_t labeloffset) {fLabelOffset = labeloffset;} // *MENU*
void SetLabelSize(Float_t labelsize) {fLabelSize = labelsize;} // *MENU*
static void SetMaxDigits(Int_t maxd=5);
/// Static function to set `fgMaxDigits` for axis.`fgMaxDigits` is
/// the maximum number of digits permitted for the axis labels above which the
/// notation with 10^N is used.For example, to accept 6 digits number like 900000
/// on an axis call `TGaxis::SetMaxDigits(6)`. The default value is 5.
/// `fgMaxDigits` must be greater than 0.
virtual void SetName(const char *name); // *MENU* /// Change the name of the axis.
virtual void SetNdivisions(Int_t ndiv) {fNdiv = ndiv;} // *MENU*
virtual void SetMoreLogLabels(Bool_t more=kTRUE); // *MENU*
/// Set the kMoreLogLabels bit flag. When this option is selected more labels are
/// drawn when in logarithmic scale and there is a small number of decades (less than 3).
/// Note that this option is automatically inherited from TAxis
virtual void SetNoExponent(Bool_t noExponent=kTRUE); // *MENU*
/// Set the NoExponent flag. By default, an exponent of the form 10^N is used
/// when the label values are either all very small or very large. One can disable
/// the exponent by calling axis.SetNoExponent(kTRUE).
virtual void SetDecimals(Bool_t dot=kTRUE); // *MENU*
/// Set the decimals flag. By default, blank characters are stripped, and then the
/// label is correctly aligned. The dot, if last character of the string, is also
/// stripped, unless this option is specified. One can disable the option by
/// calling `axis.SetDecimals(kTRUE)`.
/// Note the bit is set in fBits (as opposed to fBits2 in TAxis!)
void SetTickSize(Float_t ticksize) {fTickSize = ticksize;} // *MENU*
void SetTickLength(Float_t ticklength) {SetTickSize(ticklength);}
void SetGridLength(Float_t gridlength) {fGridLength = gridlength;}
void SetTimeFormat(const char *tformat);
/// Change the format used for time plotting.
/// The format string for date and time use the same options as the one used
/// in the standard strftime C function, i.e. :
/// for date :
/// - `%a` abbreviated weekday name
/// - `%b` abbreviated month name
/// - `%d` day of the month (01-31)
/// - `%m` month (01-12)
/// - `%y` year without century
/// for time :
/// - `%H` hour (24-hour clock)
/// - `%I` hour (12-hour clock)
/// - `%p` local equivalent of AM or PM
/// - `%M` minute (00-59)
/// - `%S` seconds (00-61)
/// - `%%` %
void SetTimeOffset(Double_t toffset, Option_t *option="local");
virtual void SetTitle(const char *title=""); // *MENU* /// Change the title of the axis.
void SetTitleOffset(Float_t titleoffset=1) {fTitleOffset = titleoffset;} // *MENU*
/// Change the time offset. If option = "gmt", set display mode to GMT.
void SetTitleSize(Float_t titlesize) {fTitleSize = titlesize;} // *MENU*
void SetTitleFont(Int_t titlefont) {SetTextFont(titlefont);} // *MENU*
void SetTitleColor(Int_t titlecolor) {SetTextColor(titlecolor);} // *MENU*
void SetWmin(Double_t wmin) {fWmin = wmin;}
void SetWmax(Double_t wmax) {fWmax = wmax;}
static void SetExponentOffset(Float_t xoff=0., Float_t yoff=0., Option_t *axis="xy");
/// Static function to set X and Y offset of the axis 10^n notation.
/// It is in % of the pad size. It can be negative.
/// axis specifies which axis ("x","y"), default = "x"
/// if axis="xz" set the two axes
code¶
// Instead of the wmin,wmax arguments of the normal definition, the
// name of a TF1 function can be specified. This function will be used to
// map the user coordinates to the axis values and ticks.
TCanvas *c2 = new TCanvas("c2","c2",10,10,700,500);
gStyle->SetOptStat(0);
TH2F *h2 = new TH2F("h","Axes",100,0,10,100,-2,2);
h2->Draw();
TF1 *f1=new TF1("f1","-x",-10,10);
TGaxis *A1 = new TGaxis(0,2,10,2,"f1",510,"-");
A1->SetTitle("axis with decreasing values");
A1->Draw();
TF1 *f2=new TF1("f2","exp(x)",0,2);
TGaxis *A2 = new TGaxis(1,1,9,1,"f2");
A2->SetTitle("exponential axis");
A2->SetLabelSize(0.03);
A2->SetTitleSize(0.03);
A2->SetTitleOffset(1.2);
A2->Draw();
TF1 *f3=new TF1("f3","log10(x)",1,1000);
TGaxis *A3 = new TGaxis(2,-2,2,0,"f3",505,"G");
A3->SetTitle("logarithmic axis");
A3->SetLabelSize(0.03);
A3->SetTitleSize(0.03);
A3->SetTitleOffset(1.2);
A3->Draw();
return c2;
c1 = new TCanvas("c1","Examples of TGaxis",10,10,700,100);
c1->Range(-10,-1,10,1);
TGaxis *axis = new TGaxis(-8,0.,8,0.,-100000,150000,2405,"tS");
axis->SetLabelSize(0.3);
axis->SetTickSize(0.2);
TDatime da(2003,02,28,12,00,00);
axis->SetTimeOffset(da.Convert());
axis->SetTimeFormat("%d-%m-%Y");
axis->Draw();
return c1;
example¶
// The example below generates various kind of axis.
TCanvas *c1 = new TCanvas("c1","Examples of TGaxis",10,10,700,500);
c1->Range(-10,-1,10,1);
TGaxis *axis1 = new TGaxis(-4.5,-0.2,5.5,-0.2,-6,8,510,"");
axis1->SetName("axis1");
axis1->Draw();
TGaxis *axis2 = new TGaxis(-4.5,0.2,5.5,0.2,0.001,10000,510,"G");
axis2->SetName("axis2");
axis2->Draw();
TGaxis *axis3 = new TGaxis(-9,-0.8,-9,0.8,-8,8,50510,"");
axis3->SetName("axis3");
axis3->Draw();
TGaxis *axis4 = new TGaxis(-7,-0.8,-7,0.8,1,10000,50510,"G");
axis4->SetName("axis4");
axis4->Draw();
TGaxis *axis5 = new TGaxis(-4.5,-0.6,5.5,-0.6,1.2,1.32,80506,"-+");
axis5->SetName("axis5");
axis5->SetLabelSize(0.03);
axis5->SetTextFont(72);
axis5->SetLabelOffset(0.025);
axis5->Draw();
TGaxis *axis6 = new TGaxis(-4.5,0.6,5.5,0.6,100,900,50510,"-");
axis6->SetName("axis6");
axis6->Draw();
TGaxis *axis7 = new TGaxis(8,-0.8,8,0.8,0,9000,50510,"+L");
axis7->SetName("axis7");
axis7->SetLabelOffset(0.01);
axis7->Draw();
//one can make axis going top->bottom. However because of a long standing
//problem, the two x values should not be equal
TGaxis *axis8 = new TGaxis(6.5,0.8,6.499,-0.8,0,90,50510,"-");
axis8->SetName("axis8");
axis8->Draw();
return c1;