Creating a map cache in Geoserver using third-party services

It all started with the fact that when developing geoportals using ArcGis, customers increasingly began to say something like: “We like everything, but we can do everything the same, but using open source software”, implying at the same time replacing the MSSQL + ArcGis bundle Server + ArcGis Javascript (Silverlight) Toolkit on Postgres (PostGis) + Geoserver + Openlayers.

Well, in general, you can understand them, because 1-2-3 million rubles change for 0 rubles. There was no particular problem in the majority, vector data is transferred either through SHP files, or through converters from MSSQL to PostGis (or simply via SQL queries). There is a question with raster data. For example, there is a well-traced, tuned and multi-level cache map of Russia. In ArcGis, it is stored either in a compact form (in the form of bundles understandable only by ArcGis format) or non-compact, that is, the map tiles are simply located in directories. Then I was delighted and thought that in the second case everything would be exactly simple. But no - the tiles are of course divided into levels, however, they have strange names and may lie in strange subfolders, and with the geo-referencing of this cache, just a disaster.

But then a very simple and quick solution came - scan your own service (since the service sends tiles to the clear URL of the form "... MapServer / tile / Z / Y / X" where Z is the level number, and X and Y are tiles numbers according to horizontals and verticals respectively). Now there is another question - how to put these linked tiles on the Geoserver? In Geoserver, for such purposes Image Pyramid Plugin is used , or rather not exactly for such - it is mainly used to simplify working with giant TIFF files, the gdal_retile script from the gdal package traverses the TIFF file and creates many small geolocated tiles at different levels, divided into folders with numbers of levels.
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That's all the original data. At first, I wrote the application in my native C #, but decided to follow the path of this OSS and rewrote it in Java, naturally putting the code on GitHub.

The main form is:



Everything is simple:
- Tile url pattern - the url pattern for the tile, where {2} is the position of the level number, {0} is the position of the tile number horizontally (X), {1} is vertically (Y).
- Max layer bounds - geolocation of the entire layer, i.e. where the countdown begins and ends
- Region layer bounds - geolocation of the desired region
- Levels: Start - the initial "lower" level, for example 4, End the final "upper", for example 0 (the whole map is in one tile)
-Tile size - the size of the tile, which gives the service
- Jpeg compression - if you want output tiff to use compression.
- Reference system WKT - text describing the coordinate system, examples of coordinate systems can be found here
- Path folder for output files

That's all - after writing these parameters, click run and download tiles.

You can download the program here (need Java)
INFA is here
The code is here

And now a small tutorial for those who did not understand, but it became interesting

1. Download and install Geoserver ;
2. Download and install the ImagePyramid plugin ;
3. Download , unpack and run the application;
4. Click the OSM Example button - the fields are automatically filled in for the OpenStreetMap tiles, the first 5 layers;
5. Select the folder where to create tiles;
6. After completion, open the geoserver and create a pyramid storage and layer;
7. Open the layer preview and enjoy;
8. All the same, but with pictures here .

PS There is a glitch with not square pyramids, that is, those whose base is not a square, but a rectangle (very often in the UK epsg: 4326). For all rectangular (EPSG: 3857 (90013), EPSG: 3395) starting with 0 it seems to work correctly (OSM, Google, Yandex). And remember about the license agreement services when using content. Do not break them.