What is the effect of DPI in TileInfo in ServiceImageTiledLayer?

NathanMellor — Sat, 11 Dec 2021 07:34:06 GMT

I have used code like this to create a tileinfo for my custom tiled layer:

static public double resolution(int zoom) {
    return INITIALRESOLUTION / Math.pow(2, zoom);
}
public static TileInfo CreateTileInfo(int minZoom, int maxZoom)
{
 int dpi = 96;
 ArrayList<LevelOfDetail> levels = new ArrayList<>();
 for (int i = minZoom; i <= maxZoom; i++)
 {
 double resolution = resolution(i);
 double scale = resolution * dpi * 39.37;
 LevelOfDetail l = new LevelOfDetail(i, resolution, scale);
 levels.add(l);
 }
 return new TileInfo(dpi, TileInfo.ImageFormat.PNG, levels, new Point(-20037508.342789244, 20037508.342789244, SpatialReferences.getWebMercator()), SpatialReferences.getWebMercator(), 256, 256);
}

Why did I choose 96 as the DPI? I don't know, except that it seems every ArcGIS server in existence uses 96 as its dpi.

Example:

World_Topo_Map (MapServer)

Tile Info:

Height: 256
Width: 256
DPI: 96
Levels of Detail: 24
- Level ID: 0 [ Start Tile, End Tile ]
  - Resolution: 156543.03392800014
  - Scale: 5.91657527591555E8
- Level ID: 1 [ Start Tile, End Tile ]
  - Resolution: 78271.51696399994
  - Scale: 2.95828763795777E8

and so on.

So far so good, but take a look at these that a user sent me.

On the left is a custom map view invented in house. On the right, one using ArcGIS Android SDK.

Both of them say 14, but it has a different meaning.

On the left, it is a one to one pixel ratio. 14 means LOD 14 of the tile server.

On the right, 14 actually means Scale of 1:36111.909643.

But you must be taking into account the dpi of 96 vs whatever the screen dpi is.

I theorized that if I set the dpi to exactly what the device dpi is - in my case 576, they would look the same.

I cannot make that work.

I do not think setting it to the screen dpi is best. But for some map sources, 96 may not be the optimal number, right?

topic What is the effect of DPI in TileInfo in ServiceImageTiledLayer? in ArcGIS Runtime SDK for Android Questions

What is the effect of DPI in TileInfo in ServiceImageTiledLayer?