What kind of data is called field or options??
I looked up dopfield help and I think field means property…? then what is option?
Is it literally Options sub-data under Position or Geometry??

Fields are what volumetric data in DOPs are called. In SOPs we refer to volumetric data as volumes or grids as well as vdb's. In DOPs we refer to volumetric data as fields. This is to keep things straight when discussion data inside Houdini. They are all volumes.

Optional data is just that. Optional data that is added to DOP simulation objects that can be used by the various solvers. Basic contains all the common data shared by most all simulation DOP objects including the record id. The Options data is added with specific DOPs then applied to the simulation objects. These are added by the solver designer/architect to satisfy the requirements of the solver. To set various values, states, etc. If you wish, you can dive inside any DOP that creates simulation objects to see how the data is constructed and added to the simulation objects via Apply Data DOPs. The sub-folder naming is based on convention. You can add your own custom sub-data in your own custom folder if you wish. It's all completely open ended.

For example, you have highlighted the Options sub-data for the Position data entry for an RBD simulation object. Lots of user set data such as density set to 1000 which can be adjusted on the RBD Object DOP. As well there is p for pivot, t for translate and vel for velocity. t and v will be updated as the simulation is run and will reflect the current state of the simulation object. So the solver updates this Position data.

You will find Basic and Options sub data entries for most data bound to simulation objects.

Thank you for explanation! But I still quite understand the terminology “field”.
I looked up dopfield command help and it says following. It treats position data as field even though position data is not volumetric.
so I thought position data could be called field as well…?


>Returns the value of a field as a float.
>`dopfield(dop, objectSpec, subDataName, recordType, recordNum, fieldName)`

>dopfield(“/obj/dopnet1”, “obj0”, “Position”, “Options”, 0, “ty”)
>Returns the y position of object obj0


If I want to use dopfield command, What kind of data can I pass to fieldName parameter?
and what are subDataName and recordType??

Arg… Terminology.

Yes a field is also a value record entry as it relates to the functions that can be used to read that value: dopfield(), dopallfields(), dopfieldname(), dopfields(), dopfieldtype(), dophassubdata(), dopnumfields(), dopnumobjects(), dopnumrecords(), etc…

dopfield() is used to fetch a value from a record entry.
The subDataName value is set to the path in the DOP spreadsheet to the record you wish to fetch.
recordType is the subfolder name containing the data.

If you go to the Houdini Textport, type in:

help dopfield

and you will get help for the function along with a few examples.

also type in the Textport:

help -k dop

and you will get a list of all the expression functions that contains the keyword dop.

Ok!
Thank you Jeff!