An “observation” catalog file defines observation times and footprint appearance for observations of a target taken by a sensor. This is an example of an observation catalog file for the CASSINI ISS NAC instrument imaging Saturn:
{
"version": "1.0",
"name": "Cosmographia CASSINI Example",
"items": [
{
"class": "observation",
"name": "CASSINI_ISS_NAC_OBSERVATION",
"startTime": "1997-10-15 09:26:08.390 UTC",
"endTime": "2015-08-01 01:58:52.000 UTC",
"center": "Saturn",
"trajectoryFrame": {
"type": "BodyFixed",
"body": "Saturn"
},
"bodyFrame": {
"type": "BodyFixed",
"body": "Saturn"
},
"geometry": {
"type": "Observations",
"sensor": "CAS_ISS_NAC",
"groups": [
{
"startTime": "2004-05-24 05:48:03.043 UTC",
"endTime": "2004-05-24 05:48:08.643 UTC",
"obsRate": 0
},
{
"startTime": "2004-05-24 05:53:03.069 UTC",
"endTime": "2004-05-24 05:53:05.669 UTC",
"obsRate": 0
}
],
"footprintColor": [
1,
0.5,
0
],
"footprintOpacity": 0.4,
"showResWithColor": false,
"sideDivisions": 125,
"alongTrackDivisions": 500,
"shadowVolumeScaleFactor": 1.75,
"fillInObservations": false
}
}
]
}
The version and name attributes set the catalog format/content version (must be “1.0”) and the internal name of the catalog file.
The class attribute sets the object class to “observation”.
The name attribute sets the name that will be used to identify the observation object within Cosmographia. Optionally the label attribute can be used to set the label that will be shown next to the observation footprints.
The startTime and endTime attributes set the The observation’s “lifetime” span within Cosmographia. These times are optional. For on-going missions either endTime or both startTime and endTime can be omitted. If these items are present, this time span is normally set to be the same as the sensor “lifetime” span defined in the corresponding sensor catalog file but it can also be made shorter if desired. Note, though, that this time span does not determine the actual times for which the observation footprints or swaths are computed. Instead the actual times are specified in the geometry groups blocks described below and the observation “lifetime” span defined here must be equal to or be wider than the time span of these actual observations.
The center attribute contains the Cosmographia name of the target body. It must be the same as the name of the target in the corresponding sensor catalog file.
The trajectoryFrame and bodyFrame properties, both of the BodyFixed type with the body set to the same value as the center, direct the program to show observation footprints at fixed locations on the target body’s surface.
The geometry property define which sensor is taking observations, observation times, and how the observation footprints are visualized.
The sensor is specified by giving its Cosmographia name in the sensor attribute.
The groups blocks define the start and stop times (startTime, endTime) and the observation rate (obsRate) for each observation in the series. The observation rate determines the rate, in seconds, at which footprints will be drawn between the start and stop times. Setting the observation rate to 0 will create a continuous swath rather than a series of footprints. Multiple actual observation time/rate triplets with distinct start/stop boundaries and the same or different rates can be specified within the group block.
The rest of the geometry property attributes determine the appearance of the footprints. For example the showResWithColor attribute determines whether the footprints are drawn in a single color or in different colors depending on the spacecraft altitude above or the sensor image resolution on the surface of the center body. If showResWithColor is set to false, the color set by the footprintColor attribute is used.
If showResWithColor is set to true, the colors set by the colorScheme attribute are used. If the SPICE instrument kernel (IK) defining the sensor parameters does not include the INS(sensor NAIF ID)_IFOV keyword for the sensor, then the colorScheme attribute assigns colors based on the spacecraft altitude given in meters. If the IK includes this keyword, then the colorScheme attribute assigns colors based on the size of a single pixel footprint on the surface, also given in meters. If the INS(sensor NAIF ID)_IFOV keyword is present in the IK, its value must be given in microradians.
For example, this colorScheme used together with an IK that does not include the INS(sensor NAIF ID)_IFOV keyword
"colorScheme" :
{
"type": "Custom",
"intervals": [
{
"color": [ 1, 0, 0 ],
"startValue": 200000
},
{
"color": [ 0, 1, 0 ],
"startValue": 250000
},
{
"color": [ 0, 0, 1 ],
"startValue": 300000
}
]
}
will cause footprints for observations taken at altitudes between 200 and 250 km be shown in red, between 250 and 300 km be shown in green, and above 300 km be shown in blue.
On the other hand, this colorScheme used together with an IK including the INS(sensor NAIF ID)_IFOV keyword
"colorScheme" :
{
"type": "Custom",
"intervals": [
{
"color": [ 1, 0, 0 ],
"startValue": 100
},
{
"color": [ 0, 1, 0 ],
"startValue": 200
},
{
"color": [ 0, 0, 1 ],
"startValue": 300
}
]
}
will cause footprints for observations with a single pixel size on the surface between 100 and 200 meters be shown in red, between 200 and 300 meters be shown in green, and greater than 300 meters be shown in blue.
A more detailed description of some of the parameters in this catalog file is provided in the “CATALOG FILE FOR DEFINING AN OBSERVATION” section of the Cosmographia-SPICE User’s Guide.
SPICE-enhanced Cosmographia User's Guide 