# How to use WriteVTK properly when saving continous simulation results?

**URL:** <https://discourse.julialang.org/t/how-to-use-writevtk-properly-when-saving-continous-simulation-results/109506>\
**Category:** Performance\
**Tags:** package, writevtk\
**Created:** [January 31, 2024, 9:50am UTC](https://discourse.julialang.org/t/how-to-use-writevtk-properly-when-saving-continous-simulation-results/109506 "2024-01-31T09:50:45Z")\
**Posts on this page:** 1\
**Showing post:** 8

<div class="post-metadata">

**Author:** ![Ahmed\_Salih](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ahmed_salih/32/206579_2.png) [@Ahmed\_Salih](https://discourse.julialang.org/u/Ahmed_Salih)\
**Post date:** [February 12, 2024, 6:16pm UTC](https://discourse.julialang.org/t/how-to-use-writevtk-properly-when-saving-continous-simulation-results/109506/8 "2024-02-12T18:16:21Z")

</div>

Hey!

Yes, I ended up getting it to work, I included an example script here, perhaps of interest:

> [@Help me optimize my special solution to save VTP (VTK) file?](https://discourse.julialang.org/t/help-me-optimize-my-special-solution-to-save-vtp-vtk-file/110064):
>
> Hello! Lately I’ve learned a lot from all of you guys on the forum on how to write performant code and reduce allocs/type instabilities, which has been really nice. I have a case where I want to save a lot of simulation date each N time steps, which is why I need my special solution instead of WriteVTK which is an absolutely beautiful library. The code I have right now as testing is included here: 
> 
> > **Summary**
> >
> > Current code, click to open #https://www.analytech-solutions.com/analytech-solutions/blo…

> **Summary**
>
> Same script
> 
> ```julia
> #https://www.analytech-solutions.com/analytech-solutions/blog/binary-io.html
> using XML
> using XML: Document, Declaration, Element, Text
> using StaticArrays
> 
> ### Functions=================================================
> # Function to create a DataArray element for VTK files
> function create_data_array_element(name::String, data::AbstractVector{T}, offset::Int) where T
> # Create the DataArray elements
> dataarray = Element("DataArray")
>     
> # Set attributes based on the input vector's type
> dataarray.attributes["type"] = string(eltype(first(data)))
> dataarray.attributes["Name"] = name  
> dataarray.attributes["NumberOfComponents"] = string(Int(sizeof(first(data))/sizeof(eltype(first(data)))))
> dataarray.attributes["format"] = "appended"
> dataarray.attributes["offset"] = string(offset)
> return dataarray
> end
> 
> ###===========================================================
> # Points = [SVector{3,Float64}(1,2,3), SVector{3,Float64}(4,5,6)]
> # Kernel = Float64.([100, 200]) 
> # KernelGradient = [SVector{3,Float64}(-1,1,0), SVector{3,Float64}(1,-1,0)]
> N = 6195
> Points = rand(SVector{3,Float64},N) * 10
> Kernel = rand(Float64,N) * 1000
> KernelGradient = rand(SVector{3,Float64},N) * 100
> 
> function PolyDataTemplate(filename::String, points, variable_names, args...)
> # Generate the XML document and then put in some fixed values
> xml_doc = Document(Declaration(version=1.0,encoding="utf-8"))
> vtk_file = Element("VTKFile")
> vtk_file.attributes["type"] = "PolyData"
> vtk_file.attributes["version"] = "1.0"
> vtk_file.attributes["byte_order"] = "LittleEndian"
> vtk_file.attributes["header_type"] = "UInt64"
> 
> # PolyData is the main section, filling it out
> polydata = Element("PolyData")
> piece = Element("Piece")
> N = length(points)
> piece.attributes["NumberOfPoints"] = string(N)
> 
> # This Points element and its associated DataArray has to be constructed individually
> points_element = Element("Points")
> point_dataarray = create_data_array_element("Points",points,0)
> point_dataarray["offset"] = 0
> 
>         
> # Generate appended data element
> appendeddata = Element("AppendedData")
> appendeddata.attributes["encoding"] = "raw"
> 
> # Start writing the file and generating the correct dataarrays with the right offsets in the loop
> NB = 0
> io = IOBuffer()
> write(io,"\n_")
> UncompressedHeaderN = N * length(first(points)) * sizeof(typeof(first(points)))
> NB += write(io, UncompressedHeaderN)
> NB += write(io, points)
> 
> # Generate XML tags for kwargs data
> pointdata = Element("PointData")
> dataarrays = Vector{XML.Node}(undef,length(args))
> 
> for i in eachindex(args)
> arg = args[i]
> dataarrays[i] = create_data_array_element(variable_names[i],arg,NB)
> 
> A = typeof(first(arg))
> T = eltype(A)
> Ni = length(arg)
> Tsz = sizeof(T)
> Nc = Int( sizeof(A) / Tsz )
> HowManyBytes = Tsz*Nc*Ni + Tsz
> 
> NB += HowManyBytes
> 
> write(io, NB)
> write(io, arg)
> end
> 
> # Take the result from the buffer, turn to string and write it
> v = take!(io)
> t = Text(String(v))
> write(io,"\n")
> push!(appendeddata,t)
> close(io)
> 
> # Glue all xml pieces together
> push!(xml_doc,vtk_file)
> push!(points_element,point_dataarray)
> push!(piece,points_element)
> push!(polydata,piece)
> push!(vtk_file,polydata)
> map(x -> push!(pointdata,x), dataarrays)
> push!(piece,pointdata)
> push!(vtk_file,appendeddata)
> 
> XML.write(filename,xml_doc)
> end
> 
> save_location = raw"E:\SPH\TestOfFile.vtp"
> 
> d = @report_opt target_modules=(@ __MODULE__ ,) PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
> println(d)
> 
> @profview PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
> 
> b = @benchmark PolyDataTemplate($save_location, $Points, $(["Kernel", "KernelGradient"]), $Kernel, $KernelGradient)
> display(b)
> 
> @code_warntype PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
> 
> PolyDataTemplate(save_location, Points, ["Kernel", "KernelGradient"], Kernel, KernelGradient)
> 
> ```

It is about 10% faster than WriteVTK, with same memory foot-print, but lot less flexibility etc. only this one format the way I want 🙂 I was not able to figure out how to nicely preallocate the whole file and buffer and then directly update the buffer to avoid allocs when using `XML.jl` so I took a break from it…

Let me know what you think, quite curious about your opinion

Kind regards

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