[MOAB-dev] Digging into ray_intersect_* in the OBBTreeTool - proposing an interface change
Grindeanu, Iulian R.
iulian at mcs.anl.gov
Wed Dec 14 10:08:48 CST 2016
Hello,
I am all for simplifying if possible.
It is clear that DagMC is the main user of this API, which works directly on a OBB tree.
The only other place we are using it is for EBMesher; there, we use both , ray_intersect_sets and ray_intersect_triangles on a obb tree.
For EBMesher, we actually fire only in 3 directions, but from many points, along a structured mesh; but it is important to retrieve all intersections, and it is important to understand what portion of the ray is inside/outside the "solid body geometry" we fire upon. A solid body is defined by its boundary shell (a brep).
EBMesher should actually work directly with iGeom, so it should not care about obb tree; EBMesher is not using iGeom, though, probably because it was too complex/unstable at that time:
/**\brief Intersect a ray with the model
*
* Intersect a ray with the model. Storage orders passed in should be a
* member of the iBase_StorageOrder enumeration.
* \param instance iGeom instance handle
* \param x Point from which ray is fired
* \param y Point from which ray is fired
* \param z Point from which ray is fired
* \param dir_x Direction in which ray is fired
* \param dir_y Direction in which ray is fired
* \param dir_z Direction in which ray is fired
* \param intersect_entity_handles Entities intersected by ray
* \param intersect_entity_handles_allocated Allocated size of
* intersections array
* \param intersect_entity_hangles_size Occupied size of intersections array
* \param storage_order Storage order of coordinates passed back
* \param intersect_coords Coordinates of intersections
* \param intersect_coords_allocated Allocated size of coordinates array
* \param intersect_coords_size Occupied size of coordinates array
* \param param_coords Distances along ray of intersections
* \param param_coords_allocated Allocated size of param_coords array
* \param param_coords_size Occupied size of param_coords array
* \param *err Pointer to error type returned from function
*/
void iGeom_getPntRayIntsct( iGeom_Instance instance,
double x,
double y,
double z,
double dir_x,
double dir_y,
double dir_z,
iBase_EntityHandle** intersect_entity_handles,
int* intersect_entity_handles_allocated,
int* intersect_entity_hangles_size,
int storage_order,
double** intersect_coords,
int* intersect_coords_allocated,
int* intersect_coords_size,
double** param_coords,
int* param_coords_allocated,
int* param_coords_size,
int* err );
Should we keep these APIs related ? They are doing about the same thing
iGeom is actually calling this, down deep:
return GeometryQueryTool::instance()->
fire_ray( nc_point, nc_direction, target_entities, ray_params, 0, EPSILON, &entities );
which is actually calling this (of GeometryQueryEngine)
// Do the ray fire. Note we will sort the hits by distance and append to the output lists.
if( gqe->fire_ray( origin, direction, tb_list, tmp_ray_params,
max_hits, ray_radius, tb_hit_list_ptr ) == CUBIT_FAILURE )
I don't want to complicate our lives, but should we look at these APIs for comparison?
Or maybe not....
In Meshkit, we need another "ray intersect capability" for the new implementation of an advancing front algorithm , done by Evan;
There, he is using cgm directly, with something like
RefFace* cgmFacePtr =
dynamic_cast<RefFace*>(reinterpret_cast<RefEntity*>(surface));
Surface* cgmSrfcPtr = cgmFacePtr->get_surface_ptr();
CubitStatus posDirResult = cgmSrfcPtr->closest_point_along_vector(
cvRayOrigin, cvRayDir, cvPointOnSrfc);
There, it is important to get just the first hit along the ray, to project a 2d mesh from working plane on a 3d surface (the working plane is relatively close to the 3d surface the mesh needs to be projected on)
Iulian
________________________________
From: moab-dev-bounces at mcs.anl.gov [moab-dev-bounces at mcs.anl.gov] on behalf of Paul Wilson [paul.wilson at wisc.edu]
Sent: Tuesday, December 13, 2016 11:18 AM
To: Vijay S. Mahadevan; Patrick Shriwise
Cc: moab-dev at mcs.anl.gov
Subject: Re: [MOAB-dev] Digging into ray_intersect_* in the OBBTreeTool - proposing an interface change
Hi Vijay,
On 12/13/2016 11:03 AM, Vijay S. Mahadevan wrote:
Paul, IMO, if there is DagMC specific logic embedded in general ray
intersection code, and if no one has complained about it so far, my
guess is there aren't many users relying on that API. In which case,
I'm all for simplifying it.
These methods would no longer return lists of intersections, but would return them one at a time for consideration by the calling application.
However, it is very unclear to me how a calling application would know
whether to stop querying again or if it should be satisfied once the
first successful entity is found. If there is a stronger reasoning for
this behavioral change, that would help motivate the change better.
But as I said above, if DagMC is the sole consumer of this API, do
modify it so that it is part of the next version.
Conceptually there is really no difference imposed by this change. The calling application will be asked to accept intersections one at a time rather than getting a list all at once. As it is, the calling application has to decide how to deal with that list (if it has more than one entry). The simplest approach is to just add them all to a list and end up with the same information as was originally available.
Perhaps the interface can offer both options:
1. methods that return complete lists with not opportunity for filtering/disambiguation and don't require a callback function
2. methods that return nothing but require a callback function to register each intersection as they arise
Paul
Vijay
On Tue, Dec 13, 2016 at 9:17 AM, Patrick Shriwise <shriwise at wisc.edu><mailto:shriwise at wisc.edu> wrote:
Hi all,
Having seen how many other ray tracing codes operate I think that these are
valuable changes to the OrientedBoxTreeTool which will allow it to be
extended to many other applications.
Pulling out these DAGMC-specific intersection disambiguation operations into
separate functions for filtering intersections will also allow them to be
applied in other ray tracing kernels (AdaptiveKDTree, etc.) if desired.
-Patrick
Patrick C. Shriwise
Research Fellow
University of Wisconsin - Madison
Engineering Research Building - Rm. 428
1500 Engineering Drive
Madison, WI 53706
(608) 446-8173
On 12/09/2016 04:44 PM, Paul Wilson wrote:
Hello all,
I have been spending a lot of quality time with the ray_intersect_* methods
of the OrientedBoxTreeTool over the last few weeks. I think I have
(re)learned all the subtleties of the additional code that exists in
RayIntersectSets::leaf() (invoked with API function ray_intersect_sets).
In general, these are all additional tests that make sense only in the
context of a call from DagMC:
is this facet in a list of previous facets intersected by this ray prior to
this call
is this facet in a list of previous facets (or their neighborhood)
encountered during this call
is this intersection a piercing or glancing intersection as defined by
notions of surface sense known to DagMC
There is then a complex logic related to how many intersections to keep
based on three quantities: two are a "window" in which the distance to
distance to intersection must fall and the third is a count of how many
intersections to keep.
The logic for ray_intersect_triangles() includes none of this. I was
contemplating an interface change to ray_intersect_triangles() that would
add enough information to include the same tests, and modularizing those
tests to reuse code in both places. However, (a) the interface for that
would be awkward and (b) it would be imposing DagMC conventions on even more
code.
Instead I propose the reduce the interface of all ray_intersect_* methods to
include only the following:
const EntityHandle root_set: points to the root of the OBB Tree
const double tolerance: for use in searching for intersections (largely
unused at the moment, I think)
const double ray_point[3]: starting point of ray
const double unit_vector[3]: direction of ray
std::pair<double*, double*> window: window to narrow search for interesting
intersections
std::pair<double*, double*> register_intersection(...): call back function
to perform application specific filtering/disambiguation of possible
intersection, returning an updated window
These methods would no longer return lists of intersections, but would
return them one at a time for consideration by the calling application.
Since this is such a major interface change, I thought I'd solicit feedback
before embarking upon it. It won't necessarily bee that much code change,
but who knows how it impacts other possible users of this code???
Paul
--
-- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ --
Paul P.H. Wilson
Grainger Professor of Nuclear Engineering
608-263-0807
paul.wilson at wisc.edu<mailto:paul.wilson at wisc.edu>
419 Engineering Research Bldg
1500 Engineering Dr, Madison, WI 53706
calendar: http://go.wisc.edu/pphw-cal
Computational Nuclear Engineering Research Group
cnerg.engr.wisc.edu
Faculty Director, Advanced Computing Initiative
aci.wisc.edu
--
-- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ --
Paul P.H. Wilson
Grainger Professor of Nuclear Engineering
608-263-0807
paul.wilson at wisc.edu<mailto:paul.wilson at wisc.edu>
419 Engineering Research Bldg
1500 Engineering Dr, Madison, WI 53706
calendar: http://go.wisc.edu/pphw-cal
Computational Nuclear Engineering Research Group
cnerg.engr.wisc.edu
Faculty Director, Advanced Computing Initiative
aci.wisc.edu
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