RAMFlowAcc
Properties
| Property | Characteristic | Dimension | Description |
|---|---|---|---|
| PixelType | compulsory, user-defined, default: float |
0 | The data type of the input image pixel. |
| Nodata | compulsory, user-defined, default: 0 |
1 | Nodata value |
| Algorithm | compulsory, user-defined, default: MFD |
0 | The flow accumulation algorithm {Dinf, MFD, MFDw}. |
| FlowExponent | optional, user-defined, default: 4 |
0 | Flow exponent for MFDw algorithm. |
| FlowLength | compulsory, user-defined, default: NO_FLOWLENGTH |
0 | Parameter that specifies whether flow length or flow accumulation (NO_FLOWLENGTH) is calculated. Either UPSTREAM or DOWNSTREAM must be selected for flow-length calculations. |
Supported Image & Pipeline Features
| Feature | Details | Comments |
|---|---|---|
| Image dimensions | 2D | |
| Multi-band images | no | |
| Pipeline role | process | |
| Sequential processing | no | |
| Parallel processing | no | |
| Number of inputs | 2 | Second input (FlowWeight, s. below) is optional |
| Number of outputs | 1 |
Inputs
| Name | Description | |
|---|---|---|
| DEM | required | A digital elevation model that represents the height of the land surface. |
| FlowWeight | optional | A weight surface representing the proportion of flow that is able to pass a given pixel downhill. |
Overview
The RAMFlowAcc component calculates flow accumulation (FlowLength=NO_FLOWLENGTH) or flow length (FlowLength=(DOWNSTREAM | UPSTREAM)) of individual pixels according to the specified (Algorithm). The output image units are given in pixels. Flow accumulation denotes the nubmer of pixels flowing into a given pixel (including the pixel itself). Flow length represents the DOWNSTREAM or UPSTREAM distance from the given pixel to the flow outlet or flow initiation point (local maximum) respectively.
Important: As indicated by its name, the RAMFlowAcc component does not support sequential processing of large images. Therefore, it can only be part of a non-streaming pipeline, i.e. a pipeline ending in a DataBuffer component or an ImageWriter component with its StreamingMethod set to NO_STREAMING.
Algorithm
Dinf- D-infinity flow accumulation algorithm (Tarboton 1997).MFD- Multiple flow accumulation algorithm (Quint et al. 1991).MFDw- Weighted multiple flow algorithm using the FlowExponent (Holmgren 1994).
References
Holmgeren P 1994. Multiple flow direction algorithms for runoff modelling in grid-based elevation models: an empirical evaluation. Hydrological Processes 8: 327-334. Paper
Tarboton DG 1997. A new method for the determination of flow directions and upslope areas in grid digital elevation models. Water Resources Research 33: 309-319. Paper
Quinn P, Beven K, Chevallier P, Planchon O 1991. The prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models. Hydrological Processes 5: 59-79. Paper