Here are some criteria to choose the best compression method for your GeoTIFFs.
Compression must be performed before importing the GeoTIFF to the CartoVista Server. CartoVista will keep the original compression method of your file.
Compression ratio
A good compression ratio reduces the size of the file on the server. LZW performs well in terms of compression ratio. Note that the use of Predictors 2 (Horizontal differencing) and 3 (Floating point prediction) can further improve the results when there is a spatial correlation in the pixel values
The Deflate method also performs well but is slower when writing the file.
Reading speed
Compression reduces the reading speed of the GeoTIFF on the map. The LZW method nevertheless offers good results, with Deflate slightly behind. The Packbits method offers very good results in terms of reading speed, but the compression ratio depends a lot on the type of data and can be inefficient in some cases.
Aerial image and GeoTIFF RGB
The recommended compression method for RGB images is JPEG, in the YCbCr colour space.
LZW, Deflate and Packbits are lossless compression methods, unlike JPEG.
Projection system
Like all geographic layers, GeoTIFFs can be reprojected in Spherical Mercator on import. For large files, we recommend reprojecting to Spherical Mercator before importing the file into CartoVista for faster import.
For more information :
- https://kokoalberti.com/articles/geotiff-compression-optimization-guide/
- http://blog.cleverelephant.ca/2015/02/geotiff-compression-for-dummies.html
ZSTD compression is not currently supported by CartoVista.