cache elevation data of world wind java using mapproxy

I finally find a way to cache the elevation data of world wind java with mapproxy.
Old version of mapproxy did not handle tiff 16bit, and mapproxy-1.11 with pillow-5.2 do.

Keypoints:
1. get elevation tiles in image/tiff
2. store the tiles in image/png, mode I
3. deliver the tiles in image/ppm

==mapproxy.yaml==
layers:
  - name: Elev
    title: NASA_SRTM30_900m_Tiled in TIFF
    sources: [Elev_cache]

caches:

  Elev_cache:

    sources: [Elev_wms]

    format: png16

    request_format: image/tiff

    grids: ['Elev_grid']

    image:

      resampling_method: bicubic

    cache:

       type: sqlite

       directory: /opt/mapproxy/cache/elev

sources:

   Elev_wms:

      type: wms

      supported_srs: ['EPSG:4326']

      wms_opts:

        version: 1.3.0

      req:

         url: https://worldwind26.arc.nasa.gov/elev

         layers: NASA_SRTM30_900m_Tiled

grids:

  Elev_grid:

    srs: EPSG:4326

    num_levels: 12

    origin: nw

globals:

  # image/transformation options

  image:

      paletted: False

      formats:

         png16:

            format: image/png

            mode: I

==end mapproxy.yaml==

And EarthElevations2.xml  can be used with the changes:

        <ImageFormat>image/ppm</ImageFormat>

        <DataType type="Int16" byteOrder="LittleEndian"/> 

        <FormatSuffix>.ppm</FormatSuffix>

NASA's servers with worldwindjava 1.5.1 on Linux

At least JDK-10.0.2 can communicate https servers of NASA, but older versions do not.
As far as I can see there are problems regarding SSL on older versions of JAVA.
If you are struggling with https connection, please try to use new versions.

Create a world file for PNG(, which shows the entire globe)

Unlike Geotiff, PNG does not have information about coordinates of a image file.
This leads little difficulty to create a map tile of world wind.

To overcome the difficulty, we need to create a world file (extention .pgw), and the contents can be calculated with the following site:
http://egb13.net/2009/03/worldfile-calculator/

In my case, I have a image which covers the entire globe generated by combining NASA's blue marble picture, and the input parameters are 90N 180W, 90S 180E, 83200x41600 pixels.

Putting the .pgw file, world wind imaginary and elevation installation program works, which I introduced in the past.

(Probably) The easiest way to get map tile for NASA's world wind with natural earth data

Converting from the natural earth data raster images to NASA's World Wind tile is a bit complicated.
I guess one of the easiest way is use the demo program in goworldwind.org.

How to:
(1) Get the script named "InstallImageryAndElevationsDemo" and launch it.
(2) "Install" the tiff image of the natural earth data.
(3) check the directory "c:\programdata\worldwindinstalled" on Windows.
      (Probably you can do the same thing on the other plat forms)

URL:
http://goworldwind.org/demos/