This category contains 7 posts

Google’s WebP vs JPEG: a more comprehensive test

My previous post was a bit unfortunate. The only relevant conclusion of it is that WebP does provide better compression ratios than JPEG for the same level of lossiness. Here is a new comparison method: Take the original image and compress it to WebP and JPEG using all possible quality levels. In both cases, the … Continue reading

Google’s WebP format compresses 6% better than JPEG

This is an attempt to quantify the compression performance of Google’s WebP image format compared to that of JPEG. The method is as follows: Take a large lossless image like this one and cut it up in a not too small number of large tiles. In my test, I have cropped the image a bit … Continue reading

On-the-fly reprojection of tiles using your favorite conventional WMS servers

If we accept Spherical Mercator tiles and the ZXY storage scheme as standard and still wish to use all the nice WMS servers we know, we can easily set up a middle tile server like this: For example, this request gets a OSM-like tile from a conventional Bavarian WMS server:,TK50&x=8711&y=5643&z=14 The advantage of this … Continue reading

JPG compresses better and uncompresses faster than ECW

The following comparison method has been applied to three lossless raster maps (urban orthophoto, rural orthophoto and a 8-bpp map): Compress the original image to JPG. Compress the original image to ECW using different compression levels until the resulting ECW file is slightly larger than the JPG file obtained in the previous step (this gives … Continue reading

Madrid 1656

The year 1656 saw the creation in Madrid of -at least- two graphic masterpieces: while Velázquez was doing that, the Portuguese cartographer Pedro Teixeira was doing this (click to enlarge): A superb map of Madrid in the times of the late Spanish Habsburgs. You can download it as a georeferenced (EPSG:25830) ECW file and also … Continue reading

Large shapefiles on small screens using a drawable spatial index

Sometimes a large vector layer needs to be rendered on a relatively small area on the screen. This happens especially with mobile devices, where screen size ranges between 240 x 320 and 480 x 850 pixels. If the vector layer affects a small number of pixels, it makes no sense to go through all the … Continue reading

Tile pyramids versus TIFF, ECW and such on mobile devices

Due to poor performance and portability issues associated with raster libraries, I don’t think it’s a good idea to use raster formats such as TIFF, ECW or MrSID on mobile devices such as (smart)phones, pocket PCs, tablets, etc. Google Maps, OpenLayers and OpenStreetMap have made quadtree tiles very popular. Initially intended to increase web mapping … Continue reading