support kosmtik

[matkoniecz]

https://github.com/kosmtik/kosmtik

[matkoniecz]

node index.js export --help:

Usage: node index.js export [project] [options]

project     Project to export.

Options:
   --mapnik-version             Optional mapnik reference version to be passed to Carto  [3.0.0]
   --proxy                      Optional proxy to use when doing http requests
   --keep-cache                 Do not flush cached metatiles on project load
   --renderer                   Specify a renderer by its name, carto is the default.  [carto]
   --localconfig                Path to local config file [Default: {projectpath}/localconfig.json|.js]
   --output PATH                Filepath to save in
   --width INT                  Width of the export  [1000]
   --height INT                 Height of the export  [1000]
   --bbox minX,minY,maxX,maxY   BBox to use [Default: project extent]
   --scale INT                  Scale the exported image  [1]
   --format FORMAT              Format of the export  [xml]

[matkoniecz]

How one may select zoom level for Kosmtik export? See https://github.com/kosmtik/kosmtik/issues/150 for search for z-level setter.

[nebulon42]

Kosmtik uses the node-mapnik implementation. I have started working on a node implementation of a mapdiff tool (independent of Kosmtik that also uses node-mapnik), but never finished it. Here is how I produced the zoom level images that I wanted:

var SphericalMercator = require('sphericalmercator');
...
var mercator = new SphericalMercator({
    size: self.size // this is the image size (one side of quadratic image)
});
...
var latLngToXY = function (lat, lng, z) {
    var n = Math.pow(2.0, z),
        latRad = lat / 180.0 * Math.PI,
        y = (1.0 - Math.log(Math.tan(latRad) + (1 / Math.cos(latRad))) / Math.PI) / 2.0 * n,
        x = ((lng + 180.0) / 360.0) * n;

    return [x, y];
};
...
var xy = latLngToXY(self.lat, self.lng, z);
map.zoomToBox(mercator.bbox(xy[0] - 0.5, xy[1] - 0.5, z, false, '900913'));

See also https://github.com/mapbox/node-sphericalmercator#bboxx-y-zoom-tms_style-srs.

self.lat and self.lng in combination with z represent the center coordinates and the zoom level of the image. Since the upper left corner is expected by node-mapnik I subtract 0.5 after the conversion to XY.

Maybe you can use a similar logic to produce the bounding boxes needed by Kosmtik.

[matkoniecz]

I am already doing something similar what is (hopefully) equivalent

    def self.get_render_bbox_size(zlevel, wanted_image_size, latitude)
      longitude_equator_rendered_length_in_pixels = 256 * 2**zlevel
      longitude_size = 360 * wanted_image_size.to_f / longitude_equator_rendered_length_in_pixels
      latitude_size = longitude_size * Math.cos(latitude * Math::PI / 180)
      return [latitude_size, longitude_size]
    end

The main problem will be for sythethic comparisons (stuff like https://cloud.githubusercontent.com/assets/899988/8719492/659a1770-2bac-11e5-8117-7156a0b89525.png - where each zoom level is using the same data, the same bbox, only different zoom level), but hopefully somewhere in Asia there is a large enough area without an unwanted coastline (currently I am rendering at [0, 20]).

[matkoniecz]

@nebulon42 - thanks for finding --bounds bug! It turned to be main obstacle, now things are starting to work correctly.