Managing Hydrodynamic Models With PHP

Managing Hydrodynamic Models with PHP Sydney Open Source Developers’ Conference 3 rd December 2008

Talk Outline
PHP class library for spatial data manipulation
Windows environment tweaked to facilitate usage of the library from the command line
PHP used to manipulate flood
models and present results
MySQL table structure developed to store and manage model input and output
Visualisations of flood model results can be used to summarise large and complex data sets

PHP Class Library
Developed over the last 7 years as a problem solving tool
Used to manipulate, transform and analyse spatial data
Stores the data structures in a MySQL database
PHP provides the “glue” between numerous small command line utilities.
Used to produce visualisations of flood modelling results

PHP Environment
Windows network with 75 users
PHP class library must be available to approximately 6 users
Scripts developed to perform common file manipulation tasks
Single PHP installation on a network drive to ensure a uniform operating environment
All users have access to the same class libraries

Benefits/Disadvantages of using PHP/MySQL
Benefits
Rapid development time
Readily interacts with text files and MySQL
Open Source
Can generate images using GD extension
Disadvantages
Slow run times
Memory hungry
Frequent minor changes to PHP architecture
Lack of pre-existing geometry and meshing libraries
MySQL Spatial support not mature

Using PHP From the Command Line
Meshing class library has no GUI
Scripts run from the command line
Scripts can be run interactively (php –a)
Interactive use of PHP allows greater flexibility when composing scripts
Requires the user to be familiar with the classes and methods
Several network “tweaks” are rolled out in the login script to make command line use of PHP easier

“ Command Prompt Here”
1.Navigate in your Registry to
HKEY_LOCAL_MACHINE/Software/Classes/Folder/Shell
and create a key called "Command Prompt" without the quotes.
2. Set the default string to whatever text you want to appear in the right-click menu.
3.Create a new key within your newly created command prompt named "command," and set the default string to
cmd.exe /k pushd %1
4.The changes should take place immediately. Right click a folder and your new menu item should appear.

Example PHP Command Line Session

Example PHP Script

Flood Modelling Process

cli_progress_bar

Using class cli_progress_bar
<?
include "meshlab.php";
$numsteps=100000;
$c=new cli_progressbar(100000,”Testing the progress bar”);
for($i=1;$i<=100000;$i++){
$c->update($i);
}
$c->finish();
?>

Commonly Used Tools in %PATH%
PHP Library makes extensive use of the exec() command
Commonly used tools are kept in a network folder which is included in the users PATH variable
Allows small command line utilities to be accessible to the PHP script
Allows a modular approach to the software
Facilitates the use of custom written helper utilities

Flood Modelling Challenges
Numerous applications used during the modelling process
Each application uses a different file format for storing meshes/points/other spatial information
Large volumes of data generated during the process
Numerous file formats used throughout the process

Available Data
Airborne Laser Scanning (ALS)
ALS produces hundreds of millions of points that describe the terrain surface
Geo-rectified Air Photo
Subsidence predictions
Flood model output

Air Photo

Levels of Detail in Terrain Models

Initial 2D Finite Element Mesh

PHP Classes

PHP Library Input/Output Formats

Flood Modelling Process

2 Dimensional Hydrodynamic Models
We use a 2 dimensional finite element mesh to represent the floodplain
Balance between mesh accuracy and number of elements
Elements are only required where flooding occurs
Need to cull points that are above the flood level
Need to reduce the level of detail in the remaining points

Finite Element Mesh Generation
Require less than 50000 elements with current computing technology
Resulting mesh must accurately represent the hydrodynamic features of the terrain
Quadric Error Metrics used to reduce mesh from ~1million to ~50000 elements (QSlim Application)
Results in “variable density” mesh
Good technique because it preserves volume
Important because this relates to the hydraulic conveyance of the topography
qslim_example.bat 

Data Flow and Storage

Example PHP Script

Vector vs Raster
Vector
Irregularly spaced data
Eg: triangulated meshes
Finite element models
Triangulated laser scan data
Raster
Images
Heightfields

2D Interpolation

3D Interpolation

Vector to Raster Conversion Depth Animation

Rasterised Data
Triangulation across each triangle or element allows us to calculate the following values at each pixel
ground height
water surface elevation
water velocity
RGB colour
ground slope
Some of these values vary with time allowinf the visualisation to be animated

Raster Database Structure

Terrain Model Properties - Pixel 1207,535

Design Storm Flood Depths Depth Animation

Design Storm Velocities

2D Animation Example

Databases

Indexing Structures - Nodes

Indexing Structures - Elements

Indexing Structures

Indexing Structures - Edges

Indexing Structures - Fulledges

Cross Sections Through an Irregular Mesh

Selecting a cross section from the database
Use of the “fulledges” indexing structure allows more complex queries to be performed
For example the following query will pull out a cross section across the mesh along a particular “Y” value
SELECT stored_fulledges.meshID, stored_fulledges.element1, stored_fulledges.element2, stored_nodes.x, stored_nodes.y, stored_nodes.z, stored_nodes_1.x, stored_nodes_1.y, stored_nodes_1.z
FROM
(stored_fulledges LEFT JOIN stored_nodes FORCE INDEX (PRIMARY) ON stored_fulledges.node1 = stored_nodes.nodeID )
LEFT JOIN
stored_nodes AS stored_nodes_1 FORCE INDEX (PRIMARY) ON stored_fulledges.node2 = stored_nodes_1.nodeID
WHERE (
(stored_fulledges.meshID = $meshID) AND ( stored_nodes.y > $y ) AND ( stored_nodes_1.y < $y)
) OR (
(stored_fulledges.meshID = $meshID) AND (stored_nodes.y < $y) AND ( stored_nodes_1.y > $y)
)
ORDER BY stored_nodes.x, stored_nodes_1.x;

Levels of Detail

Area of Interest - 20000 Element Mesh

Comparison Through Cross Sections
Initial mesh approximately represents the terrain
More detail required for smaller channels

Comparison Through Cross Sections
Smaller mesh with 20000 elements much better represents the cross section
More detailed analysis of the flow is possible

Level of Detail in the Finite Element Mesh

Mesh Validation
3D visualisations can assist in validation of the model
Allows checking to ensure mesh has enough detail
Integrity of channels can be visually checked
Show qvis model (ground_points_20k.bat)

Mesh Generation Tradeoffs
Why would we need multiple models of the same region at different levels of detail?
Development time vs accuracy
Mesh detail vs accuracy
Model Run Time vs Number of Elements
Disk Storage
Consider the accuracy of input data

Other Applications
Level of detail terrain modelling can be used for many applications
Air modelling
Noise modelling
Identification of Vegetation communities
Visual impact studies
Landform analysis (e.g. slopes, x-sections)
Rainfall intensity (Animation ->)
…

Visualising Flood Model Output in 3D
Flood model output can be rendered in 3D using Povray open source rendering program
Time varying data can be animated
Visualising the data in 3 dimensions can summarise complex datasets
Model output can be more accessible in this format

Air Photo

RMA Mesh

Thematic Representation of Maximum Depth

Heightfield

Using Povray to Create a 3D Render

Air Photo

DTM – Ground Returns

DTM – Non-Ground Returns

100 Year ARI Depth at Time 79500 seconds

Heightfield

Flood Model Results Draped on Heightfield

Rainfall Intensity Animation

Links
View some of the animations from the presentation at the following URL:
http://au.youtube.com/view_play_list?p=B8514B561CF5E613
http://au.youtube.com/watch?v=Z76_Wbd2cj0

Managing Hydrodynamic Models With PHP

by Andrew Goodwin on Dec 07, 2008

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Managing Hydrodynamic Models With PHP — Presentation Transcript