# [Gimp-gui] Inconsistencies in angle of rotation measurements

*From*: Elle Stone <ellestone ninedegreesbelow com>
*To*: gimp-gui-list <gimp-gui-list gnome org>
*Subject*: [Gimp-gui] Inconsistencies in angle of rotation measurements
*Date*: Tue, 13 Mar 2018 08:44:57 -0400

`Stopping to add/subtract the appropriate angle to make various tools and
``filters match the angle measured by the Measure Tool is a bit of an
``interruption.
`

`Is there an option somewhere (that I haven't found - I looked in the
``toolbox and in Preferences) to tell the Measure Tool to show angles from
``0 to 360 counterclockwise to match the angles shown by the Paint Tools?
`

`And a second option to tell the Measure Tool to show angles from 0 to
``+/- 180 degrees to match the layer arbitrary rotation operation?
`

`And a third option to tell the Measure Tool to show angles from 0 to 360
``degrees *clockwise*, to match Filters that measure angles clockwise
``instead of counterclockwise from the positive x-axis? And etc if there
``are other starting points/directions for other Filters/operations that
``take angles as user input?
`

`If there aren't already such options available, maybe it would be a good
``idea to have all angle measurements for all tools and filters be
``counterclockwise from zero at the positive x-axis? Though some angle
``measurements are more comfortably done starting from 0 degrees at the
``positive y axis.
`
Here are various ways current GIMP tools and operations measure angles:

`* The "click/shift to position and paint" angle measurements measure
``counterclockwise from zero to 360 degrees, with zero being at the
``positive x-axis.
`

`* Filters/Blur/Circular Motion Blur and Linear Motion Blur angle of blur
``both run from 0 to 360, counterclockwise (matches the Paint tools).
`

`* The "View/Rotate View/Other Rotation Angle" angle of rotation
``measurements from 0 to 360, but *clockwise* (opposite direction from the
``Paint tools) from the positive x-axis.
`

`* For arbitrary rotation of a layer, the rotation measurements from
``always from 0 at the positive y-axis, running from -180
``(counterclockwise) degrees to +180 (clockwise) degrees.
`

`* The "Measure Tool" measures the angle from the closest of the positive
``and negative x axes. So the maximum angle the Measure Tool will show is
``90 degrees, which means there are four angles (one per quadrant) that
``measure 1 degree, four angles that measure 2 degrees, four that measure
``3 degrees, and so on, all the way from "just over 0" to "just under 90
``degrees", with 0 and 90 degrees only being measured at two angles each,
``being the positive and negative x and y axes, respectively.
`

`Rotating a layer or selection to match an angle measured by the Measure
``Tool requires some fairly complicated adding/subtracting. Let's say you
``measured an angle of 27 degrees in the third quadrant. So starting from
``0 rotation, add 90 degrees to get to the negative x-axis, and then add
``27 more degrees, so rotate the layer or selection by 90+27=117 degrees.
`

`Painting a straight line at a given angle that was measured using the
``Measure Tool requires adding/subtracting 0 or 90 or 180 or 270 degrees,
``depending on the direction of the painted line vs the angle measured by
``the Measure Tool.
`
And etc.
Here are some possibly relevant bug reports:

`add easy way to set rotation angle to straighten an image:
``https://bugzilla.gnome.org/show_bug.cgi?id=526719
`

`Measure tool: saveable preset parameters:
``https://bugzilla.gnome.org/show_bug.cgi?id=679562
`

`The Angle range in brush dynamics should be -180°/+180° and not 0°-360°:
``https://bugzilla.gnome.org/show_bug.cgi?id=787651
`

`implement free angled guides:
``https://bugzilla.gnome.org/show_bug.cgi?id=344109
`
Best,
Elle

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