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Fix ambiguities in spec inertial documentation #990

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May 6, 2022
Merged

Fix ambiguities in spec inertial documentation #990

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e754f60
inertial.sdf spec: improve documentation
scpeters Apr 17, 2022
9e9ce18
Add missing xml closing tag
scpeters Apr 19, 2022
0a57cd6
Add link to Mathworks documentation
scpeters Apr 19, 2022
77630dd
Replace ’ with more standard ' character
scpeters Apr 19, 2022
a812c25
Merge branch 'sdf12' into formalize_inertial_spec_doc
scpeters Apr 19, 2022
1c5df36
Fix MathWorks capitalization
scpeters Apr 19, 2022
43f2f84
Copy changes to spec versions 1.4, 1.8
scpeters May 3, 2022
fc0ba0a
Copy changes to spec version 1.5, 1.6, 1.7
scpeters May 3, 2022
4f9487f
Merge branch 'sdf12' into formalize_inertial_spec_doc
scpeters May 3, 2022
2a62ad1
Revert quaternions in older spec
scpeters May 4, 2022
0538d73
Merge branch 'sdf12' into formalize_inertial_spec_doc
scpeters May 5, 2022
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60 changes: 51 additions & 9 deletions sdf/1.4/inertial.sdf
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,34 +1,76 @@
<!-- Inertial -->
<element name="inertial" required="0">
<description>The inertial properties of the link.</description>
<description>
The link's mass, position of its center of mass, and its central inertia
properties.
</description>

<element name="mass" type="double" default="1.0" required="0">
<description>The mass of the link.</description>
</element>

<element name="pose" type="pose" default="0 0 0 0 0 0" required="0">
<description>This is the pose of the inertial reference frame, relative to the link reference frame. The origin of the inertial reference frame needs to be at the center of gravity. The axes of the inertial reference frame do not need to be aligned with the principal axes of the inertia.</description>
<description>
This pose (translation, rotation) describes the position and orientation
of the link's center-of-mass-frame C relative to the link-frame L.
The first three components (x y z) specify the position vector from Lo
(the link-frame origin) to Co (the link's center of mass) as
`x L̂x + y L̂y + z L̂ᴢ`, where L̂x, L̂y, L̂ᴢ are link-frame L's orthogonal unit
vectors. The subsequent values characterize C's orientation relative to
link-frame L as a sequence of Euler rotations
(r p y) documented in http://sdformat.org/tutorials?tut=specify_pose.
</description>
</element>

<element name="inertia" required="0">
<description>The 3x3 rotational inertia matrix. Because the rotational inertia matrix is symmetric, only 6 above-diagonal elements of this matrix are specified here, using the attributes ixx, ixy, ixz, iyy, iyz, izz.</description>
<description>
This link's moments of inertia ixx, iyy, izz and products of inertia
ixy, ixz, iyz about Co (the link's center of mass) for the unit vectors
Ĉx, Ĉy, Ĉᴢ fixed in the center-of-mass-frame C.
Note: the orientation of Ĉx, Ĉy, Ĉᴢ relative to L̂x, L̂y, L̂ᴢ is specified
by the `pose` tag.
To avoid compatibility issues associated with the negative sign
convention for product of inertia, align Ĉx, Ĉy, Ĉᴢ with principal
inertia directions so that all the products of inertia are zero.
For more information about this sign convention, see the following
MathWorks documentation for working with CAD tools:
https://www.mathworks.com/help/releases/R2021b/physmod/sm/ug/specify-custom-inertia.html#mw_b043ec69-835b-4ca9-8769-af2e6f1b190c
</description>
<element name="ixx" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉx.
</description>
</element>
<element name="ixy" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉy, where the product of inertia convention -m x y (not +m x y)
is used. If Ĉx or Ĉy is a principal inertia direction, ixy = 0.
</description>
</element>
<element name="ixz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉz, where the product of inertia convention -m x z (not +m x z)
is used. If Ĉx or Ĉz is a principal inertia direction, ixz = 0.
</description>
</element>
<element name="iyy" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉy.
</description>
</element>
<element name="iyz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉy and Ĉz, where the product of inertia convention -m y z (not +m y z)
is used. If Ĉy or Ĉz is a principal inertia direction, iyz = 0.
</description>
</element>
<element name="izz" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉz.
</description>
</element>
</element> <!-- End Inertia -->
</element> <!-- End Inertial -->
63 changes: 54 additions & 9 deletions sdf/1.5/inertial.sdf
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
<!-- Inertial -->
<element name="inertial" required="0">
<description>The inertial properties of the link.</description>
<description>
The link's mass, position of its center of mass, and its central inertia
properties.
</description>

<element name="mass" type="double" default="1.0" required="0">
<description>The mass of the link.</description>
Expand All @@ -9,28 +12,70 @@
<include filename="frame.sdf" required="*"/>

<include filename="pose.sdf" required="0">
<description>This is the pose of the inertial reference frame, relative to the specified reference frame. The origin of the inertial reference frame needs to be at the center of gravity. The axes of the inertial reference frame do not need to be aligned with the principal axes of the inertia.</description>
<description>
This pose (translation, rotation) describes the position and orientation
of the link's center-of-mass-frame C relative to the frame specified in the @frame attribute.
If the @frame attribute is empty or unspecified, then the link frame L
is used. In this case,
the first three components (x y z) specify the position vector from Lo
(the link-frame origin) to Co (the link's center of mass) as
`x L̂x + y L̂y + z L̂ᴢ`, where L̂x, L̂y, L̂ᴢ are link-frame L's orthogonal unit
vectors. The subsequent values characterize C's orientation relative to
link-frame L as a sequence of Euler rotations
(r p y) documented in http://sdformat.org/tutorials?tut=specify_pose,
or as a quaternion (x y z w), where w is the scalar component.
</description>
</include>

<element name="inertia" required="0">
<description>The 3x3 rotational inertia matrix. Because the rotational inertia matrix is symmetric, only 6 above-diagonal elements of this matrix are specified here, using the attributes ixx, ixy, ixz, iyy, iyz, izz.</description>
<description>
This link's moments of inertia ixx, iyy, izz and products of inertia
ixy, ixz, iyz about Co (the link's center of mass) for the unit vectors
Ĉx, Ĉy, Ĉᴢ fixed in the center-of-mass-frame C.
Note: the orientation of Ĉx, Ĉy, Ĉᴢ relative to L̂x, L̂y, L̂ᴢ is specified
by the `pose` tag.
To avoid compatibility issues associated with the negative sign
convention for product of inertia, align Ĉx, Ĉy, Ĉᴢ with principal
inertia directions so that all the products of inertia are zero.
For more information about this sign convention, see the following
MathWorks documentation for working with CAD tools:
https://www.mathworks.com/help/releases/R2021b/physmod/sm/ug/specify-custom-inertia.html#mw_b043ec69-835b-4ca9-8769-af2e6f1b190c
</description>
<element name="ixx" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉx.
</description>
</element>
<element name="ixy" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉy, where the product of inertia convention -m x y (not +m x y)
is used. If Ĉx or Ĉy is a principal inertia direction, ixy = 0.
</description>
</element>
<element name="ixz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉz, where the product of inertia convention -m x z (not +m x z)
is used. If Ĉx or Ĉz is a principal inertia direction, ixz = 0.
</description>
</element>
<element name="iyy" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉy.
</description>
</element>
<element name="iyz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉy and Ĉz, where the product of inertia convention -m y z (not +m y z)
is used. If Ĉy or Ĉz is a principal inertia direction, iyz = 0.
</description>
</element>
<element name="izz" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉz.
</description>
</element>
</element> <!-- End Inertia -->
</element> <!-- End Inertial -->
63 changes: 54 additions & 9 deletions sdf/1.6/inertial.sdf
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,6 +1,9 @@
<!-- Inertial -->
<element name="inertial" required="0">
<description>The inertial properties of the link.</description>
<description>
The link's mass, position of its center of mass, and its central inertia
properties.
</description>

<element name="mass" type="double" default="1.0" required="0">
<description>The mass of the link.</description>
Expand All @@ -9,28 +12,70 @@
<include filename="frame.sdf" required="*"/>

<include filename="pose.sdf" required="0">
<description>This is the pose of the inertial reference frame, relative to the specified reference frame. The origin of the inertial reference frame needs to be at the center of gravity. The axes of the inertial reference frame do not need to be aligned with the principal axes of the inertia.</description>
<description>
This pose (translation, rotation) describes the position and orientation
of the link's center-of-mass-frame C relative to the frame specified in the @frame attribute.
If the @frame attribute is empty or unspecified, then the link frame L
is used. In this case,
the first three components (x y z) specify the position vector from Lo
(the link-frame origin) to Co (the link's center of mass) as
`x L̂x + y L̂y + z L̂ᴢ`, where L̂x, L̂y, L̂ᴢ are link-frame L's orthogonal unit
vectors. The subsequent values characterize C's orientation relative to
link-frame L as a sequence of Euler rotations
(r p y) documented in http://sdformat.org/tutorials?tut=specify_pose,
or as a quaternion (x y z w), where w is the scalar component.
</description>
</include>

<element name="inertia" required="0">
<description>The 3x3 rotational inertia matrix. Because the rotational inertia matrix is symmetric, only 6 above-diagonal elements of this matrix are specified here, using the attributes ixx, ixy, ixz, iyy, iyz, izz.</description>
<description>
This link's moments of inertia ixx, iyy, izz and products of inertia
ixy, ixz, iyz about Co (the link's center of mass) for the unit vectors
Ĉx, Ĉy, Ĉᴢ fixed in the center-of-mass-frame C.
Note: the orientation of Ĉx, Ĉy, Ĉᴢ relative to L̂x, L̂y, L̂ᴢ is specified
by the `pose` tag.
To avoid compatibility issues associated with the negative sign
convention for product of inertia, align Ĉx, Ĉy, Ĉᴢ with principal
inertia directions so that all the products of inertia are zero.
For more information about this sign convention, see the following
MathWorks documentation for working with CAD tools:
https://www.mathworks.com/help/releases/R2021b/physmod/sm/ug/specify-custom-inertia.html#mw_b043ec69-835b-4ca9-8769-af2e6f1b190c
</description>
<element name="ixx" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉx.
</description>
</element>
<element name="ixy" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉy, where the product of inertia convention -m x y (not +m x y)
is used. If Ĉx or Ĉy is a principal inertia direction, ixy = 0.
</description>
</element>
<element name="ixz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉz, where the product of inertia convention -m x z (not +m x z)
is used. If Ĉx or Ĉz is a principal inertia direction, ixz = 0.
</description>
</element>
<element name="iyy" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉy.
</description>
</element>
<element name="iyz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉy and Ĉz, where the product of inertia convention -m y z (not +m y z)
is used. If Ĉy or Ĉz is a principal inertia direction, iyz = 0.
</description>
</element>
<element name="izz" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉz.
</description>
</element>
</element> <!-- End Inertia -->
</element> <!-- End Inertial -->
63 changes: 54 additions & 9 deletions sdf/1.7/inertial.sdf
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,34 +1,79 @@
<!-- Inertial -->
<element name="inertial" required="0">
<description>The inertial properties of the link.</description>
<description>
The link's mass, position of its center of mass, and its central inertia
properties.
</description>

<element name="mass" type="double" default="1.0" required="0">
<description>The mass of the link.</description>
</element>

<include filename="pose.sdf" required="0">
<description>This is the pose of the inertial reference frame, relative to the specified reference frame. The origin of the inertial reference frame needs to be at the center of gravity. The axes of the inertial reference frame do not need to be aligned with the principal axes of the inertia.</description>
<description>
This pose (translation, rotation) describes the position and orientation
of the link's center-of-mass-frame C relative to the frame specified in the @relative_to attribute.
If the @relative_to attribute is empty or unspecified, then the link frame L
is used. In this case,
the first three components (x y z) specify the position vector from Lo
(the link-frame origin) to Co (the link's center of mass) as
`x L̂x + y L̂y + z L̂ᴢ`, where L̂x, L̂y, L̂ᴢ are link-frame L's orthogonal unit
vectors. The subsequent values characterize C's orientation relative to
link-frame L as a sequence of Euler rotations
(r p y) documented in http://sdformat.org/tutorials?tut=specify_pose,
or as a quaternion (x y z w), where w is the scalar component.
</description>
</include>

<element name="inertia" required="0">
<description>The 3x3 rotational inertia matrix. Because the rotational inertia matrix is symmetric, only 6 above-diagonal elements of this matrix are specified here, using the attributes ixx, ixy, ixz, iyy, iyz, izz.</description>
<description>
This link's moments of inertia ixx, iyy, izz and products of inertia
ixy, ixz, iyz about Co (the link's center of mass) for the unit vectors
Ĉx, Ĉy, Ĉᴢ fixed in the center-of-mass-frame C.
Note: the orientation of Ĉx, Ĉy, Ĉᴢ relative to L̂x, L̂y, L̂ᴢ is specified
by the `pose` tag.
To avoid compatibility issues associated with the negative sign
convention for product of inertia, align Ĉx, Ĉy, Ĉᴢ with principal
inertia directions so that all the products of inertia are zero.
For more information about this sign convention, see the following
MathWorks documentation for working with CAD tools:
https://www.mathworks.com/help/releases/R2021b/physmod/sm/ug/specify-custom-inertia.html#mw_b043ec69-835b-4ca9-8769-af2e6f1b190c
</description>
<element name="ixx" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉx.
</description>
</element>
<element name="ixy" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉy, where the product of inertia convention -m x y (not +m x y)
is used. If Ĉx or Ĉy is a principal inertia direction, ixy = 0.
</description>
</element>
<element name="ixz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉx and Ĉz, where the product of inertia convention -m x z (not +m x z)
is used. If Ĉx or Ĉz is a principal inertia direction, ixz = 0.
</description>
</element>
<element name="iyy" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉy.
</description>
</element>
<element name="iyz" type="double" default="0.0" required="1">
<description></description>
<description>
The link's product of inertia about Co (the link's center of mass) for
Ĉy and Ĉz, where the product of inertia convention -m y z (not +m y z)
is used. If Ĉy or Ĉz is a principal inertia direction, iyz = 0.
</description>
</element>
<element name="izz" type="double" default="1.0" required="1">
<description></description>
<description>
The link's moment of inertia about Co (the link's center of mass) for Ĉz.
</description>
</element>
</element> <!-- End Inertia -->
</element> <!-- End Inertial -->
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