FAQ/ Conversion from ASC format to importable NetCDF format¶

Technical Reference Input/Output function/ Terrain, roughness, and embankment import function/ NetCDF format How do I create an importable netCDF file?

response¶

There are several ways to create a netCDF.

How to convert a text file to netCDF format using a tool called ncgen.exe
How to export mesh data in ASC format using GIS software such as QGIS and netCDF format using programming languages such as PowerShell

Here we will talk about the second method. For the first method, please refer to this article.

Data such as topography, roughness, embankment, etc. are created using GIS software and created in ESRI ASC Raster format.
Here is some sample data: Save these files to your desktop.

substance Sample

Elevation data glev_asc.txt

Roughness data roughness_asc.txt

Embankment top data leveeHeight_asc.txt

Embankment flag data leveeFlag_asc.txt
Install PowerShell.
From the Microsoft Store, install PowerShell.
If you want to install without using the Microsoft Store, see Install PowerShell on Windows.
Install the netCDF library.
Get the netCDF4 64-bit version from the Installing and Using netCDF-C Libraries in Windows website of the official NetCDF website.
The latest version as of October 2021 is netCDF4.8.0-NC4-64.exe.
The following instructions assume that this version 4.8.0 is installed.
By defaultC:\Program Files\netCDF 4.8.0\, the netCDF library is installed.
Install the netCDF library for PowerShell.
Download NetcdfCs.dll and C:\Program Files\netCDF 4.8.0\bin copy it to .
If necessary, use the . NET 5.0. Install .NET on Windows

Create a PowerShell script. Here is a sample:

# 入力ファイル
$GlevAscFile = Get-Item "glev_asc.txt"
$roughnessAscFile = Get-Item "roughness_asc.txt"
$leveeHeightAscFile = Get-Item "leveeheight_asc.txt"
$leveeFlagAscFile = Get-Item "leveeflag_asc.txt"

# 出力ファイル
$ncFileName = Join-Path (Get-Location) "DiovistaDomainData.nc"

# dllファイル
$dllFileName = Get-Item "C:\Program Files\netCDF 4.8.0\bin\netcdfCs.dll"
[void]([System.Reflection.Assembly]::LoadFile($dllFileName))

# エラー時停止
$ErrorActionPreference = "Stop"

enum NcType {
    NC_BYTE = 1
    NC_SHORT = 3
    NC_INT = 4
}
class AscData {
    [System.IO.FileInfo]$file
    [int]$ncols
    [int]$nrows
    [double]$xllcorner
    [double]$yllcorner
    [double]$dx
    [double]$dy
    [double]$nodataValue
    [double[]] $data
    [int[]] $intData
    [int16[]] $shortData
    [byte[]] $byteData
    [int]$validMin
    [double]$scaleFactor

    # ctor
    AscData([System.IO.FileInfo]$file, [NcType]$ncType, [int]$validMin, [double]$scaleFactor) {
        $this.file = $file
        $this.validMin = $validMin
        $this.scaleFactor = $scaleFactor
        $scaleFactorInverse = 1.0 / $scaleFactor
        $headerLines = 7
        $lines = Get-Content -Encoding utf8 $this.file.FullName
        foreach ($headerLine in $lines[0..($headerLines - 1)]) {
            $header = $headerLine -split " +"
            if ($header[0] -like "NCOLS") {
                $this.ncols = $header[1]
            }
            elseif ($header[0] -like "NROWS") {
                $this.nrows = $header[1]
            }
            elseif ($header[0] -like "XLLCORNER") {
                $this.xllcorner = $header[1]
            }
            elseif ($header[0] -like "YLLCORNER") {
                $this.yllcorner = $header[1]
            }
            elseif ($header[0] -like "DX") {
                $this.dx = $header[1]
            }
            elseif ($header[0] -like "DY") {
                $this.dy = $header[1]
            }
            elseif ($header[0] -like "NODATA_VALUE") {
                $this.nodataValue = $header[1]
            }
            else {
                throw [System.Exception] (("{0}: found not supported header: {1}" -f $this.file, $header[0]))
            }
        }
        $this.DumpHeader()
        $this.data = New-Object double[] ($this.ncols * $this.nrows)
        for ($j = 0; $j -lt $this.nrows; $j++) {
            $ws = $lines[$j + $headerLines] -split " +"
            $i0 = $j * $this.ncols
            for ($i = 0; $i -lt $this.ncols; $i++) {
                $this.data[$i0 + $i] = $ws[$i]
            }
        }
        if ($ncType -eq [NcType]::NC_BYTE) {
            $this.byteData = New-Object byte[] ($this.ncols * $this.nrows)
            for ($k = 0; $k -lt $this.data.Length; $k++) {
                $value = $this.data[$k]
                if ($value -eq $this.nodataValue) {
                    $this.byteData[$k] = 0;
                } else {
                    $this.byteData[$k] = $value
                }
            }
        }
        elseif($ncType -eq [NcType]::NC_SHORT) {
            $this.shortData = New-Object int16[] ($this.ncols * $this.nrows)
            for ($k = 0; $k -lt $this.data.Length; $k++) {
                $value = $this.data[$k]
                if ($value -eq $this.nodataValue) {
                    $this.shortData[$k] = $validMin - 1;
                } else {
                    $this.shortData[$k] = [int16]($value * $scaleFactorInverse)
                }
            }
        }
        elseif($ncType -eq [NcType]::NC_INT) {
            $this.intData = New-Object int[] ($this.ncols * $this.nrows)
            for ($k = 0; $k -lt $this.data.Length; $k++) {
                $value = $this.data[$k]
                if ($value -eq $this.nodataValue) {
                    $this.intData[$k] = $validMin - 1;
                } else {
                    $this.intData[$k] = [int]($value * $scaleFactorInverse)
                }
            }
        }

    }
    [void] DumpHeader() {
        $message = "file: {0}`n" -f $this.file.FullName
        $message += "ncols: {0}`n" -f $this.ncols
        $message += "nrows: {0}`n" -f $this.nrows
        $message += "xllcorner: {0}`n" -f $this.xllcorner
        $message += "yllcorner: {0}`n" -f $this.yllcorner
        $message += "dx: {0}`n" -f $this.dx
        $message += "dy: {0}`n" -f $this.dy
        $message += "nodataValue: {0}`n" -f $this.nodataValue
        Write-Host $message
    }
}

# load asc files
$GlevAsc = New-Object AscData($GlevAscFile, [NcType]::NC_INT, -100000, 0.01)
$roughnessAsc = New-Object AscData($roughnessAscFile, [NcType]::NC_SHORT, 0, 0.001)
$leveeHeightAsc = New-Object AscData($leveeHeightAscFile, [NcType]::NC_INT, -100000, 0.01)
$leveeFlagAsc = New-Object AscData($leveeFlagAscFile, [NcType]::NC_BYTE, 0, 1.0)
$asc = $GlevAsc

# create netcdf file
$ncFile = New-Object netcdfCs.NcFile
if ((Test-Path $ncFileName) -eq $true) {
    Remove-Item $ncFileName
}
# Options(bool isNetCDF4, bool forceOverwrite, int compressionLevel
$ncOption = New-Object NetcdfCs.NcFile+Options($true, $true, 6)
$ncFile.Create($ncFileName, $ncOption)
Write-Host ("Create {0}" -f $ncFileName)

# global attributes
# 表 9(1)ファイル識別子
[void]$ncFile.AddAttribute("title", [netcdfCs.NcType]::NC_CHAR, "DioVISTA calculation domain data")
# 使用するnetcdf規約のバージョン（CF-1.6）
[void]$ncFile.AddAttribute("Conventions", [netcdfCs.NcType]::NC_CHAR, "CF-1.6")
# その他コメント
[void]$ncFile.AddAttribute("comment", [netcdfCs.NcType]::NC_CHAR, ("generated on {0} by netcdfPs1_Convert-From-Asc-To-DiovistaDomainNc.ps1" -f (Get-Date)))

# dimensions
$dimLon = $ncFile.AddDimension("lon", $asc.ncols)
$dimLat = $ncFile.AddDimension("lat", $asc.nrows)

# variables
$varLon = $ncFile.AddVariable("lon", [netcdfCs.NcType]::NC_SHORT, $dimLon.DimId)
[void]$varLon.AddAttribute("add_offset", [netcdfCs.NcType]::NC_DOUBLE, $asc.xllcorner + $asc.dx * 0.5)
[void]$varLon.AddAttribute("scale_factor", [netcdfCs.NcType]::NC_DOUBLE, $asc.dx)
[void]$varLon.AddAttribute("units", [netcdfCs.NcType]::NC_CHAR, "degrees_east")

$varLat = $ncFile.AddVariable("lat", [netcdfCs.NcType]::NC_SHORT, $dimLat.DimId)
[void]$varLat.AddAttribute("add_offset", [netcdfCs.NcType]::NC_DOUBLE, $asc.yllcorner + $asc.dy * 0.5)
[void]$varLat.AddAttribute("scale_factor", [netcdfCs.NcType]::NC_DOUBLE, $asc.dy)
[void]$varLat.AddAttribute("units", [netcdfCs.NcType]::NC_CHAR, "degrees_north")

$varGlev = $ncFile.AddVariable("glev", [netcdfCs.NcType]::NC_INT, ($dimLat.DimId, $dimLon.DimId))
[void]$varGlev.AddAttribute("valid_min", [netcdfCs.NcType]::NC_INT, [int]$GlevAsc.validMin)
[void]$varGlev.AddAttribute("scale_factor", [netcdfCs.NcType]::NC_DOUBLE, $GlevAsc.scaleFactor)
[void]$varGlev.AddAttribute("units", [netcdfCs.NcType]::NC_CHAR, "m")

$varRoughness = $ncFile.AddVariable("roughness", [netcdfCs.NcType]::NC_SHORT, ($dimLat.DimId, $dimLon.DimId))
[void]$varRoughness.AddAttribute("valid_min", [netcdfCs.NcType]::NC_SHORT, [int16]$roughnessAsc.validMin)
[void]$varRoughness.AddAttribute("scale_factor", [netcdfCs.NcType]::NC_DOUBLE, $roughnessAsc.scaleFactor)
[void]$varRoughness.AddAttribute("units", [netcdfCs.NcType]::NC_CHAR, "m^(-1/3).s")

$varLeveeHeight = $ncFile.AddVariable("leveeHeight", [netcdfCs.NcType]::NC_INT, ($dimLat.DimId, $dimLon.DimId))
[void]$varLeveeHeight.AddAttribute("valid_min", [netcdfCs.NcType]::NC_INT, [int]$leveeHeightAsc.validMin)
[void]$varLeveeHeight.AddAttribute("scale_factor", [netcdfCs.NcType]::NC_DOUBLE, $leveeHeightAsc.scaleFactor)
[void]$varLeveeHeight.AddAttribute("units", [netcdfCs.NcType]::NC_CHAR, "m")

$varLeveeFlag = $ncFile.AddVariable("leveeFlag", [netcdfCs.NcType]::NC_BYTE, ($dimLat.DimId, $dimLon.DimId))
[void]$varLeveeFlag.AddAttribute("flag_meanings", [netcdfCs.NcType]::NC_CHAR, "east north")
$flagMasks = New-Object byte[] (2)
$flagMasks[0] = 1
$flagMasks[1] = 2
[void]$varLeveeFlag.AddAttribute("flag_masks", [netcdfCs.NcType]::NC_BYTE, $flagMasks)

$ncFile.SaveDefinitions()
# Write-Host "Save Definitions"

# set variable data
# x
$shortData = New-Object int16[] $dimLon.Length
for ($i = 0; $i -lt $asc.ncols; $i++) {
    $shortData[$i] = $i
}
$varLon.Values = $shortData
$varLon.SaveData($ncFile.NcId)

# y
$shortData = New-Object int16[] $dimLat.Length
for ($j = 0; $j -lt $asc.nrows; $j++) {
    $shortData[$j] = $asc.nrows - 1 - $j
}
$varLat.Values = $shortData
$varLat.SaveData($ncFile.NcId)

# Glev
$varGlev.Values = $GlevAsc.intData
$varGlev.SaveData($ncFile.NcId)

# roughness
$varRoughness.Values = $roughnessAsc.shortData
$varRoughness.SaveData($ncFile.NcId)

# leveeheight
$varLeveeHeight.Values = $leveeheightAsc.intData
$varLeveeHeight.SaveData($ncFile.NcId)

# leveeheight
$varLeveeFlag.Values = $leveeflagAsc.byteData
$varLeveeFlag.SaveData($ncFile.NcId)

$ncFile.Close()
# Write-Host ("Close {0}" -f $ncFileName)

In lines 2~5, specify the file to be entered.
On line 8, specify the full path of the file to output. Here, DiovistaDomainData.nc we have set to output to the desktop.
On line 11, specify the path to the netCDF library for PowerShell that you installed in step 2. Here,"C:\Program Files\netCDF 4.8.0\bin\netcdfCs.dll" we specify .
Paste the script into a text editor and save it as a file name on your desktop netcdfPs1_Convert-From-Asc-To-DiovistaDomainNc.ps1 .

Run the script in PowerShell.
Press + R and type in the dialog that appears [Run] pwsh .
When PowerShell starts, copy and paste the following string to run it:
1 2 3
cd $env:USERPROFILE\Desktop Set-ExecutionPolicy RemoteSigned -Scope Process .\netcdfPs1_Convert-From-Asc-To-DiovistaDomainNc.ps1

is created on your desktop DiovistaDomainData.nc .

Bring the created netCDF into DioVISTA.
1. Launch DioVISTA.
2. Select Menu [file] > > [Create new from template] [Latitude and longitude coordinates] >.
3. Select Project > [Calculation area] > [Import from NetCDF] .
4. Specify for the file name of the dialog that appears DiovistaDomainData.nc .
  Specify a mesh size of 25 m.
5. Data has been ingested into DioVISTA.

Last update: 2023-03-20

substance	Sample
Elevation data	glev_asc.txt
Roughness data	roughness_asc.txt
Embankment top data	leveeHeight_asc.txt
Embankment flag data	leveeFlag_asc.txt