DEMData
Contents
DEMData is a data structure for decoding, backfilling, and storing elevation data for processing in the hillshade shaders data can be populated either from a pngraw image tile or from serialized data sent back from a worker. When data is initially loaded from a image tile, we decode the pixel values using the appropriate decoding formula, but we store the elevation data as an Int32 value. we add 65536 (2^16) to eliminate negative values and enable the use of integer overflow when creating the texture used in the hillshadePrepare step.
DEMData also handles the backfilling of data from a tile’s neighboring tiles. This is necessary because we use a pixel’s 8 surrounding pixel values to compute the slope at that pixel, and we cannot accurately calculate the slope at pixels on a tile’s edge without backfilling from neighboring tiles.
Constructors
new DEMData()
new DEMData(
uid:string|number,data:ImageData|RGBAImage,encoding:DEMEncoding,redFactor:number,greenFactor:number,blueFactor:number,baseShift:number):DEMData
Constructs a DEMData object
Parameters
| Parameter | Type | Default value | Description |
|---|---|---|---|
uid
| string | number
| undefined
| the tile’s unique id |
data
| ImageData | RGBAImage
| undefined
| RGBAImage data has uniform 1px padding on all sides: square tile edge size defines stride // and dim is calculated as stride - 2. |
encoding
| DEMEncoding
| undefined
| the encoding type of the data |
redFactor
| number
| 1.0
| the red channel factor used to unpack the data, used for custom encoding only
|
greenFactor
| number
| 1.0
| the green channel factor used to unpack the data, used for custom encoding only
|
blueFactor
| number
| 1.0
| the blue channel factor used to unpack the data, used for custom encoding only
|
baseShift
| number
| 0.0
| the base shift used to unpack the data, used for custom encoding only
|