Comparison of Plot Coordinate Systems
The figures below compare identical Row Profile plots using the systems of Pixel Coordinates and World Coordinates for the same image data.
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You can change the x and y axis labels, the caption, axis extent, and other attributes afterwards using the Plot Attributes dialog. |
Below are shown two comparisons. The first pair of plots shows pixel and world coordinate plots for an image that does not have a World Coordinate System calibration. The second pair shows the same plots for an image having a World Coordinate Calibration. In both cases, Pixel plots use the coordinate value on the x-axis, whereas World coordinate plots show relative position on the x-axis. Relative position is computed relative to the center of the central pixel being plotted.
If the image has no world coordinate calibration, you can still get a plot when the Plot Coordinate is set to World. In this case, the world coordinate plot uses position difference on the x-axis with the center at coordinate "0", whereas the Pixel coordinate mode uses column (or row) number on the x-axis.
The first figure below shows the Row Profile plot in the Pixel Coordinate System. The x-axis measures the column number on the image. The plot caption "Row [138:183, 459]" indicates that the plot data are from columns 138 through 183 (46 total columns) in row 459.
The next figure below shows the same image data plotted in the World Coordinate System. The plot caption lists the column,row span like above but also lists the world coordinate distance relative to the central pixel. This image has no world coordinate calibration, so the position is the (column,row) position of the central pixel.
The first figure below shows the Row Profile plot in the Pixel coordinate system. The plot caption "Row [998:1043, 643]" indicates that the plot data are from columns 998 through 1043 (46 total columns) in row 643.
The next figure below shows the same image data plotted in the World Coordinate System. The plot caption lists the column,row span like above but also lists the world coordinates (right ascension, declination) at the middle of the central pixel. The row data are plotted relative to this point in units of arcseconds. Notice that the plot caption lists the world coordinates of the center of the central pixel.
Plot Windows, Plot Coordinate Systems, World Coordinate System