Specific Data Import

Import of several other types of data is not automatic and it requires human intervention.

Graphics Formats

Importing data from image formats such as PNG, TIFF, JPEG or BMP is similar to import from raw/unknown file formats, only simpler.

It is simpler because the file structure is known and the file format is automatically detected. Hence the file type does need to be selected explicitly. However, the data interpretation is still unknown and must be specified manually. The pixmap import dialogue therefore resembles the Information tab of raw data import, requiring you to set the physical dimensions and value scale.

Note the physical dimensions suggested there are not obtained from the file, they are simply the last values used. Some SPM data formats are based on an image format (typically, TIFF is used as the base) and contain the information about physical scales and units, albeit stored in a manufacturer-specific way. In this case a separate import module can be written for this particular format to load the files automatically with correctly scaled values.

See the reference section High-Depth Image Formats for the details of support for high-depth images and the possibility of using them for data representations.

For plain (non-SPM) images there is also an option to Just use pixels for the dimensions. This sets the physical dimensions equal to the pixel dimensions. They can be still adjusted later, for instance using Dimensions and Units.

Image stack as volume data

A multipage image (image stack) can be also imported as volume data instead of a heap of images. It is enabled by Import as volume data. This option currently exists only for multipage TIFFs.

The z coordinate in the imported data is simply the image number in the stack (starting from 0). Use volume data Dimensions and Units or Z Calibration function to set the physical scale and/or units of z.

Graph Curves

Simple two-column text files containing curve data can be imported as graph curves. In some cases, these files are recognized automatically. They can also be explicitly selected as ASCII graph curve files in the file open dialogue, causing the import module to try harder to load the file as a graph data.

The import dialogue shows a preview of the graph and permits to set the units and labels.

XYZ Data

Three-column text files containing XYZ data are imported by selecting the XYZ data files file type. Again, they can be recognized automatically but requesting this format explicitly makes the module to try harder to load the file as XYZ data.

The import dialogue displays the number of points and physical ranges of the data and permits setting the lateral and value units. The displayed ranges in physical units are updated according to the units you enter so you can immediately see if they they are correct.

Occasionally one can encounter image data are stored as XYZ data with completely regular lateral coordinates. Since they are still meant to be treated as image data, just in an odd format, the import module attempts to detect this situation. It then offers direct rendering to an image instead of importing the file as true XYZ data.

Nano Measuring Machine XYZ Data

The Nano Measuring Machine data are sets of often huge XYZ files that would be difficult, if even possible to handle normally in Gwyddion. Therefore, they are directly rasterised to an image upon import. Select the main description file (.dsc) to open the data file set and set the import parameters.

Usually, the vertical size should be chosen as the number of profiles (i.e. number of data files). However, a larger resolution can be also useful. If you enable the Identical measures checkbox then the imported image will have square pixels. Only one resolution can be then entered – the other one is determined automatically.

On 64bit systems, the import module can currently handle up to 232 points per channel while the total number of data values is not limited. Note that reading the data points can take considerable time. Select only channels you are actually interested in to speed up the import process.

Nanonis SXM Data

Nanonis uses a right-handed coordinate system and Gwyddion a left-handed system. Hence it is not possible to preserve simultaneously how images look visually and the absolute coordinates of images and their features – the latter is required for correct import of spectra.

The default behaviour was varying between versions. Since version 2.52 you can choose it by setting the value of /module/nanonis/preserve_coordinates in the settings:

  • False means images look the same, but vertical coordinates are flipped.
  • True means coordinates are correct, but images look flipped vertically.