GDAL_NODATA value being rounded

Generally the GDAL_NODATA metadata is working for me but I have some files that get an incorrect value.

For example with this file, when I run gdalinfo I get a nodata value of 9.99999998050644787e+18 but geotiff.js says 1.0E19 (gdalinfo is correct).

I’m not sure what the difference is with how gdalinfo determines the value, so I’m not sure if it’s possible that the nodata metadata is incorrect but gdalinfo gets its info from somewhere else, or if geotiff.js is not reading the value correctly.

$ gdalinfo example.tif

Driver: GTiff/GeoTIFF
Files: example.tif
Size is 279, 416
Coordinate System is:
GEOGCRS["WGS 84",
    DATUM["World Geodetic System 1984",
        ELLIPSOID["WGS 84",6378137,298.257223563,
            LENGTHUNIT["metre",1]]],
    PRIMEM["Greenwich",0,
        ANGLEUNIT["degree",0.0174532925199433]],
    CS[ellipsoidal,2],
        AXIS["geodetic latitude (Lat)",north,
            ORDER[1],
            ANGLEUNIT["degree",0.0174532925199433]],
        AXIS["geodetic longitude (Lon)",east,
            ORDER[2],
            ANGLEUNIT["degree",0.0174532925199433]],
    ID["EPSG",4326]]
Data axis to CRS axis mapping: 2,1
Origin = (135.033453258464164,-23.596259085710940)
Pixel Size = (0.003889256068923,-0.003789922154798)
Metadata:
  AREA_OR_POINT=Area
  TIFFTAG_RESOLUTIONUNIT=1 (unitless)
  TIFFTAG_XRESOLUTION=1
  TIFFTAG_YRESOLUTION=1
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  ( 135.0334533, -23.5962591) (135d 2' 0.43"E, 23d35'46.53"S)
Lower Left  ( 135.0334533, -25.1728667) (135d 2' 0.43"E, 25d10'22.32"S)
Upper Right ( 136.1185557, -23.5962591) (136d 7' 6.80"E, 23d35'46.53"S)
Lower Right ( 136.1185557, -25.1728667) (136d 7' 6.80"E, 25d10'22.32"S)
Center      ( 135.5760045, -24.3845629) (135d34'33.62"E, 24d23' 4.43"S)
Band 1 Block=272x416 Type=Float32, ColorInterp=Gray
  NoData Value=9.99999998050644787e+18

[zakjan]

I have a similar issue with CMEMS sea_ice_fraction scaled NetCDF. It contains non-sea points with descaled value 1.27999997138977, that I have to override as nodata.

gdal_translate -a_nodata 1.27999997138977 stores it as 1.27999997138977051 string. QGIS shows these points correctly as nodata. JS parses this string as 1.2799999713897705, so strict equality in JS doesn’t match the points.

My current workaround:

function maskData(data, nodata = undefined) {
  if (!nodata) {
    return data;
  }

  const maskedData = new data.constructor(Array.from(data).map(value => {
    return Math.abs(value - nodata) > Number.EPSILON * 2 ? value : NaN;
  }));

  return maskedData;
}

[zakjan]

I think my issue is similar to @DanielJDufour’s issue. As fileDirectory.GDAL_NODATA is stored as ASCII text, is it possible that it is a GDAL bug (or a “feature”)?