Dunstable Downs

Saturday, July 28, 2007 at 20:49:02

I’ve been carrying out the further testing to the kite rig at Dunstable Downs (Note: whilst Mastermap might be up-to-date, the Landranger maps displayed at Steremap most certainly aren’t!). This offers fantastic views out over the Vale of Aylesbury, is wonderfully windy and hosts the internationally famous Dunstable Kite Festival (which incidentally is TOMORROW). It’s well worth a visit and now has the new Chiltern Gateway visitor centre. Designed to be eco-friendly and blend in to the landscape, it offers fantastic views out across the Vale and sports a reasonable cafe/restaurant.

Open Office Footers

Monday, July 23, 2007 at 12:33:40

I’ve finally taken the plunge and am in the process of fully switching over to Open Office. I’ve been wanting to do this for a while, partly to move over to open source software and partly because of Portable Open Office.I had tried importing a few MS Word documents and whilst the text comes through OK, it is a little hit and miss with the layout. Anyway I took the time to actually convert some of my documents and all in all I like Open Office. It is moderately intuitive (and let’s face it, most “office” suites are largely similar in use), responsive and easy to use.

Inevitably there are many smaller differences between Open Office and MS Office. One of the problems I hit in Writer was making headers/footers different on the front page of a document. In MS Word there is a tick box when setting up the page that determines if the front page should be different. Not so in Open Office and it took a little while to find out the solution, although what it shows is that the design of Open Office is more natural and elegant than Word, not being hindered by a long culture of “bolting on” new functionality. In essence, anything to do with formatting comes under styles and isn’t deferred to a tick box on a setup page. Thus going in to “Styles and Formatting” (F11) allows you to change the footnote style on the first page. It’s a much better way of designing a document; just have to “unlearn” those MS Word “skills”!!

Continuous Rotation Servos

Friday, July 20, 2007 at 19:31:04

The rig designs I have used for flying my cameras (from kites), all use model aircraft servos (e.g. Hitec, Futaba) to drive the rotation (horizontally) of the vertically pointing camera. For photogrammetric applications, vertical photos are the only ones worth taking and therefore the vertical axis is the only one about which we need to move the camera.

This creates a problem because the servos are designed for model aircraft which require movement of up to ~90 degrees for controls such as the rudder and flaps. With rotation around the vertical axis, we ideally want continuous 360 degree rotation. So what do we do?? Well the e-magazine KAPER lists six different ways of achieving full 360 degree rotation. These employ both external modifications (gearing) and internal modifications (extra electrics). Probably the simplest, and most effective, modification is method 4 which involves opening up the servo and cutting away the bump stops and grinding off the top of the final drive gear (ideally using a Dremel).

The first rig we built uses this method, unfortunately minor fluctations in the RC transmitter means that the servo occasionally stutters or will rotate (“creep”) ever so slowly when its meant to be in a neutral position. James Gentles has produced a little bit of kit which solves this problem (and is sold at Brooxes and KAPShop). The digital Futaba RC controller I use allows micro-adjustments to the controls which actually stops creep entirely, so I didn’t need this solution.

However next on the shopping list is the Hitec HSR-1422CR which purports to allow continuous rotation out-of-the-box. It’s on order so it’ll be interesting to see if this solves the problem

Fisheye Panoramas Continued

Thursday, July 19, 2007 at 13:27:44

Pano1Well it’s been a month since my last blog on creating panoramas from fisheye lenses. I had said I would come back to using Hugin to create panoramas, it’s just taken longer than I thought!

Hugin has a set of tabs across the top for working with the current image. Many of the tabs we don’t need to use because we are not stitching photos together. When loading a fisheye image, much of the lens information is automatically entered straight from the EXIF data. So, in summary, load your image (Assistant tab) and apply the following settings:

Assistant: set “Lens Type” to Circular Fisheye
Images: set Yaw-90, Pitch-90, Roll-0
Camera and Lens: set “Lens Type” to Circular Fisheye and “Degrees of View” to 180
Crop: you need to draw a circular mask around the part of the circular photo (i.e. exclude the black surrounding frame). If you uncheck “Always centre” then you will be able to fine tine the position of the mask
Stitcher: set “Projection” to equirectangular, “Field of View” to 360 (horizontal) and 180 (vertical), select an appropriate image size and make sure the “Stich Engine” is Nona.
Hit the “Stitch Now” Button

The original image (of Carlos!) is above and the unstitched version below. I’ll have some kite shots next week.


Google Gears

Saturday, July 14, 2007 at 20:21:50

I’ve just been tinkering with Google Gears. OK, so it’s old (ish) news (a month is a long time in IT), but I’ve had other things to do. Anyway, Google Gears is the first step in offering online apps, offline. For example, Google offer a pretty reasonable RSS aggregator called Google Reader. After Google Gears is installed, navigating to the Reader page will bring up a dialogue asking if you want to run this locally. If you do, all the feeds are downloaded to your machine for use when you are offline.

It’s a simple idea that’s been knocking around for a while and is really just the gradual progression of web technologies (and something, I gather, that will be offered, as a joint development effort, in Firefox 3).

It works under IE and Firefox on Windows, Mac and Linux. Unfortunately it comes as part of an installer, which is a pain because I wanted it to work with Portable Firefox. After a quick search, all you have to do is ZIP up the extension files in “C:\Program Files\Google\GoogleGears\Firefox” and then rename it to XPI. Drag and drop this straight in to Firefox and it will work fine. Neat solution.

RS and ArcMap

Friday, July 13, 2007 at 04:48:44

I’ve been doing a little bit of training this week on using ArcGIS for simple image processing and, whilst ERDAS Imagine remains my staple (simply because I’m familiar with it), it’s quite beneficial to find new ways of accomplishing old tasks. Indeed I should acknowledge Paul Goldsmith, as many of the ideas here we drummed up between us (“Image processign the ArcGIS way”).

ArcGIS is a bit of a mixed bag when it comes to image processing. If you don’t have ArcToolbox (and therefore access to ARC/INFO) then there are quite a few limitations. None the less there is sufficient here to make it well worthwhile. We started out by downloading Landsat ETM+ bands 2, 3 and 4 from GLCF. These are predominantly GeoTIFFs with a single band per file. After downloading and uncompressing, they were converted to GRID files (and this is the best place to start as ArcGIS prefers to work this way).

If you want to display a false colour composite this is very quick and easily achieved through the image properties and symbology. Likewisem sub-setting an image is remarkably easy. Simply zoom your data frame to the extent of interest and export the layer of interest selecting the data frame extents as the bounding coordinates (and this has to be one of the simplest sub-setting routines I’ve come across).

The real power of working with imagery comes from using (the paid for) extension Spatial Analyst. This has a “Raster Calculator” option which allows you to perform a variety of operators on raster data. Importantly, this accesses the underlying ARC/INFO and uses it’s commands. It’s therefore well worthwhile in being familiar with commands in the GRID module of ARC/INFO and these can be viewed in the ArcDoc help system (NOT the help in ArcMap). Thus you can stack multiple layers in to a single file (MAKESTACK) or perform simple operations to calculate indices such as the NDVI. A word of caution; make sure you set the working directory (under Options in Spatial Analyst) to the same as the locaiton of your data.

ArcGIS is really very capable but much of the power is hidden and not obviously visible. With ArcGIS having such a large market share of the GIS arena, it’s well worthwhile knowing how to make use of software you already have.

KML Editors

Wednesday, July 11, 2007 at 08:05:14

I was needing to create some KML files recently so had a quick hunt around for easy ways of creating and editing them. And whilst I could obviously do this in Google Earth itself, I already had a list of co-ordinates that I simply wanted to convert. And, of course, if it’s simple and straightforward that makes life much easier. I quick hunt around found CSV2KML which is freeware and allows the conversion of a CSV file to KML (doh!). The nice thing with this is that any spreadsheet (or indeed text editor) can very simply create a CSV file. It’s a nice solution and very simple to implement.

If you want to start from scratch with detailed control over the KML file and how placemarks are viewed then Northgates KML Editor is a good option. Again it’s free and easy to use.

GIS Day Review

Tuesday, July 3, 2007 at 12:04:08

GIS Day Guest Speaker Vanessa LawrenceGIS Day proved to be a great success with somewhere around 60 students attending from a range of local schools. A brief summary of the day and some limited practical materials will shortly be available at the Centre for GIS.

I gave the introductory presentation (also available at the above link) which used a range of satellite imagery to explore the “ethos” of Geography:


We need to understand where events occur and Geography then explores why they occur. Business and government then take on the idea of so what to implement policies. Geography is therefore central to nearly everything everybody does!!

Ken and James gave the students a GIS taster through two practical sessions using ArcGIS, Google Earth and Google SketchUp. The students finally came back together for our discussion panel. It was great to be able to draw together a variety of people from different sectors and industries and I’d personally like to thank the Metropolitan Police, cadcorp, CACI, ERM and ESRI for making staff available. The panel was completed by Vanessa Lawrence (CEO and Director General of the OS) who helped provide a lively debate.

Vanessa completed the day with an excellent broad sweep of GIS and the GI industry with a focus upon how OS fits in to that. I found it interesting and learnt a thing or two about the OS (like they have a team of 30 to find out where things change in the UK. The so called Change Detection Team!)

So all in all a good day and we are looking forward to organising a similar event next year. If you are a teacher and would be interested in attending (with or without your students) then please get in touch.

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