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= Implementation of GRASS GIS module for 3D raster flow line computation =


|| Title: || '''Implementation of GRASS GIS module for 3D raster flow line computation'''||

|| Student: || Anna Petrasova, [http://gis.ncsu.edu/osgeorel/ North Carolina State University, Open Source Geospatial Research and Education Laboratory]||

|| Organization: || [http://www.osgeo.org OSGeo - Open Source Geospatial Foundation]||

|| Mentors: || [http://www4.ncsu.edu/~hmitaso/ Helena Mitasova], [http://grasswiki.osgeo.org/wiki/User:Huhabla Sören Gebbert] ||

|| GSoC link: || [https://www.google-melange.com/gsoc/project/details/google/gsoc2014/eil8iath/5750085036015616 abstract] ||

== Abstract ==

GRASS GIS' capabilities of representing and processing data in 3D raster (voxel) format, are rare among other GIS software packages and open opportunities for new applications, especially in research. In this project I would like to extend the 3D raster handling capabilities by developing a module for computing 3D vector flow lines of a voxel representing trivariate continuous field. This new module, !r3.flow, will extend the functionality of module r.flow into the third dimension.

== Introduction ==

GRASS GIS' capabilities of representing and processing data in 3D raster (voxel) format, are rare among other GIS software packages and open opportunities for new applications, especially in research. In this project I would like to extend the 3D raster handling capabilities by developing a module for computing 3D vector flow lines of a voxel representing trivariate continuous field. This new module, !r3.flow, will extend the functionality of module r.flow into the third dimension.


== Background ==

Although GRASS GIS is mainly used for processing 2-dimensional data, it supports 3 dimensions in both vector and raster data representation. Several 3D raster modules are offered by GRASS GIS and are using its 3D raster library; these modules focus mainly on creating and managing voxel data, computing statistics and converting to different formats. However, there is not many modules which would make use of voxel data and which would help in their analysis. In 3D, we miss standard tools used for topographic analysis such as slope, aspect or flow lines. Today, the importance of such tools increases with the availability of new measurement methods producing multidimensional datasets, such as time-series of soil data, water temperature or salinity. Three-dimensional flow lines can help us study the dynamics of elevation time-series in a form of space-time cube voxel representation. The visualization of such flow lines together with isosurfaces and other geographic data can be done directly in GRASS GIS.


== The idea ==

New module !r3.flow will use the flow tracing algorithm based on vector-grid approach implemented in r.flow module. The input aspect maps, represented by horizontal and vertical aspect 3D raster maps will be computed by v.vol.rst module. Alternatively the input aspect maps can be replaced by computation of gradient direction internally. New module !r3.flow should offer similar functionality as r.flow does, including upslope/downslope flow lines computation, flow lines density voxel and specifying number of cells between flow lines.

== Project plan ==

|| date || proposed task ||
|| 2014-05-19 - 2014-05-23 (week 1) || Write pseudocode for flow lines implementation ||
|| 2014-05-26 - 2014-05-30 (week 2) || Implementing dummy module which would only read 3D raster and write any vector lines to be able to test results
|| 2014-06-02 - 2014-06-13 (week 3-4) || Implementing the actual algorithm
|| 2014-06-16 - 2014-06-20 (week 05) || More testing and fixing problems
|| 2014-06-23 - 2014-06-27 (week 06) || Implement skip parameter (skip voxels for creating flowlines)
|| June 23 || Mentors and students can begin submitting mid-term evaluations
|| June 27 || Mid-term evaluations deadline
|| 2014-06-30 - 2014-07-04 (week 07) || Implementing upslope/downslope calculation
|| 2014-07-07 - 2014-07-11 (week 08) || Implement flow line density 3D raster
|| 2014-07-14 - 2014-07-18 (week 09) || Implement internal aspect calculation 
|| 2014-07-21 - 2014-07-25 (week 10) || More testing and fixing unresolved issues
|| 2014-07-28 - 2014-08-08 (week 11-12) || Depending on situation, either continue with work on !r3.flow or start to work on related module !r3.slope.aspect which might not be finished within GSoC
|| 2014-08-11 - 2014-08-15 (week 13) || Write code documentation and manual page for !r3.flow
|| August 11 || Suggested 'pencils down' date. Take a week to scrub code, write tests, improve documentation, etc.
|| 2014-08-18 - 2014-08-22 (week 14) || Submit evaluation and code to Google
|| August 18 || Firm 'pencils down' date. Mentors, students and organization administrators can begin submitting final evaluations to Google.
|| August 22 || Final evaluation deadline
|| August 22 || Students can begin submitting required code samples to Google