Prepare and update raster and grid layers

This page applies to customer sites: the organisation data portals on Team Cloud, Business Cloud, Enterprise plans. It explains how Koordinates reads raster (imagery) and grid (elevation or other values) files when you import or update them, and what to check when an import fails. For background, see Introducing raster data, Understanding grid data and GeoTIFF format.

Raster or grid: Koordinates decides on import

You don’t choose between raster and grid when you upload. For GeoTIFF files, Koordinates looks at the first band:

• If the first band is 8-bit (a byte band), the data is imported as a raster, an image.
• If it has any other data type, such as 16-bit integers or floating-point values, the data is imported as a grid, a set of cell values.

This matters for imagery. A 16-bit colour image is imported as a grid, not a raster, and looks like a grid in the map viewer. If you want it to be a raster, convert it to 8-bit in your GIS software before you upload it.

Some other formats, such as Erdas Imagine (.img) and KEA files, can also hold a raster attribute table. Those with a table of values are imported as a third type that Koordinates handles separately.

Note

You can’t update a raster with grid data, or a grid with raster data. The update fails because the data types are different. Import the new data as a new dataset, or convert it to the type of the existing dataset.

Prepare your files

Check these before you upload:

• The file is georeferenced. A plain image with no location can’t be imported. If Koordinates says a tile isn’t georeferenced, add the location information (for example, embed it in a GeoTIFF) and try again.

• Each file is a single image. Files with sub-datasets aren’t supported.

• You’ve named tiles uniquely. If you import several files as one dataset, every file name must be different, even if the files are in different folders. Koordinates tells you how many tiles have duplicate file names and gives an example.

• The tiles match each other. To import several files into one dataset, they must have:

  • the same format,
  • the same projection,
  • the same type of data (all raster, or all grid),
  • the same number of bands, with the same data type for each band, and
  • the same nodata value for each band.

  If they don’t, the import page lists the differences, for example Files have different numbers of bands, Files have different data types or Files have different nodata values. This often happens when most of a set of tiles has an alpha band and some don’t, or when a few tiles use a different nodata value. Fix the odd ones out and upload again, or import the different tiles as a separate dataset.

Bands, alpha and nodata

• RGB and alpha. Koordinates reads each band’s colour interpretation from the file. If the last band of a 2- or 4-band 8-bit image doesn’t say what it is, Koordinates samples it. If fewer than 10 per cent of its pixels have values between 2 and 253, it treats the band as an alpha (transparency) band. Otherwise it leaves the band as it is. A four-band image whose fourth band is near-infrared, an RGBN image, normally has a spread of values in that band, so it isn’t treated as alpha. To avoid guesswork, set the colour interpretation of every band in your file before you upload it.
• Nodata. Koordinates records each band’s nodata value. Cells that match it aren’t treated as data. Use one nodata value across all the tiles of a dataset. Grid layers have a nodata value rather than an alpha band. See GeoTIFF format for how nodata and alpha appear in exports.

How the data is stored

Koordinates converts each tile to a Cloud Optimized GeoTIFF with overviews and lossless compression. Photographic imagery uses a profile suited to photographs, and floating-point grids use one suited to continuous values. The stored size isn’t the same as the size of the file you uploaded.

Update a raster or grid layer

Update a raster or grid in the same way as any other dataset. See Update a dataset with new data.

1. Start the update from the new tiles, or from the dataset

   The new data must be the same type as the dataset (raster or grid).

2. Choose what happens to the existing tiles

   On the update page, under Data Source, choose either:

   • Keep existing layer tiles and append/replace new tiles. Tiles in the update are added or replace the matching old tiles. Other existing tiles stay.
   • Clear existing tiles and only use new tiles. The dataset contains only the tiles in the update. Use this when the new data is the complete set.

3. Select Update and Publish, or Update and Save Draft

   Save a draft first if you want to check the result before it’s public. See Manage data updates and QA using drafts.

If a tile in your update is identical to a tile Koordinates already stores for the dataset, with the same name, size and pixel data, it reuses the stored tile instead of storing it again.

When a raster or grid is updated, older versions of replaced tiles can remain in storage.

Scheduled updates

Scheduled updates are for vector and table datasets. A raster or grid dataset doesn’t get the Scheduled Updates option, so update it by hand when new tiles are available.

If an import or update fails

1. Read the errors on the import page or in the email. Messages about projections, bands, nodata values, duplicate file names and georeferencing tell you what to fix.
2. Open the file in your GIS software. Check its projection, band count, data type and nodata value.
3. Import a few tiles first. If a large import fails, import a small selection to find the file that causes the problem.
4. Contact support. Raise a ticket with the dataset name, the time of the import and the error message.