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Filling out the Geometry Orbiter Class

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The Geometry_Orbiter class provides geometric values related to an orbiting or flyby spacecraft observation. The values in this class are specific to a single reference frame at a single reference time (or time range) for at most a single target. You may repeat this class with differing values for one or all of those, if appropriate to the observation being labelled.

Contents

<geometry_reference_time>

OPTIONAL

This is the UTC time for which the values in this class have been calculated. It must be in the standard YYYY-MM-DDThh:mm:ss.sssZ" format.

Either this attribute, or the geometry_start_time/geometry_stop_timepair is required. You are not prevented from including both, but that would be rather confusing and there is no place in this class for an explanatory comment - so avoid it.

<geometry_start_time> and <geometry_stop_time>

OPTIONAL

These are both optional, but if you use one you must also include the other. (See also the note above for geometry_reference_time.) Use the start/stop pair when you have an extended observation for which you plan to provide pairs of geometric values corresponding to these times in the other subclasses of <Geometry_Orbiter>.

These must be UTC times in the standard YYYY-MM-DDThh:mm:ss.sssZ" format.

<Orbiter_Identification>

OPTIONAL

Use this class to identify geometric elements and reference points to be used in the Geometry_Orbiter subclasses that follow.

<Central_Body_Identification>

OPTIONAL

If the target of the following geometry is orbiting another body, that body is the "central body" and should be identified using this class. It is filled out identically to the class of the same name on the Filling Out the Image_Display_Geometry Class page on this wiki.

<Geometry_Target_Identification>

OPTIONAL

This class locally defines the concept of "target" to be the thing on the "to" end of the various vectors that follow in this Geometry_Orbiter class. It may or may not be the same as the target of the product as a whole. It is filled out identically to the class of the same name in the Image_Display_Geometry class.

<Coordinate_System_Identification>

OPTIONAL

This class is used to identify a "coordinate system" in the NAIF SPICE toolkit sense - both a reference frame and a well-defined origin, with a specific type of coordinates.

<coordinate_system_type>

REQUIRED

You must indicate the type of coordinates to be applied, which must be one of the following values:

  • Azimuth-Elevation
  • Cartesian
  • Planetocentric
  • Planetodetic
  • Planetographic
  • Spherical

<coordinate_system_time>

OPTIONAL

If your coordinate system has a time dependence, this attribute should hold the relevant instantiation time in UTC, in the standard YYYY-MM-DDThh:mm:ss.ssZ format.

<comment>

OPTIONAL

Here is a place to add some clarifying explanation for uncommon coordinate systems.

<Coordinate_System_Origin_Identification>

REQUIRED

This class indicates the fixed origin ([0,0,0] point, i.e.) of the coordinate system. Apart from the class name, the content is filled out identically to the Geometry_Target_Identification class in the Image_Display_Geometry class. That is, its attributes are:

  • body_spice_name
  • name
  • Internal_Reference

<Reference_Frame_Identification>

REQUIRED

This class indicates the "orthogonal axes" part of the coordinate system definition. It is filled out identically to the class of the same name in the Image_Display_Geometry class.


<Pixel_Dimensions>

OPTIONAL

This class provides various ways of translating a pixel field of view to physical dimensions. You must provide units for these attributes as appropriate.

<pixel_field_of_view_method>

REQUIRED

This attribute indicates how the pixel FOV values, following, were derived. It must have one of the following values:

  • average: The pixel FOV varies across the image; the value stated are the average FOV.
  • central pixel: The pixel FOV varies across the image; the value stated represents the FOV of the center pixel.
  • constant: The pixel FOV does not vary across the image.

<horizontal_pixel_field_of_view>

OPTIONAL

This attribute gives the horizontal (as defined by the <Display_Direction> class) FOV of a single pixel in terms of its angular size. You must specify angular units (typically "deg") for this value.

<vertical_pixel_field_of_view>

OPTIONAL

This attribute gives the vertical (as defined by the <Display_Direction> class) FOV of a single pixel in terms of its angular size. You must specify angular units (typically "deg") for this value.

<Pixel_Size_Projected>

OPTIONAL

This class provides a the size, in units of length, of a single pixel projected onto the surface of (or at the distance of) the relevant geometry target.

<reference_location>

OPTIONAL

This attribute identifies the point on the target at which the following pixel values are calculated. Either this or <distance> must be specified. It must have one of the following values:

  • Boresight Intercept Point
  • Constant
  • Subspacecraft Point
  • Target Center

<distance>

OPTIONAL

Distance to which the pixel is projected. This is particularly useful when your target object occupies a small number of pixels rather than the entire image frame. Either this or <reference_location> must be specified. You must provide units of length for this value.

<horizontal_pixel_footprint>

REQUIRED

This attribute gives the horizontal (as defined in the associated Display_Direction class) extent of a single pixel at the reference_location or distance, in units of length.

<vertical_pixel_footprint>

REQUIRED

This attribute gives the vertical (as defined in the associated Display_Direction class) extent of a single pixel at the reference_location or distance, in units of length.


<Distances>

OPTIONAL

This class is a container for other classes used to list scalar distance measurements of various types. These classes collect point-to-point distance measurements (that is, magnitudes rather than vectors) for various named intervals of interest, as well as providing a class for specifying arbitrary distance measurements as needed. Unless otherwise stated, distances are measured center-to-center, and references to "target" and "central body" refer to the objects identified previously in this <Geometry_Orbiter> class.

To avoid a lot of tedious repetition, these class and attribute descriptions are somewhat abbreviated. In general, the containing class will be described briefly, and the individual distance attributes will merely be listed - their names being self-explanatory.

General Notes:

  • All distance attributes are optional in their respective classes; none may be repeated.
  • All distances are considered positive.
  • All distances are named by their start and end points; terms like "target" and "central body" are as defined for this Geometry_Orbiter class.
  • Unless otherwise indicated by their names, all measurements are considered to be center-to-center.
  • All values require units of length for each value, though that unit can vary among attributes in a class. For example:
     <spacecraft_target_center_distance unit="km">15.097</spacecraft_target_center_distance>
     <target_geocentric_distance unit="AU">17.9</target_geocentric_distance>

<comment>

OPTIONAL

Here is a place to provide any additional explanatory text that might be apropos.

<Distances_Specific>

OPTIONAL

This container class lists specific named distances often used for searching through data collections from a single source. Unlike other distance classes, these attributes may be listed in any order.

Distances Included:

  • spacecraft_geocentric_distance
  • spacecraft_heliocentric_distance
  • spacecraft_central_body_distance
  • spacecraft_target_center_distance
  • spacecraft_target_boresight_intercept_distance
  • spacecraft_target_subspacecraft_distance
  • target_geocentric_distance
  • target_heliocentric_distance
  • target_ssb_distance - "SSB" stands for "Solar System Barycenter"

<Distances_Min_Max>

OPTIONAL

This container class lists minimum and maximum distances often used for constraining searches through data collections from a single source. You are required to provide these values in min/max pairs. If you don't have min/max pairs for one or more values, use the <Distances_Specific> class and the corresponding single attribute.

Distances Included:

  • minimum_spacecraft_geocentric_distance
  • maximum_spacecraft_geocentric_distance
  • minimum_spacecraft_heliocentric_distance
  • maximum_spacecraft_heliocentric_distance
  • minimum_spacecraft_central_body_distance
  • maximum_spacecraft_central_body_distance
  • minimum_spacecraft_target_center_distance
  • maximum_spacecraft_target_center_distance
  • minimum_spacecraft_target_boresight_intercept_distance
  • maximum_spacecraft_target_boresight_intercept_distance
  • minimum_spacecraft_target_subspacecraft_distance
  • maximum_spacecraft_target_subspacecraft_distance
  • minimum_target_geocentric_distance
  • maximum_target_geocentric_distance
  • minimum_target_heliocentric_distance
  • maximum_target_heliocentric_distance
  • minimum_target_ssb_distance - "SSB" stands for "Solar System Barycenter"
  • maximum_target_ssb_distance - "SSB" stands for "Solar System Barycenter"

<Distances_Start_Stop>

OPTIONAL

This container class lists distances often used for constraining searches through data collections from a single source calculated at the <geometry_start_time> and <geometry_stop_time> defined at the top of this Geometry_Orbiter class. You are required to provide these values in start/stop pairs. If you don't have start/stop pairs for one or more values, use the <Distances_Specific> class and the corresponding single attribute.

Distances Included:

  • start_spacecraft_geocentric_distance
  • stop_spacecraft_geocentric_distance
  • start_spacecraft_heliocentric_distance
  • stop_spacecraft_heliocentric_distance
  • start_spacecraft_central_body_distance
  • stop_spacecraft_central_body_distance
  • start_spacecraft_target_center_distance
  • stop_spacecraft_target_center_distance
  • start_spacecraft_target_boresight_intercept_distance
  • stop_spacecraft_target_boresight_intercept_distance
  • start_spacecraft_target_subspacecraft_distance
  • stop_spacecraft_target_subspacecraft_distance
  • start_target_geocentric_distance
  • stop_target_geocentric_distance
  • start_target_heliocentric_distance
  • stop_target_heliocentric_distance
  • start_target_ssb_distance - "SSB" stands for "Solar System Barycenter"
  • stop_target_ssb_distance - "SSB" stands for "Solar System Barycenter"

<Distances_Generic>

OPTIONAL

This class is used to define a distance measurement between a starting point, called the "observer", and an ending point, called the "target". You must explicitly identify the "observer" and "target", as well as providing the distance.

<Observer_Identification>

REQUIRED

The class has the same content, and is filled out the same way, as the <Geometry_Target_Identification> class in the Image_Display_Geometry class.

<Geometry_Target_Identification>

REQUIRED

This class is filled out identically to the class of the same name in the Image_Display_Geometry class.

<distance>

REQUIRED

The center-to-center, positive distance between the observer and the target. You must provide units of length for this value.


<Surface_Geometry>

OPTIONAL

This class is a container for other classes used to list surface coordinates of various types. These classes collect surface orientation for various named angles of interest either as single values, min/max ranges, or start/stop values. Concepts like "latitude" and "longitude" are interpreted with respect to the specific target in question, as identified previously in this <Geometry_Orbiter> class.

To avoid some tedious repetition, these class and attribute descriptions are somewhat abbreviated. In general, the containing class will be described briefly, attributes unique to each class will be described as usual, the individual angle attributes will merely be listed with abbreviated descriptions mainly concerning valid ranges.

General Notes:

  • All attributes are optional in their respective classes unless otherwise indicated; none may be repeated.
  • All angles require units of angle for each value. Though that unit can vary among attributes in a class, typically all values will be given in units of degrees. For example:
     <subsolar_azimuth unit="deg">15.097</subsolar_azimuth>
     <spacecraft_longitude unit="deg">17.9</spacecraft_longitude>

<comment>

OPTIONAL

Here is a place to provide any additional explanatory text that might be apropos.

<Surface_Geometry_Specific>

OPTIONAL

This container class lists specific named distances as well as surface intercept points.

<Pixel_Intercept>

OPTIONAL

This class defines the latitude and longitude on the surface of the target for the projection of a single, specified pixel. It may be repeated. Use it when the points involved do not represent the observation footprint.

<reference_pixel_location>

OPTIONAL

This is a human-readable indication of where the reference pixel is, when the image is displayed as indicated in the Image_Display_Geometry class. It must have one of the following values:

  • Center
  • Lower Left Corner
  • Lower Right Corner
  • Upper Left Corner
  • Upper Right Corner
<Reference_Pixel>

OPTIONAL

This is a more precise indication of where the reference pixel occurs in the image. It is filled out identically to the class of the same name in the Image_Display_Geometry class.

<pixel_latitude>

REQUIRED

Planetocentric latitude of the pixel projected onto the target, in the range ±90°

<pixel_longitude>

REQUIRED

Planetocentric longitude of the pixel projected onto the target, in the range 0-360°

<Footprint_Vertices>

OPTIONAL

If you have a series of pixel intercept points that define the footprint of the observation, use this wrapper class to list them. It contains a list of two or more <Pixel_Intercept> classes that should be filled out the same way as described above. You should list the pixels either in clockwise or counterclockwise sequence around the perimeter of the footprint, so that line segments drawn between succesive pixels (the last connecting back to the first) will produce the footprint on the image.

<Pixel_Intercept>

REQUIRED

You must have at least two occurrences of this class; you may have as many as needed to define the footprint.

Angles Included:

  • subsolar_azimuth
  • subsolar_latitude
  • subsolar_longitude
  • subspacecraft_azimuth
  • subspacecraft_latitude
  • subspacecraft_longitude

<Surface_Geometry_Min_Max>

OPTIONAL

This class lists min/max pairs of geometric angles calculated for the target surface. You must provide both minimum and maximum for any particular angle. If you have geometry for specific points rather than ranges, use the <Surface_Geometry_Specific> class to provide those values.

Angles Included:

  • minimum_latitude
  • maximum_latitude
  • minimum_longitude
  • maximum_longitude
  • minimum_subsolar_azimuth
  • maximum_subsolar_azimuth
  • minimum_subsolar_latitude
  • maximum_subsolar_latitude
  • minimum_subsolar_longitude
  • maximum_subsolar_longitude
  • minimum_subspacecraft_azimuth
  • maximum_subspacecraft_azimuth
  • minimum_subspacecraft_latitude
  • maximum_subspacecraft_latitude
  • minimum_subspacecraft_longitude
  • maximum_subspacecraft_longitude


<Surface_Geometry_Start_Stop>

OPTIONAL

If you have surface geometry calculated at the geometry_start and geometry_stop times included in this <Geometry_Orbiter> class, use this class to list the corresponding values. You must list these angles in start/stop pairs. If you have geometry for specific points rather than time ranges, use the <Surface_Geometry_Specific> class to provide those values.

<lat_long_description>

OPTIONAL

Note: This attribute is undefined and must have one of the values center, mean, or median.

Angles Included:

  • start_latitude
  • stop_latitude
  • start_longitude
  • stop_longitude
  • start_subsolar_azimuth
  • stop_subsolar_azimuth
  • start_subsolar_latitude
  • stop_subsolar_latitude
  • start_subsolar_longitude
  • stop_subsolar_longitude
  • start_subspacecraft_azimuth
  • stop_subspacecraft_azimuth
  • start_subspacecraft_latitude
  • stop_subspacecraft_latitude
  • start_subspacecraft_longitude
  • stop_subspacecraft_longitude


<Illumination_Geometry>

OPTIONAL

This class is a container for other classes used illumination angles of various types. These classes collect various named angles of interest either as single values, min/max ranges, or start/stop values. Angle names should be self-explanatory.

To avoid some tedious repetition, these class and attribute descriptions are somewhat abbreviated. In general, the containing class will be described briefly, attributes unique to each class will be described as usual, the individual angle attributes will merely be listed with abbreviated descriptions mainly concerning valid ranges where appropriate.

General Notes:

  • The container classes themselves may not be repeated.
  • All attributes are optional in their respective classes unless otherwise indicated; none may be repeated.
  • All angles require units of angle for each value. Typically all values will be given in units of degrees. For example:
     <emission_angles unit="deg">15.097</emission_angle>
     <start_solar_elongation unit="deg">17.9</start_solar_elongation>

<comment>

OPTIONAL

Here is a place to provide any additional explanatory text that might be apropos.

<Illumination_Specific>

OPTIONAL

This class provides illumination angles at a specific point in the image. This point must be specified in exactly one way: either through the reference_location attribute; the reference_pixel_location attribute; or the <Reference_Pixel> subclass.

Note: This constraint is not enforced. Type carefully.

<reference_location>

OPTIONAL

This defines a reference location in terms of some property of or point in the field of view. If present, this must have one of the following values:

  • Boresight Intercept Point
  • Constant
  • Subspacecraft Point
  • Target Center

<reference_pixel_location>

OPTIONAL

This defines a reference location in terms of a particular pixel location in the image when displayed according to the display settings established for this Geometry class. If present, it must have one of the following values:

  • Center
  • Lower Left Corner
  • Lower Right Corner
  • Upper Left Corner
  • Upper Right Cornet

<Reference_Pixel>

OPTIONAL

This class defines a reference location in terms of pixel subscripts in the image array. It is filled out identically to the class of the same name in the Image_Display_Geometry class.

Angles Included:

At least one of these must be present.

  • emission_angle
  • incidence_angle
  • phase_angle
  • solar_elongation

<Illumination_Min_Max>

OPTIONAL

This class gives illumination angles as min/max ranges. You must supply these values in min/max pairs. If you have single values, use the <Illumination_Specific> class, above.

Angles Included:

  • minimum_emission_angle
  • maximum_emission_angle
  • minimum_incidence_angle
  • maximum_incidence_angle
  • minimum_phase_angle
  • maximum_phase_angle
  • minimum_solar_elongation
  • maximum_solar_elongation

<Illumination_Start_Stop>

OPTIONAL

This class lists illumination angles calculated for the corresponding geometry_start_time and geometry_stop_time of this <Geometry_Orbiter> class. You must provide start/stop time pairs for this class.

Angles Included:

  • start_emission_angle
  • stop_emission_angle
  • start_incidence_angle
  • stop_incidence_angle
  • start_phase_angle
  • stop_phase_angle
  • start_solar_elongation
  • stop_solar_elongation

<Vectors>

OPTIONAL

This class is a container for other classes used to define vectors for various positions and velocities of interest. Two of the optional subclasses collect vectors in specific coordinate systems types - Cartesian and Planetocentric. The third optional subclass provides a mechanism for defining position and velocity vectors outside those included in the first two classes. Unless otherwise stated, positions and velocities are measured center-to-center, and references to "target" and "central body" refer to the objects identified previously in this <Geometry_Orbiter> class.

To avoid a lot of tedious repetition, these class and attribute descriptions are somewhat abbreviated. In general, the containing class will be described briefly, and the individual vectors classes will merely be listed - their names being self-explanatory. All vectors of similar type (all Cartesian velocity vectors, for example) will have the same attribute content.

General Notes:

The various vectors in the Geometry Discipline dictionary are derived from common parent classes, providing consistent structure and terminology. The "specific' vectors listed below have been defined for the set of vectors that appear in the majority of orbiter/flyby data products. For these vectors the start and end points ("observer" and "target", in general terms) and coordinate system are part of the definition of the vector itself. You should use these specific vectors whenever they might reasonably apply, as they provide a common nomenclature for these values that users can key into across the archive. When you need to specify a vector for a quantity outside this standard set, use the generic vectors, which allow you to specify observer, target, and coordinate system.

The details of the structure of each family of vectors in the Geometry Discipline dictionary are summarized on the Filling Out the Geometry Vector Classes page.

Additional Notes:

Within each of the wrapper classes and unless otherwise noted:

  • All vectors are optional.
  • Vectors may be in any order (this is not the usual case for PDS4 label classes and attributes).

Note: Vectors can also be repeated an arbitrary number of times within their respective classes. This seems like a bad idea for the non-Generic classes.

=== <comment>

OPTIONAL

If there is any additional explanation needed or desired regarding the contents of the following classes, here's a place for it. Note that there are no comment fields in the individual wrapper classes

<Vectors_Cartesian_Specific>

OPTIONAL

If present, this class must contain at least one of the following vectors. The abbreviation "SSB" stands for Solar System Barycenter.

The Position vectors below are filled out as described for the Vector_Cartesian_Position_Generic class on the Filling Out the Geometry Vector Classes page on this wiki, with the exceptions noted for specific vectors vs. generic ones.

The Velocity vectors below are filled out as described for the Vector_Cartesian_Velocity_Generic class on the Filling Out the Geometry Vector Classes page on this wiki, with the exceptions noted for specific vectors vs. generic ones.

Vectors Included:

  • Vector_Cartesian_Position_Central_Body_To_Spacecraft
  • Vector_Cartesian_Position_Central_Body_To_Target
  • Vector_Cartesian_Position_Earth_To_Central_Body
  • Vector_Cartesian_Position_Earth_To_Spacecraft
  • Vector_Cartesian_Position_Earth_To_Target
  • Vector_Cartesian_Position_SSB_To_Central_Body
  • Vector_Cartesian_Position_SSB_To_Spacecraft
  • Vector_Cartesian_Position_SSB_To_Target
  • Vector_Cartesian_Position_Spacecraft_To_Target
  • Vector_Cartesian_Position_Sun_To_Central_Body
  • Vector_Cartesian_Position_Sun_To_Spacecraft
  • Vector_Cartesian_Position_Sun_To_Target
  • Vector_Cartesian_Velocity_Spacecraft_Relative_To_Central_Body
  • Vector_Cartesian_Velocity_Spacecraft_Relative_To_Earth
  • Vector_Cartesian_Velocity_Spacecraft_Relative_to_SSB
  • Vector_Cartesian_Velocity_Spacecraft_Relative_To_Sun
  • Vector_Cartesian_Velocity_Spacecraft_Relative_To_Target
  • Vector_Cartesian_Velocity_Target_Relative_To_Central_Body
  • Vector_Cartesian_Velocity_Target_Relative_To Earth
  • Vector_Cartesian_Velocity_Target_Relative_To_SSB
  • Vector_Cartesian_Velocity_Target_Relative_To_Spacecraft
  • Vector_Cartesian_Velocity_Target_Relative_To_Sun

<Vectors_Planetocentric_Specific>

OPTIONAL

If present, this class must contain at least one of the following vectors.

The Position vectors below are filled out as described for the Vector_Planetocentric_Position_Generic class on the Filling Out the Geometry Vector Classes page on this wiki, with the exceptions noted for specific vectors vs. generic ones.

The Velocity vectors below are filled out as described for the Vector_Planetocentric_Velocity_Generic class on the Filling Out the Geometry Vector Classes page on this wiki, with the exceptions noted for specific vectors vs. generic ones.

Vectors Included:

  • Vector_Planetocentric_Position_Central_Body_To_Spacecraft
  • Vector_Planetocentric_Position_Central_Body_To_Target
  • Vector_Planetocentric_Position_Spacecraft_To_Target
  • Vector_Planetocentric_Velocity_Spacecraft_Relative_To_Target
  • Vector_Planetocentric_Velocity_Target_Relative_To_Central_Body
  • Vector_Planetocentric_Velocity_Target_Relative_To_Spacecraft

<Generic_Vectors>

OPTIONAL

This class is used when the start point, end point, or both are not covered by the vectors of the preceding specific classes. Five generic vector types are provided. You may repeat these classes as needed for however many vectors you need to define.

The contents and procedures for filling out the generic vector classes are detailed on the Filling Out the Geometry Vector Classes page on this wiki.

Vectors Included:

  • Vector_Cartesian_Acceleration_Generic
  • Vector_Cartesian_Position_Generic
  • Vector_Cartesian_Velocity_Generic
  • Vector_Planetocentric_Position_Generic
  • Vector_Planetocentric_Velocity_Generic