Some learnings

What is geologically-constrained inversion?

2009-12-02T11:10:00.005+11:00

One of the key challenges facing mineral explorers in recent times is that many of the rich mineral deposits that stick out of the ground have now been found. The booming world's population, and the rapid development of China, India, and other countries means that new mineral resources must continuously be found to replace existing supplies. Explorers need to search deeper to find undiscovered deposits, but less information is available to them about buried rocks and their likelihood of containing new ore deposits. They cannot easily be cracked with a hammer or peered at with a hand lens.

The most efficient approach for attempting to map buried rocks is to acquire gravity and magnetic data at the surface, or from aerial surveys, and interpret the data in the context of all the available geological data and observations. This can be achieved using geophysical inversion of the gravity and magnetic data, a process whereby a 3D model of subsurface rock properties is generated that explains the observed geophysical data. To ensure that this model is consistent with other geological data and observations, such as maps and drilling, geological information can be included in the inversion process in the form of geological constraints.

Geologically-constrained inversion is therefore the process of extracting a prediction of the subsurface properties needed to explain BOTH measured geophysical data and observed geological data.

My recently completed PhD thesis describes this process in detail, however, a new article in Geoscience Australia's AusGeo News titled "Reliable subsurface models for mineral exploration" (PDF) provides a nice overview of the approach and benefits of using geologically-constrained inversion.

Mountain Bike Tracks: Black Mountain Loop, Canberra

2009-09-13T16:33:00.006+10:00

Here is the first in what I hope will be a series of posts covering mountain bike tracks that I've ridden. Most of the tracks will be "close" to Canberra, but we'll see how far afield I venture!

I'll start with my favourite track; a favourite because it is closest to my house, has some great views of Canberra and the Brindabella Mountains, and has some fun but relatively tame hills and turns that a rank amateur like me can cut their teeth on.

Black Mountain loop
Length: 14.4 km
Time: 1-1.5 hours
Elevation gain: 400 m
Further details: Pedal Power ACT
This loop starts out the back of CSIRO's Black Mountain labs (public access is allowed), and works its way around the edge of Black Mountain. It includes an optional extension loop through Aranda (accessed by passing through a tunnel under the Caswell Drive). The bonus loop starts with the steepest climb of the ride but just beyond the Aranda summit the climb is well rewarded with beautiful views of the Brindabella Mountains and farmland to the west. It finishes by heading out to the northwest shore of Lake Burley Griffin and heading back to CSIRO/ANU/Civic as you please. It's rough firetrails all the way through the Black Mountain reserve, and then bike path tarmac along the lake's north shore.

&amp;lt;br&amp;gt; &amp;lt;a href="http://orerocks.customer.netspace.net.au/001_BlackMountainLoop.html"&amp;gt;Click here for the map&amp;lt;/a&amp;gt;&amp;lt;br&amp;gt;
Elevation profile:

For those who are interested, the tools I am currently using to prepare these images are:

GPS: Garmin eTrex Vista C, with handlebar mount, using Shonky Maps
Garmin MapSource to make the profile
GPS Visualizer to create the Google Map

Shortcut to paste plain text in MS Word

2009-05-07T08:58:00.000+10:00

A serious let down of MS Word is the hoops it makes you jump through to paste text from other documents, web pages, emails, or spreadhseets without bringing all the unwanted formatting accross. Just give me the plain text! I don't want to go through the awkward Paste Special dialog box everytime.

Thankfully a Lifehacker reader has posted an easy solution for use in Word 2007. It can be easily adapted for earlier versions, like Word 2003, as follows:

Go to Tools->Macro->Macros.

Enter PasteSpecial under the Macro name.

Click Create

Replace the contents of the code editor with the following text:
Sub PasteSpecial()
Selection.PasteSpecial DataType:=wdPasteText
End Sub

Hit Save and then close the editor.

From the Word menu bar go to Tools->Customize. On any tab hit the Keyboard button.

In the left hand list scroll to Macros. In the right hand list scroll to PasteSpecial. Assign a new keyboard shortcut key in the box below by pressing the desired combination. Ctrl+Shift+V is a good option to replace the existing shortcut to the default Paste Special dialog box (which you can still reach from the menu bar).

Easy peasy.

Finished my inversion PhD thesis

2008-11-01T10:50:00.000+11:00

Today I finalised my Ph.D. thesis,

Geologically-constrained UBC–GIF gravity and magnetic inversions with examples from the Agnew-Wiluna greenstone belt, Western Australia

having passed my oral thesis defense on October 24th. It has been a fairly grueling year, but I am very pleased with the result. The thesis abstract abstract is presented below and the full thesis is available here.

Geologically-constrained inversion of geophysical data is a powerful method for predicting geology beneath cover. The process seeks 3D physical property models that are consistent with the geology and explain measured geophysical responses. The recovered models can guide mineral explorers to prospective host rocks, structures, alteration and mineralisation. This thesis provides a comprehensive analysis of how the University of British Columbia Geophysical Inversion Facility (UBC–GIF) gravity and magnetic inversions can be applied to subsurface mapping and exploration by demonstrating the necessary approach, data types, and typical results.

The non-uniqueness of inversion demands that geological information be included. Commonly available geological data, including structural and physical property measurements, mapping, drilling, and 3D interpretations, can be translated into appropriate inversion constraints using tools developed herein. Surface information provides the greatest improvement in the reliability of recovered models; drilling information enhances resolution at depth. The process used to prepare inversions is as important as the geological constraints themselves. Use of a systematic workflow, as developed in this study, minimises any introduced ambiguity. Key steps include defining the problem, preparing the data, setting inversion parameters and developing geological constraints.

Once reliable physical property models are recovered they must be interpreted in a geological context. Where alteration and mineralisation occupy significant volumes, the mineralogy associated with the physical properties can be identified; otherwise a lithological classification of the properties can be applied. This approach is used to develop predictive 3D lithological maps from geologically-constrained gravity and magnetic inversions at several scales in the Agnew-Wiluna greenstone belt in Australia’s Yilgarn Craton. These maps indicate a spatial correlation between thick mafic-ultramafic rock packages and gold deposit locations, suggesting a shared structural control. The maps also identify structural geometries and relationships consistent with the published regional tectonic framework.

Geophysical inversion provides a framework into which geological and geophysical data sets can be integrated to produce a holistic prediction of the subsurface. The best possible result is one that cannot be dismissed as inconsistent with some piece of geological knowledge. Such a model can only be recovered by including all available geological knowledge using a consistent workflow process.

Over the next few months, I hope to post some of the key results here.

Slow Remote Desktop Connection?

2008-10-03T06:55:00.000+10:00

I have spent most of the last 9 months logged into my university PC from home using Microsoft's Remote Desktop Connection. It has been a life saver, but every now and then things go wrong. One of the most common problems I have is occasional days (such as today) where the connection speed is so ridiculously slow as to be unusable. This seriously hampers my productivity and I haven't been able to achieve much of anything over the last 4 hours.

The problem is not the internet connection at either end: running connection speed tests at both ends shows that both internet connections are normal and fast.

Doing a quick search on the web in frustration I just discovered a solution that seems to work. The details are discussed here, but it basically comes down to the new version of Remote Desktop Connection (6.0) using a feature called Receive Window Auto-Tuning. This sounds like a beneficial feature in general, but temporarily disabling this service speeds up the slow connection problem immediately. Here's how:

Disconnect from Remote Desktop.
Open an administrator command prompt and enter:
netsh interface tcp set global autotuninglevel=disabled
Reconnect Remote Desktop.

When you're finished with the connection you can turn it back on by reversing the command:
netsh interface tcp set global autotuninglevel=normal

Somewhat tedious, but only occasionally is my connection afflicted, so I can handle it to regain lost hours of productivity. [TMCnet]

Sites for sharing large files

2008-08-27T11:19:00.000+10:00

Ever needed to share a file too big for email but didn't know how? Well here's a nice roundup of 13 websites that specialise in sharing large files, with a summary of the features and limitations of each. They're especially useful for adhoc collaborative projects.

VoIP sucks

2008-08-23T05:09:00.000+10:00

So being a fan of new technology and harbouring an active and passionate resentment for all telecommunication companies (and that includes you Fido, Telstra, Rogers, Telus), I am very keen to make the switch to VoIP. Unfortunately the system still seems like a gimmick rather than a service and after several years of failed attempts, I am giving up. My main use for VoIP is international PC-to-landline phone connections (too few friends and relatives have active VoIP connections to make much use of free PC-to-PC calls), and I have never had a single successful and satisfying experience connecting to landlines.

In frustration, more due to the embarassment of repeated ugly conversations of "Hello? Hello? Can you hear me? How abou...garblegarblegarble" than the wasted money, I recently lodged a complaint with my current provider, Freshtel. They have not provided any solutions, but did provide some useful criteria for judging whether VoIP might work for your situation prior to you signing up. The criteria they gave me were:

Upload data rate > 128 kb/s & ping time < 200 m/s

The upload speed is obviously how quickly your computer can send your voice to the recipient, and the ping time indicates how long it takes the data packets to connect to the recipient (roughly).

An easy way to check whether you hit the mark is to go to one of the many speed testing websites such as SpeedTest, and run the free test. Although my speed and times are fine for my local server, it would seem the trick is to test your upload speed and ping time using a server near the person you wish to call. As most of my calls are from Vancouver to Melbourne, that was the clincher test for me (see result in the image). With a fast cable connection the data transmission speeds will never be a problem, but the ping time is the killer. It basically tells me that Freshtel is not entirely to blame, but that data transmission from Canada to Australia is just too slow, and most VoIP providers will struggle to provide quality service.

For the record, my ping times to North America, Japan, and parts of Europe are completely fine. I just won't be using VoIP for calls to Australia, New Zealand, SE Asia, Africa, or South America anytime soon. Guess I am stuck with my landline for a few more years.

The amazing invisible floating bookshelf

2008-05-25T04:45:00.000+10:00

How To Install Invisible Shelves

I love it! Haven't you always wanted one of these floating bookshelves. Imagine a whole wall of them...

And the video is just so lovably cheesy.

[via Lifehacker]

Gridding errors for potential field data

2008-05-23T08:03:00.000+10:00

I regularly have a need to grid gravity and magnetic geophysical data, but don't have much in the way of fancy software to do it, mainly an old version of ER Mapper (6.3) and MATLAB. Recently I made a comparison between the methods I available to me and got some surprising results.

I have an extremely irregularly spaced set of gravity data on a topographic surface. Data spacings range from 25 m to 10 km. I require a 400 m grid. I will do some processing later that will get rid of grid points that are located "far" from any original data points, so my primary criteria for a good grid is:

The grid patch near an observed data point reproduces that data point accurately

I judged this by interpolating the recovered grid at the original data points and calculating the difference between the original data points and the grid value at those points.

The grid patch near observed data points has a nice shape to it - no rips, tears, jumps, spikes, etc.

I judged this by looking at the grid image and seeing if I liked how it looked near data points.

The methods I tried were:

ER Mapper, minimum curvature gridding, with tension = 25 (ER Mapper default for potential field data).

The grid image had little bumps at each of the datapoints that were widely spaced (like tent poles holding up a tent). The average difference to the original data points was 0.26 mGal or 0.53%

ER Mapper, minimum curvature gridding, with tension = 15.

The grid image still had the little bumps at each of the datapoints, but not as badly as the example above. The average difference to the original data points was 0.25 mGal or 0.51%.

MATLAB - GRIDDATA, 'v4' spline gridding.

The grid image looked nice and smooth where data were sparse, and detailed where data was abundant. The average difference to the original data points was 0.17 mGal or 0.34%.

MATLAB - GRIDDATA, 'cubic' gridding.

The grid image looked okay, but in some places there were sharp facets or triangles in the grid where data were sparse. The average difference to the original data points was 0.18 mGal or 0.37%.

This is hardly a robust analysis of gridding methods, and doesn't take into account all the multitude of algorithms out there, but it is enough to tell me that MATLAB's griddata command using 'v4' splines is more than acceptable for these problems (even if there are complaints about how inefficient and unreliable GRIDDATA it is). It will be my method of choice until I find a better one.

But it also gives a good indication of how poor all of these methods are at creating reliable grids. The errors of > 0.17 mGal are much greater than the measurement accuracy (including all sources of error) of < 0.05-0.10 mGal. User beware!

Sources of LEGAL free music

2008-04-29T02:43:00.000+10:00

I love music, and I love finding new music, and I love it even more when that new music is free. Here are the reliable places I know for getting free music online. In all cases the sites promise themselves to be legal and safe, but I make no assurances that they live up to their promises.

Internet Audio Archive (This site has several parts):

Live Music Archive: Here are fan recordings of a huge number of artists, many famous, many obscure, posted with authorisation from the artists themselves. The quality varies. Some are recorded with hand held audio recorders and capture more crowd noise than music. Others are recorded directly from the sound board and sound terrific. Spend some time browsing. (Some of the bands I like that are listed are: The John Butler Trio, Jack Johnson, Big Head Todd and The Monsters, Cowboy Junkies, Ben Lee, Mogwai, Gomez,
State Radio, Godspeed You! Black Emperor, Tim Reynolds, G. Love & Special Sauce, Explosions in the Sky, ...And You Will Know Us by the Trail of Dead, Michael Franti & Spearhead, ...)
Open Source Audio: These are freely licensed tracks provided by the community. I haven't figured out the best way to find things there yet, but there is plenty available. Some record labels make demo compilations or samplers available (sometimes including artwork). I particularly enjoy the Clan Analogue Sampled Synthesis electronica compilations.

Sweet Smelling Surfaces

This is an online electronica (ambient, minimal, and techno) label that has more than 50 electronica E.P.s available for free download, with high res album artwork. I don't know what they gain, but many of the artists have now become favourites of mine so I thought I'd spread the word.

Myuzyk

Another online electronica label with some neat "inspired by..." compilations, among others, available as 320 kbps MP3 and FLAC audio files.

Last.fm

Predominantly a streaming music site, many artists use it as a forum for posting free full-length demo tracks. For a recent listing of all such tracks visit Last.fm's free music chart or members' journals here or here.

South by Southwest Music Festival (SXSW)

Every year the massive SXSW music festival in Austin, Texas releases a bitTorrent containing >700 free mp3s showcasing the current year's performers. The music is voluntarily and freely supplied by the performers, and includes 1-2 tracks from many of the artists attending. The torrents are up to 2.5GB each, so you'll need some bandwidth, but there are many gems and your bound to find artists you know or like. You can get all the torrents from Greg Hewgill, or visit SXSW 2008, SXSW 2007, SXSW 2006. [via Lifehacker]

Using iTunes and Picasa with multiple users

2008-04-26T16:49:00.000+10:00

Recently I got a new Vista laptop and needed to transfer Picasa photo albums and iTunes music libraries from an XP laptop to the Vista laptop. iTunes, easy. Picasa, nightmare.

(Tip: I won't go into detail, the memories are too painful, but here's an overview. Since Vista and XP use different Document folder locations, first copy the Picasa data folders from XP:

C:\Documents and Settings\username\Local Settings\Application Data\Google\Picasa2

C:\Documents and Settings\username\Local Settings\Application Data\Google\Picasa2Albums

to their new locations in Vista:

C:\Users\username\AppData\Local\Google\Picasa2

C:\Users\username\AppData\Local\Google\Picasa2Albums

Then use a global search and replace utility (such as
MB-Search&Replace) to replace all occurrences of C:\the directory of your photos on XP machine\ with C:\the directory of your photos on Vista machine\ in all files in those two directories. Then open Picasa and hope for the best!)

But once they were moved I took the opportunity to follow some advice to set up Picasa up to allow multiple users access to the same set of photos, albums and tags. It worked a treat! The instructions are super easy to follow and we've had no troubles since.

In case you are feeling inspired, Paraesthesia also provides instructions on how to set up iTunes for multiple users, but I haven't tried it.

Free apps I like

2008-04-26T05:11:00.000+10:00

Here are some of the most useful FREE applications I use. I'll update this as I find good ones.

General Utilities

CD/DVD burning, including ISO images: ImgBurn & InfraRecorder
Hard drive visual analyser: WinDirStat
Open a command prompt in any directory: Command window here @ MS XP Powertoys
Copy paths, names, and UNC from right click context menu: Ninotech Path Copy
Provide a shortcut key to switch windows between multiple monitors: JumpWin (although I hear UltraMon is good too it is not free; the free JumpWin does all I need. Don't forget to chuck it in your startup folder.)
File compression (including ZIP): IZarc
Multiple file rename with wildcard search and replace: Rename Master
Duplicate file finder and remover: DupKiller

Music

Online music (including streaming): Last.fm (but the client is unreliable for scrobbling played tracks off iPods)
iPod audio scrobbling for Last.fm: LastPod

Photos/image/video software

Photo stitching - awesome, automatic, free, and developed at UBC: AutoStitch
Embed and edit tags in photos (including IPTC/XMP editing): iTag
Painting program: Paint.NET
Screen video capture: CamStudio
Photo editing: IrfanView
Convert any video to iPod format video: Videora
Play DVDs: Media Player Classic or VLC Media Player

Online apps

Online backups: Moxy
Desktop search: Google Desktop (without any gadgets thank you!)
Photo management: Google Picasa (please fix caption creation and editing, and make Albums more stable)
Online file conversion, including images, audio, video, documents and compressed files: Zamzar
Online secure and public file sharing/collaboration and syncing (replaces FTP transfers, file emailing, version control, and cumbersome manual syncing with memory sticks): Dropbox

Connectivity

Secure FTP Client: FileZilla
Telnet/SSH Client: PuTTy
Remote Unix virtual desktop: NoMachine NX Free Edition

Data tools

Data digitiser (for extracting data from printed graphs): Engauge Digitizer

Geophysics

Potential field FFT processing, including upward continuation: FourPot (by Markku Pirttijärvi at the University of Oulu, Finland)
Paleomagnetic analysis, including plotting NRM components: Paleomagnetic Analysis Program
2D gravity modelling and inversion: GravCadW
Hammer gravity terrain corrections: Hamxyz2
UBC-GIF inversion model builder and viewer: Meshtools3D

Programming

C/C++ development: Bloodshed Dev-C++

GIS

Google Earth (and don't forget the built in flight sim [Lifehacker]!)
Display ArcView shapefiles in Google Earth from ArcView with a click of a button: Do Google (an Avenue script)