Camera and view function and properties

I've been trying to understand the view and camera functions and created the following code for illustration:

peaks(30);
ax=get(gca);
% Display values
disp('Initial values')
dispprops(ax)

% Change target
ax.CameraTarget = [0 0 10];
disp('Target changed by property')
dispprops(ax)
camtarget([0 0 20])
disp('Target changed by function')
dispprops(ax)

% Change position
ax.CameraPosition = [-30 -40 70];
disp('Position changed by property')
dispprops(ax)
campos([-30 -40 80])
disp('Position changed by function')
dispprops(ax)

% Change view
ax.View = [45 90];
disp('View changed by property')
dispprops(ax)
view([60 60])
disp('View changed by function')
dispprops(ax)

function dispprops(ax)
viewfromax = ax.View %#ok
[azfromfun,elfromfun] = view;
disp(['viewfromfun = ' num2str(azfromfun) ',' num2str(elfromfun)])
posfromax  = ax.CameraPosition %#ok
disp(['posfromfun = ' num2str(campos)])
targetfromax = ax.CameraTarget %#ok
disp(['targetfromfun = ' num2str(camtarget)])
end

There are two things that seem odd to me:

1) Changes via the ax properties are stored, but don't do anything in the plot (even if the respective modes are set to manual). On the other hand, changes via functions are not stored in the properties, but do modify the plot. So what are the properties actually good for?

2) Changes to position and target do not change the view values, but view on the other hand does change target and position. Shouldn't the dependency be mutual? I. e. aren't azimuth and elevation determined by camera position and target (since target and position are independent from each other, c. f. https://mathworks.com/help/matlab/creating_plots/defining-scenes-with-camera-graphics.html)?

Answer 1

[Voss]

When you do

ax = get(gca);

you are storing the axes properties in a struct called ax. (In this case these are the initial properties of the axes, since you do this before anything else.) Setting values of fields in ax doesn't affect the axes itself:

ax.View

ans = 1×2

0 90

ax.View = [0 0]

ax = struct with fields:
              CameraPosition: [0.5000 0.5000 9.1603]
          CameraPositionMode: 'auto'
                CameraTarget: [0.5000 0.5000 0.5000]
            CameraTargetMode: 'auto'
              CameraUpVector: [0 1 0]
          CameraUpVectorMode: 'auto'
             CameraViewAngle: 6.6086
         CameraViewAngleMode: 'auto'
                        View: [0 0]
                  Projection: 'orthographic'
     LabelFontSizeMultiplier: 1.1000
           AmbientLightColor: [1 1 1]
             DataAspectRatio: [1 1 1]
         DataAspectRatioMode: 'auto'
          PlotBoxAspectRatio: [1 0.7897 0.7897]
      PlotBoxAspectRatioMode: 'auto'
                    FontName: 'Helvetica'
                   FontAngle: 'normal'
                  FontWeight: 'normal'
               FontSmoothing: on
        TickLabelInterpreter: 'tex'
                        XLim: [0 1]
                    XLimMode: 'auto'
                        YLim: [0 1]
                    YLimMode: 'auto'
                        ZLim: [0 1]
                    ZLimMode: 'auto'
                XLimitMethod: 'tickaligned'
                YLimitMethod: 'tickaligned'
                ZLimitMethod: 'tickaligned'
                        XDir: 'normal'
                        YDir: 'normal'
                        ZDir: 'normal'
                        CLim: [0 1]
                    CLimMode: 'auto'
                        ALim: [0 1]
                    ALimMode: 'auto'
                    Colormap: [256×3 double]
                    Alphamap: [0 0.0159 0.0317 0.0476 0.0635 0.0794 0.0952 0.1111 0.1270 0.1429 0.1587 0.1746 0.1905 0.2063 0.2222 0.2381 0.2540 0.2698 0.2857 0.3016 0.3175 0.3333 0.3492 0.3651 0.3810 0.3968 0.4127 0.4286 0.4444 0.4603 0.4762 0.4921 … ]
                       Layer: 'bottom'
                  TickLength: [0.0100 0.0250]
               GridLineStyle: '-'
          MinorGridLineStyle: ':'
               XAxisLocation: 'bottom'
                      XColor: [0.1500 0.1500 0.1500]
                  XColorMode: 'auto'
                       XTick: [0 0.2000 0.4000 0.6000 0.8000 1]
                   XTickMode: 'auto'
          XTickLabelRotation: 0
      XTickLabelRotationMode: 'auto'
                      XLabel: [1×1 Text]
                      XScale: 'linear'
                  XTickLabel: {6×1 cell}
              XTickLabelMode: 'auto'
                  XMinorTick: off
               YAxisLocation: 'left'
                      YColor: [0.1500 0.1500 0.1500]
                  YColorMode: 'auto'
                       YTick: [0 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000 1]
                   YTickMode: 'auto'
          YTickLabelRotation: 0
      YTickLabelRotationMode: 'auto'
                      YLabel: [1×1 Text]
                      YScale: 'linear'
                  YTickLabel: {11×1 cell}
              YTickLabelMode: 'auto'
                  YMinorTick: off
                      ZColor: [0.1500 0.1500 0.1500]
                  ZColorMode: 'auto'
                       ZTick: [0 0.5000 1]
                   ZTickMode: 'auto'
          ZTickLabelRotation: 0
      ZTickLabelRotationMode: 'auto'
                      ZLabel: [1×1 Text]
                      ZScale: 'linear'
                  ZTickLabel: ''
              ZTickLabelMode: 'auto'
                  ZMinorTick: off
                    BoxStyle: 'back'
                   LineWidth: 0.5000
                       Color: [1 1 1]
               ClippingStyle: '3dbox'
                CurrentPoint: [2×3 double]
                  ColorScale: 'linear'
                  AlphaScale: 'linear'
                       Title: [1×1 Text]
    TitleHorizontalAlignment: 'center'
                    Subtitle: [1×1 Text]
                       XAxis: [1×1 NumericRuler]
                       ZAxis: [1×1 NumericRuler]
                       XGrid: off
                  XMinorGrid: off
                       YGrid: off
                  YMinorGrid: off
                       ZGrid: off
                  ZMinorGrid: off
                       YAxis: [1×1 NumericRuler]
                       Units: 'normalized'
                    Position: [0.1300 0.1100 0.7750 0.8150]
               InnerPosition: [0.1300 0.1100 0.7750 0.8150]
               OuterPosition: [0 0 1 1]
          PositionConstraint: 'outerposition'
                  TightInset: [0.0459 0.0543 0.0182 0.0208]
                  ColorOrder: [7×3 double]
             ColorOrderIndex: 1
              LineStyleOrder: '-'
         LineStyleOrderIndex: 1
             NextSeriesIndex: 1
                   FontUnits: 'points'
                    FontSize: 10
                FontSizeMode: 'auto'
             TitleFontWeight: 'bold'
          SubtitleFontWeight: 'normal'
     TitleFontSizeMultiplier: 1.1000
                  SortMethod: 'childorder'
                     TickDir: 'in'
                 TickDirMode: 'auto'
                   GridColor: [0.1500 0.1500 0.1500]
               GridColorMode: 'auto'
              MinorGridColor: [0.1000 0.1000 0.1000]
          MinorGridColorMode: 'auto'
                   GridAlpha: 0.1500
               GridAlphaMode: 'auto'
              MinorGridAlpha: 0.2500
          MinorGridAlphaMode: 'auto'
                    Clipping: on
                    NextPlot: 'replace'
                     Toolbar: [1×1 AxesToolbar]
                Interactions: [1×1 matlab.graphics.interaction.interface.DefaultAxesInteractionSet]
                         Box: off
                    Children: [0×0 GraphicsPlaceholder]
                      Parent: [1×1 Figure]
                     Visible: on
            HandleVisibility: 'on'
                      Layout: [0×0 matlab.ui.layout.LayoutOptions]
               ButtonDownFcn: ''
                 ContextMenu: [0×0 GraphicsPlaceholder]
                  BusyAction: 'queue'
                BeingDeleted: off
               Interruptible: on
                   CreateFcn: ''
                   DeleteFcn: ''
                        Type: 'axes'
                         Tag: ''
                    UserData: []
                    Selected: off
          SelectionHighlight: on
                     HitTest: on
               PickableParts: 'visible'
                      Legend: [0×0 GraphicsPlaceholder]

% actual View is still [0 90] because 'View' was set 
% in ax, which is a copy of the axes properties
get(gca,'View')

ans = 1×2

0 90

Store the axes itself instead:

ax = gca;

and the properties will be accurate after they are set, regardless of how they are set.

peaks(30);

 
z =  3*(1-x).^2.*exp(-(x.^2) - (y+1).^2) ... 
   - 10*(x/5 - x.^3 - y.^5).*exp(-x.^2-y.^2) ... 
   - 1/3*exp(-(x+1).^2 - y.^2) 
 

% ax=get(gca);
ax = gca;
% Display values
disp('Initial values')

Initial values

dispprops(ax)

viewfromax = 1×2

-37.5000 30.0000

viewfromfun = -37.5,30

posfromax = 1×3

-27.3943 -35.7009 63.3693

posfromfun = -27.3943     -35.7009      63.3693

targetfromax = 1×3

0 0 0.7954

targetfromfun = 0           0      0.7954

% Change target
ax.CameraTarget = [0 0 10];
disp('Target changed by property')

Target changed by property

dispprops(ax)

viewfromax = 1×2

-37.5000 30.0000

viewfromfun = -37.5,30

posfromax = 1×3

-27.3943 -35.7009 63.3693

posfromfun = -27.3943     -35.7009      63.3693

targetfromax = 1×3

0 0 10

targetfromfun = 0   0  10

camtarget([0 0 20])
disp('Target changed by function')

Target changed by function

dispprops(ax)

viewfromax = 1×2

-37.5000 30.0000

viewfromfun = -37.5,30

posfromax = 1×3

-27.3943 -35.7009 63.3693

posfromfun = -27.3943     -35.7009      63.3693

targetfromax = 1×3

0 0 20

targetfromfun = 0   0  20

% Change position
ax.CameraPosition = [-30 -40 70];
disp('Position changed by property')

Position changed by property

dispprops(ax)

viewfromax = 1×2

-37.5000 30.0000

viewfromfun = -37.5,30

posfromax = 1×3

-30 -40 70

posfromfun = -30 -40  70

targetfromax = 1×3

0 0 20

targetfromfun = 0   0  20

campos([-30 -40 80])
disp('Position changed by function')

Position changed by function

dispprops(ax)

viewfromax = 1×2

-37.5000 30.0000

viewfromfun = -37.5,30

posfromax = 1×3

-30 -40 80

posfromfun = -30 -40  80

targetfromax = 1×3

0 0 20

targetfromfun = 0   0  20

% Change view
ax.View = [45 90];
disp('View changed by property')

View changed by property

dispprops(ax)

viewfromax = 1×2

45 90

viewfromfun = 45,90

posfromax = 1×3

0 0 125.9431

posfromfun = 0             0      125.9431

targetfromax = 1×3

0 0 0.7954

targetfromfun = 0           0      0.7954

view([60 60])

disp('View changed by function')

View changed by function

dispprops(ax)

viewfromax = 1×2

60 60

viewfromfun = 60,60

posfromax = 1×3

22.5000 -12.9904 109.1765

posfromfun = 22.5     -12.99038      109.1765

targetfromax = 1×3

0 0 0.7954

targetfromfun = 0           0      0.7954

function dispprops(ax)
viewfromax = ax.View %#ok
[azfromfun,elfromfun] = view;
disp(['viewfromfun = ' num2str(azfromfun) ',' num2str(elfromfun)])
posfromax  = ax.CameraPosition %#ok
disp(['posfromfun = ' num2str(campos)])
targetfromax = ax.CameraTarget %#ok
disp(['targetfromfun = ' num2str(camtarget)])
end

[Voss]

@broken_arrow's comment (posted as an Answer) moved here:

"Ok, so get() makes all the difference (yikes). I get() that now ;). How about the second part? How come view is independent from position and target?"

[Voss]

It looks like it's because the properties don't update instantly, but only when the next drawnow (or other command that processes the graphics event queue such as figure or pause) occurs.

Here's an example where CameraPosition is set and then View is queried afterward. In Case 1 no drawnow is used and View remains at its old value, and in Case 2 drawnow is used in between setting CameraPosition and getting View, and View shows the updated value:

% First, a reference figure with default axes 'View' and 
% 'CameraPosition' properties shown:
figure();
peaks(30);

 
z =  3*(1-x).^2.*exp(-(x.^2) - (y+1).^2) ... 
   - 10*(x/5 - x.^3 - y.^5).*exp(-x.^2-y.^2) ... 
   - 1/3*exp(-(x+1).^2 - y.^2) 
 

ax = gca();
get(ax,'View')

ans = 1×2

-37.5000 30.0000

get(ax,'CameraPosition')

ans = 1×3

-27.3943 -35.7009 63.3693

% Case 1: 
% when setting 'CameraPosition', 'View' property doesn't change
% (but actual apparent 'View' does):
figure();
peaks(30);

 
z =  3*(1-x).^2.*exp(-(x.^2) - (y+1).^2) ... 
   - 10*(x/5 - x.^3 - y.^5).*exp(-x.^2-y.^2) ... 
   - 1/3*exp(-(x+1).^2 - y.^2) 
 

ax = gca();
get(ax,'View')

ans = 1×2

-37.5000 30.0000

get(ax,'CameraPosition')

ans = 1×3

-27.3943 -35.7009 63.3693

set(ax,'CameraPosition',[0 -40 80])

% still the old View (but clearly the surface is seen 
% from a different angle than in the first figure)
get(ax,'View') 

ans = 1×2

-37.5000 30.0000

% Case 2: 
% putting a drawnow() after setting 'CameraPosition'
% causes 'View' property to show the updated value:
figure();
peaks(30);

 
z =  3*(1-x).^2.*exp(-(x.^2) - (y+1).^2) ... 
   - 10*(x/5 - x.^3 - y.^5).*exp(-x.^2-y.^2) ... 
   - 1/3*exp(-(x+1).^2 - y.^2) 
 

ax = gca();
get(ax,'View')

ans = 1×2

-37.5000 30.0000

get(ax,'CameraPosition')

ans = 1×3

-27.3943 -35.7009 63.3693

set(ax,'CameraPosition',[0 -40 80])

drawnow()
get(ax,'View') % now View is accurate

ans = 1×2

0 39.4248

[broken_arrow]

Thank you very much. It seems to be a little tricky: Apparently view does actually change when modifying CameraPosition, but a query in a script/function immediately after a change may return the outdated value because execution proceeds "too fast". The same query in the command window will return the correct value. drawnow has the same effect because it enforces waiting for the "figure update queue" to finish.

But I still do not fully comprehend the relationship between View, CameraTarget and CameraPosition. I always imagined the line between target and position as the optical axis of the camera, which can be alternatively defined by azimuth and elevation. But that seems to be incorrect. For example, a change of CameraTarget does not change View and CameraPosition, but rather modifies CameraViewAngle. Can someone explain?

Update: Accepted answer, comment moved to follow up question: https://de.mathworks.com/matlabcentral/answers/1690635-relationship-between-view-cameratarget-cameraposition-cameraviewangle-properties