When you create a geometry cache, your cache is saved to disk as a .mc (Maya cache) file and an .xml description file is generated for your cache. The XML (eXtensible Markup Language) description file contains a list of important cache attributes that Maya uses to locate the data files for your geometry cached objects and other useful information like its cache’s time range. You can use the XML description file to keep track of your geometry cache files and their associated objects and scenes.
The geometry cache information contained in the XML description file is structured or organized by XML element and attribute. Each regular element (such as cacheType and Channel) or nested element (such as channel#) contains single or multiple attributes (such as Type, ChannelName, or SamplingRate) that list specific geometry cache properties.
Specifies the frame or time range of the geometry cache. For example, if a geometry cache contains an object’s deformations from frames 1-25, then the Range attribute would be 250-6250.
The time range is measured in time steps. Time steps are sub-frame units. Each geometry cache frame contains multiple time steps. The number of time steps contained in a frame is determined by your current Working Units (Time) user preference setting.
Number of time steps per frame = 6000/frame rate. For example, if your Working Units (Time) preference is set to Film (24 fps), then each of your geometry cache’s frames contains 250 time steps.
Specifies the following for the geometry cache:
Contains all object or channel-specific geometry cache information.
Each geometry cached object is assigned its own channel# nested element. For example, if you select 5 objects, set File Distribution to One File or One File Per Frame, and cache their deformations, then one XML description file would be generated and it would contain the following nested elements: channel0, channel1, channel2, channel3, and channel4. However, if you set File Distribution to One File Per Geometry, then one XML description file would be generated for each of the selected objects and only one channel# nested element would appear in each .xml file.
Specifies whether or not the channel’s deformation samples are saved to disk at equally spaced intervals. Regular indicates that the samples were saved at equally spaced intervals and Irregular indicates that the samples were saved at unequally spaced intervals.
These values are used by Maya to help it search for the channel’s geometry cache files on disk more efficiently.
Typically, the sampling type for a geometry cache is always Regular after creation. However, if you edit your cache in a way that changes its sampling interval, its sampling type will change to Irregular. For example, if your geometry cache evaluates every frame, and you append a cache to it that evaluates every 2 frames, then your cache’s sampling type would change to Irregular.
Specifies the spacing of the channel’s geometry cache files on disk when they were first created.
SamplingRate = Evaluate every frame(s) x Save every eval(s). For example, if you set Evaluate every frame(s) to 0.5 and Save every eval(s) to 1, and your user Working Units are set to 24 fps, then one sample would be taken and saved to your geometry cache every 125 time steps or half-frame.