[NAME]
vdb_tool - perform a use-defined sequence of tasks

[SYNOPSIS]
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 |

[Supported file formats]

 | 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 |

[Terminology]

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.

[Stack-based string expressions]

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, "{\$x:++}" 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 {\$i:++} -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.

[Examples]

## 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)'
 ```

[AUTHOR]
This manual page was written by Mathieu Malaterre <malat@debian.org> for the
Debian GNU/Linux system (but may be used by others).