| VDB_TOOL(1) | User Commands | VDB_TOOL(1) |
vdb_tool - perform a use-defined sequence of tasks
This command-line tool, dubbed vdb_tool, can combine any number of the of high-level tools available in openvdb/tools. For instance, it can convert a sequence of polygon meshes and particles to level sets, and perform a large number of operations on these level set surfaces. It can also generate adaptive polygon meshes from level sets, ray-trace images and export particles, meshes or VDBs to disk or even stream VDBs to STDOUT so other tools can render them (using pipelining). We denote the operations **actions**, and their arguments **options**. Any sequence of **actions** and their **options** can be exported and imported to configuration files, which allows convenient reuse. This command-line tool also supports a string-evaluation language that can be used to define procedural expressions for options of the actions. Currently the following list of actions are supported:
| Action | Description |
|-------|-------|
| **for/end** | Defines the scope of a for-loop with a range for a
loop-variable |
| **each/end** | Defines the scope of an each-loop with a list for a
loop-variable |
| **if/end** | If-statement used to enable/disable actions |
| **eval** | Evaluate an expression written in our Reverse Polish Notation
(see below) |
| **config** | Load a configuration file and add the actions for processing |
| **default** | Set default values used by all subsequent actions |
| **read** | Read mesh, points and level sets as obj, ply, abc, stl, pts, vdb
or nvdb files |
| **write** | Write a polygon mesh, points or level set as a obj, ply, stl,
abc or vdb file |
| **vdb2points** | Extracts points from a VDB grid |
| **mesh2ls** | Convert a polygon mesh to a narrow-band level set |
| **points2ls** | Convert points into a narrow-band level set |
| **points2vdb** | Converts points into a VDB PointDataGrid |
| **iso2ls** | Convert an iso-surface of a scalar field into a level set |
| **ls2fog** | Convert a level set into a fog volume |
| **segment** | Segment level set and float grids into its disconnected parts
|
| **sphere** | Create a narrow-band level set of a sphere |
| **platonic** | Create a narrow-band level set of a tetrahedron(4), cube(6),
octahedron(8), dodecahedron(12) or icosahedron(2) |
| **dilate** | Dilate a level set surface |
| **erode** | Erode a level set surface |
| **open** | Morphological opening of a level set surface |
| **close** | Morphological closing of a level set surface |
| **gauss** | Gaussian convolution of a level set surface, i.e. surface
smoothing |
| **mean** | Mean-value filtering of a level set surface |
| **median** | Median-value filtering of a level set surface |
| **union** | Union of two narrow-band level sets |
| **intersection** | Intersection of two narrow-band level sets |
| **difference** | Difference of two narrow-band level sets |
| **prune** | Prune the VDB tree of a narrow-band level set |
| **flood** | Signed flood-fill of a narrow-band level set |
| **cpt** | Closest point transform of a narrow-band level set |
| **grad**| Gradient vector of a scalar VDB |
| **curl** | Curl of a vector VDB |
| **div** | Compute the divergence of a vector VDB |
| **curvature** | Mean curvature of a scalar VDB |
| **length** | Compute the magnitude of a vector VDB |
| **min** | Composite two grid by means of min |
| **max** | Composite two grid by means of max |
| **sum** | Composite two grid by means of sum |
| **multires** | Compute multi-resolution grids |
| **enright** | Advects a level set in a periodic and divergence-free
velocity field. Primarily intended for benchmarks |
| **expand** | Expand the narrow band of a level set |
| **resample** | Re-sample a scalar VDB grid |
| **transform** | Apply affine transformations to VDB grids |
| **ls2mesh** | Convert a level set surface into an adaptive polygon mesh
surface |
| **clip** | Clips one VDB grid with another VDB grid or a bbox or frustum |
| **render**| Render and save an image of a level set or fog VDB |
| **clear** | Deletes cached VDB grids and geometry from memory |
| **print** | Print information about the cached geometries and VDBs |
This command-line tool can perform a use-defined, and possibly non-linear, sequence of high-level tasks available in openvdb. For instance, it can convert polygon meshes and particles to level sets, and subsequently perform a large number of operations on these level set surfaces. It can also generate adaptive polygon meshes from level sets, write them to disk and even render them to image files.
Version: 10.6.1 Surface points: vdb_tool -read points.[obj/ply/stl/pts] -points2ls d=256 r=2.0 w=3 -dilate r=2 -gauss i=1 w=1 -erode r=2 -ls2m a=0.25 -write output.[ply/obj/stl] Convert mesh: vdb_tool -read mesh.[ply/obj] -mesh2ls d=256 -write output.vdb config.txt Config example: vdb_tool -config config.txt
-clear Deletes geometry, VDB grids and local variables
-clip Clip a VDB grid against another grid, a bbox or frustum
-close Morphological closing, i.e. dilation followed by erosion, of level
-config,-c Import and process one or more configuration files
-cpt Generate a vector grid with the closest-point-transform to a level
-curl Generate a vector grid with the curl of another vector grid
-curvature Generate scalar grid with the mean curvature of a level set surface
-debug Print debugging information to the terminal
-default Define default values to be used by subsequent actions
-difference CSG difference of two level sets surfaces
-dilate Erode level set surface by a fixed radius
-div Generate a scalar grid with the divergence of a vector grid
-each Start of each-loop over a user-defined loop variable and list of
-end Marks the end scope of "-for,-each,and -if" control actions
-enright Performs Enright advection benchmark test on a level set
-erode Erode level set surface by a fixed radius
-eval Evaluate string expression
-examples Print examples to the terminal and terminate
-expand Expand narrow band of level set
-flood Signed-flood filling of a level set VDB
-for Start of for-loop over a user-defined loop variable and range.
-gauss Gaussian convolution of a level set surface
-grad Generate a vector grid with the gradient of a scalar grid
-help,-h Print documentation for one, multiple or all available actions
-if Start of if-scope. If the value of its option, named test, evaluates
-intersection CSG intersection of two level sets surfaces
-iso2ls,-i2l Convert an iso-surface of a scalar field into a level set (i.e.
-length Generate a scalar grid with the magnitude of a vector grid
-ls2fog,-l2f Convert a level set VDB into a VDB with a fog volume, i.e. normalized
-ls2mesh,-l2m Convert a level set to an adaptive polygon mesh
-max Given grids A and B, compute max(a, b) per voxel
-mean Mean value filtering of a level set surface
-median Median value filtering of a level set surface
-mesh2ls,-m2ls Convert a polygon mesh into a narrow-band level set, i.e. a narrow-band
-min Given grids A and B, compute min(a, b) per voxel
-multires Construct a LoD sequences of VDB trees with powers of two refinements
-open Morphological opening, i.e. erosion followed by dilation, of a level
-platonic Create a level set shape with the specified number of polygon faces
-points2ls,-p2l Convert geometry points into a narrow-band level set
-points2vdb,-p2v Encode geometry points into a VDB grid
-print,-p Prints information to the terminal about the current stack of VDB
-prune Prune away inactive values in a VDB grid
-quiet Disable printing to the terminal
-read,-i Read one or more geometry or VDB files from disk or STDIN.
-render Ray-tracing of level set surfaces and volume rendering of fog volumes
-resample Resample one VDB grid into another VDB grid or a transformation
-scatter Scatter point into the active values of an input VDB grid
-segment Segment an input VDB into a list if topologically disconnected VDB
-sphere Create a level set sphere, i.e. a narrow-band signed distance to
-sum Given grids A and B, compute sum(a, b) per voxel
-transform Apply affine transformations (uniform scale -> rotation -> translation)
-union CSG union of two level sets surfaces
-vdb2points,-v2p Extract points encoded in a VDB to points in a geometry format
-verbose Print timing information to the terminal
-version Write timing information to the terminal
-write,-o Write list of geometry, VDB or config files to disk or STDOUT
Note that actions always start with one or more "-", and (except for file names) its options always contain a "=" and an optional number of characters used for identification, e.g. "-erode r=2" is identical to "-erode radius=2.0" but "-erode rr=2" will produce an error since "rr" does not match the first two character of "radius". Also note that this tool maintains two lists of primitives, namely geometry (i.e. points and meshes) and level sets. They can be referenced with "geo=n" and "vdb=n" where the integer "n" refers to age (i.e stack index) of the primitive with "n=0" meaning most recent. E.g. -mesh2ls g=1" means convert the second to last geometry (here polygon mesh) to a level set. Likewise "-gauss v=0" means perform a gaussian filter on the most recent level set (default).
| Extension | Actions | Description |
|-------|-------|-------|
| vdb | read and write | OpenVDB sparse volume files with float, Vec3f and
points |
| obj | read and write | ASCII OBJ mesh files with triangle, quad or points |
| ply | read and write | Binary and ASCII PLY mesh files with triangle, quad
or points |
| stl | read and write | Binary STL mesh files with triangles |
| pts | read | ASCII PTS points files with one or more point clouds |
| abc | optional read and write | Alembic binary mesh files |
| nvdb| optional read and write | NanoVDB file with voxels or points |
| txt | read and write | ASCII configuration file for this tool |
| ppm | write | Binary PPM image file |
| png | optional write | Binary PNG image file |
| jpg | optional write | Binary JPEG image file |
| exr | optional write | Binary OpenEXR image file |
We introduce terms: **actions**, **options**, **expressions**, and **instructions**. Actions are high-level openvdb tools, which each have unique options, e.g. -mesh2ls geo=1 voxel=0.1, where "-mesh2ls" is an action with two options "geo" and "voxel". Expressions are strings of code with one or more low-level instructions in our stack-based programming language (see below). These expressions start with "{" and ends with "}", and ":" is used to separate values and instructions. E.g. {1:2:+} is an expression with two values (1 and 2) and one instruction "+", and it reduces to the string value "3". See section on the "Stack-based string expressions" below for more details.
Note that **actions** always start with one or more "-" and (except for file names) its associated **options** always contain a "=" and an optional number of leading characters used for identification, e.g. "-erode r=2" is identical to "-erode radius=2.0", but "-erode rr=2" will produce an error since "rr" does not match the first two characters of any option associated with the action "erode".
Note that this tool maintains two stacks of primitives, namely geometry (i.e. points and polygon meshes) and VDB volumes (that may contain voxels or points). They can be referenced respectively with "geo=n" and "vdb=n" where the integer "n" refers to "age" of the primitive, i.e. its order on the stack. That is, "n=0" means the most recently added primitive and "n=1" means the second primitive added to the internal stack. So, "-mesh2ls g=1" means convert the second to last geometry (here a polygon mesh) to a level set. If no other VDB grid exists this output level set can subsequently be referenced as "vdb=0". Thus, "-gauss v=0" means perform a gaussian filter on the most recently added level set VDB. By default the most recent geometry, i.e. "g=0, or most recent level set, i.e. "v=0", is selected for processing.
This tool supports its own light-weight stack-oriented programming language that is (very loosely) inspired by Forth. Specifically, it uses Reverse Polish Notation (RPN) to define instructions that are evaluated during paring of the command-line arguments (options to be precise). All such expressions start with the character "{", ends with "}", and arguments are separated by ":". Variables starting with " are substituted by its (previously) defined values, and variables starting with "@" are stored in memory. So, "{1:2:+:@x}" is conceptually equivalent to "x = 1 + 2". Conversely, "{:++}" is conceptually equivalent "2 + 1 = 3" since "x=2" was already saved to memory. This is especially useful in combination loops, e.g. "-quiet -for i=1,3,1 -eval {:++} -end" will print 2 and 3 to the terminal. Branching is also supported, e.g. "radius={$x:1:>:if(0.5:sin?0.3:cos)}" is conceptually equal to "if (x>1) radius=sin(0.5) else radius=cos(0.3)". See the root-searching example below or run vdb_tool -eval help="*" to see a list of all instructions currently supported by this scripting language. Note that since this language uses characters that are interpreted by most shells it is necessary to use single quotes around strings! This is of course not the case when using config files.
## Getting help on all actions and their options
```
vdb_tool -help
```
## Getting help on specific actions and their options
```
vdb_tool -help read write
```
## Getting help on all instructions
```
vdb_tool -eval help="*"
```
## Getting help on specific instructions
```
vdb_tool -eval help=if,switch
```
## Hello-world example Create a level set sphere and save it to a
file
```
vdb_tool -sphere -write sphere.vdb
``` ## Hello-world example with option Same example but with options to save
the file in half-float precision
```
vdb_tool -sphere -write bits=16 sphere.vdb
```
## Converting a mesh into a level set Convert a polygon mesh file
into a narrow-band level and save it to a file
```
vdb_tool -read mesh.obj -mesh2ls -write level_set.vdb
```
## Read multiple files Convert a polygon mesh file into a
narrow-band level with a transform that matches a reference vdb
```
vdb_tool -read mesh.obj,reference.vdb -mesh2ls vdb=0 -write level_set.vdb
```
## Convert a sequence of files Convert 5 polygon mesh files,
"mesh_00{1,2,3,4,5}.obj", into separate narrow-band levels and
save them to the files "level_set_0{1,2,3,4,5}.vdb". Note that the
value of loop variables is accessible with a preceding "$"
character and that the end of the for-loop (here 6) is exclusive.The
instruction "pad0" add zero-padding and takes two arguments, the
string to pad and the desired length after padding.
```
vdb_tool -for n=1,6 -read mesh_'{$n:3:pad0}'.obj -mesh2ls -write
level_set_'{$n:2:pad0}'.vdb -end
```
## Loop over specific files Convert 5 polygon mesh files,
"bunny.obj,teapot.ply,car.stl", into the Alembic files
"mesh_0{1,2,3,4,5}.vdb". Note that all loop variables have a
matching counter defined with a preceding "#" character.
```
vdb_tool -each file=bunny.obj,teapot.ply,car.stl -read '{$file}' -write
mesh_'{$#file:1:+:2:pad0}'.abc -end
```
## Define voxel size from a loop-variable Generate 5 sphere with
different voxel sizes and save them all into a single vdb file
```
vdb_tool -for v=0.01,0.06,0.01 -sphere voxel='{$v}' name=sphere_%v -end
-write vdb="*" spheres.vdb
```
## Specify which grids to write into a single file Generate 4
spheres named after their stack id, i.e. 3,2,1,0, and write only grid 0 and
2 to a file
```
vdb_tool -for i=0,5 -sphere name='{4:$i:-}' -end -write vdb=2,0 tmp.vdb
```
## Define options with simple math expression Read both a vdb and
mesh file and convert the mesh to a vdb with twice the voxel size of the
input vdb.
```
vdb_tool -read bunny.vdb dragon.ply -mesh2ls voxel='{0:voxelSize:2:*}' -print
```
## Define options with complex math expressions Generate spheres
that are rotating along a parametric circle
```
vdb_tool -for degree=0,360,10 -eval '{$degree:d2r:@radian}' -sphere
center='({$radian:cos},{$radian:sin},0)' name=sphere_'{$degree}' -end -write
vdb="*" spheres.vdb
```
## Meshing of particles Converts input points in the file
points.[obj|ply|abc|pts] to a level set, perform level set actions, and
written to it the file surface.vdb:
```
vdb_tool -read points.[obj|ply|abc|pts] -points2ls -dilate -gauss -erode
-write surface.vdb
```
## Changing global default options Example with many properties of
scalar and vector fields
```
vdb_tool -default keep=true -sphere -curvature -grad -curl -div -length v=1
-debug
```
## If-statement to isolate level sets Read multiple grids, and render only level set grids
```
vdb_tool -read boat_points.vdb -for v=0,'{gridCount}' -if '{$v:isLS}' -render
vdb='{$v}' -end -end
```
## Use shell-script to define list of files Find and render
thumbnails of all level sets in an entire directory structure
```
vdb_tool -each file=`find ~/dev/data -name '*.vdb'` -read '{$file}' -for
grid=0,'{gridCount}' -if '{$grid:isLS}' -render vdb='{$grid}'
thumbnail_'{$grid:gridName}'.ppm image=256x256 keep=1 -end -end -clear -end
``` Most of the arguments should be self-explanatory, but at least two
deserve an explanation: -render has the option keep=1 because otherwise
rendered grids are removed from the stack which invalidates {gridCount}, and
-clear is added to avoid accumulating all grids as multiple files are
loaded.
--- # Pipelining:
vdb_tool supports unix-style pipelining, which is especially useful for interactive viewing. Specifically, vdb_tool can read VDB grids from stdin or write VDB grid to stdout. Here are some examples:
## Redirection of stdout and stdin:
```
vdb_tool -sphere -o stdout.vdb > sphere.vdb
vdb_tool -i stdin.vdb -print < bunny.vdb
cat bunny.vdb | vdb_tool -i stdin.vdb -print
vdb_tool -sphere -o stdout.vdb | gzip > sphere.vdb.gz
gzip -dc sphere.vdb.gz | vdb_tool -i stdin.vdb -print
```
## Pipelining multiple instances of vdb_tool
```
vdb_tool -sphere -o stdout.vdb | vdb_tool -i stdin.vdb -dilate -o stdout.vdb
> sphere.vdb
``` or with explicit semantics
```
vdb_tool -sphere -o stdout.vdb | vdb_tool -i stdin.vdb -dilate -o stdout.vdb
> sphere.vdb
``` Note that the example above is slow due to serialization of the VDB grid.
```
vdb_tool -sphere -dilate -o stdout.vdb > sphere.vdb
``` or with explicit semantics
```
vdb_tool -sphere -dilate -o stdout.vdb > sphere.vdb
```
## Pipelining vdb_tool with vdb_view for interactive viewing
```
vdb_tool -sphere -dilate -o stdout.vdb | vdb_view
```
## View a sequence of scaling, rotating, and translated tetrahedra
```
vdb_tool -for t=0,6.28,0.2 -platonic f=4 -transform vdb=0
scale='{$t:sin:2:+}' rotate='(0,0,{$t})'
translate='({$t:cos:5:*},{$t:sin:5:*},0)' -end -o stdout.vdb | vdb_view
```
## View a sequence of spheres deformed in an analytical fluid
field
```
vdb_tool -sphere d=80 r=0.15 c=0.35,0.35,0.35 -for i=1,20 -enright dt=0.05
k=1 -end -o stdout.vdb | vdb_view
```
## View a sequence of octahedrons deformed in an analytical fluid
field
```
vdb_tool -platonic d=128 f=8 s=0.15 c=0.35,0.35,0.35 -for i=1,20 -enright
dt=0.05 k=1 -end -o stdout.vdb | vdb_view
```
## Production example of meshing of fluid particles Generate
adaptive meshes from a sequence of points files, points_0[200,299].vdb, and
use mesh_mask.obj to clip off boundaries. Points are first rasterized as
level set spheres, then dilates, filtered and eroded and finally meshed
using the mask.
```
vdb_tool -read mesh_mask.obj -mesh2ls voxel=0.1 width=3 -for n=200,300,1
-read points_{$n:4:pad0}.vdb -vdb2points -points2ls voxel=0.035 radius=2.142
width=3 -dilate radius=2.5 space=5 time=1 -gauss iter=2 space=5 time=1
size=1 -erode radius=2.5 space=5 time=1 -ls2mesh vdb=0 mask=1 adapt=0.005
-write mesh_{$n:4:pad0}.abc -end
```
## Production example with complex math Union 200 level set
spheres scattered in a spiral pattern and ray-trace them into an image
```
vdb_tool -for n=0,200,1 -eval '{$n:137.5:*:@deg}' -eval '{$deg:d2r:@radian}'
-eval '{$radian:cos:@x}' -eval '{$radian:sin:@y}' -eval '{$n:sqrt:@r}' -eval
'{$r:5:+:@r_sum}' -eval '{$r_sum:0.25:pow:@pow_r}' -sphere voxel=0.1
radius='{$pow_r:0.5:*}' center='({$r:$x:*},{$r:$y:*},0)' -if '{$n:0:>}'
-union -end -end -render spiral.ppm image=1024x1024 translate='(0,0,40)'
```
This manual page was written by Mathieu Malaterre <malat@debian.org> for the Debian GNU/Linux system (but may be used by others).
| May 2023 | vdb_tool 10.0.1 |