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This problem is known by various names such as:
- Ctrl-Space doesn’t do anything in Eclipse!
- Why can’t I get auto-complete to work properly in Eclipse?
- I’ve just set up a new University computer and things don’t work like they do on my laptop (maybe that one’s just me…)
It’s actually very simple to solve, but the problem is actually nothing to do with Eclipse. First of all, let’s see what the problem is:
You’ve just installed Eclipse, are starting to do some programming in it, and want to use the very handy auto-complete feature. So, you type part of a function name and press Ctrl-Space, waiting for the magic to work and the rest of the name to be automatically typed….but it doesn’t happen!
In the image above (which unfortunately doesn’t include the cursor) I had typed ST, and pressed Ctrl-Space to autocomplete it but nothing happened.
When trying to fix this myself, I went in to the Eclipse options (Windows->Preferences, then General->Keys) and tried to find the command for auto-complete. Helpfully, it’s not called autocomplete or anything like that – it’s called Content Assist. This showed me that, as I expected, Content Assist was assigned to Ctrl-Space:
So why wasn’t Eclipse picking this up? I tried setting the key for Content Assist manually, but when I deleted the text in the key binding box and pressed Ctrl-Space, it showed that only Ctrl registered – somehow the spacebar press was being ‘eaten up’ by something else. What could it be?
The simple answer is: the Windows language services utility – obvious really! This seems to be set by default (at least some of the time) to switch between languages by using Ctrl-Space. On my personal computer I only have one language set up (English (UK)), but on the university computers there are loads – French, German, Italian, Chinese (simplified) etc. You can find out what languages you have set up by going to Control Panel -> Region and Language -> Keyboards and Languages (tab) and then Change Keyboards (again, how obvious…). You’ll see a list of languages installed – remove any that you don’t want (click the language and then click the Remove button) until you only have the ones you want left. That fixed it for me, but you can also check the Advanced Key Settings tab to make sure that none of the keyboard shortcuts that are set include Ctrl-Space.
Once you’ve done that, Ctrl-Space should work nicely
When you try and reproject a dataset in ArcGIS (for example, by using the Project Raster tool) you will see a dialog a bit like the one below:
The highlighted field wants you to specific a Geographic Tranformation. Although it says that it is optional, it often isn’t (I think the optionality depends on the type of transformation you’re trying to do). I’ve often found that there are a number of items available in the dropdown box and I have absolutely no idea which one to choose!
For example, when converting from OSGB to WGS84 there are the following options:
How on earth should you choose one of these? Until now I had been choosing semi-randomly – picking one, seeing if the result looks good, if not then trying another. However, the other day I found out about a list of these transformations in the ArcGIS documentation – available to download from the ArcGIS documentation page. This document (available for each different version of ArcGIS) lists all of the transformations available in ArcGIS and their theoretical accuracy. So, for example, we can find out that OSGB_1936_To_WGS_1984_2 is meant to cover England only, and OSGB_1936_To_WGS_1984_4 is for Scotland. The accuracies seem to be around 20m for each transform, although OSGB_1936_To_WGS_1984_5 (for Wales) has an accuracy of 35m.
I can’t believe I’d never come across this resource before – it allows me to actually make intelligent decisions about which transformation to use. I’d strongly suggest you get familiar with this document.
(I’d like to thank the GIS.SE users who helped me with a question I asked related to this problem)
I often find myself using Julian days as a simple method to represent dates in my code. It’s nice and easy, because every day is simply an integer (the number of days since the beginning of the year) and any time during the day can be represented as a floating point number (the fraction of that day which has elapsed at that point). Furthermore, lots of satellite imagery is provided with the dates specified as Julian days – for example, MODIS data filenames include the year and then the Julian day.
It’s fairly easy to convert a standard date (eg. 24th March) to the Julian day in most programming languages (there will either be a library function to do it, or it’s fairly simple to write one yourself) – but it’s not that easy to do in your head. So, I have created a Julian Day calendar poster:
It’s a very simple table that lets you choose the month and day, and get the Julian Day number. Just make sure you remember the note at the top – add one to the number (after February) if it’s a leap year!
It’s available for download below:
If you are creating maps then for goodness sake
Use sensible colours!
I was helping some undergraduates with some work the other day, and they decided to use the following colour scheme for representing river depth:
- Deep water: Red
- Medium-depth water: Bright green
- Shallow water: Pink
- Deep water: Dark blue
- Medium-depth water: Medium-blue
- Shallow water: Light blue
Isn’t it hard work to come up with nice colour schemes for all of your maps? Nope not at all – ColorBrewer has done it already! If you haven’t used this website already I urge you to do so, it provides a number of carefully-chosen colour-schemes designed for various different purposes. For representing river depth you’d probably want to use one of the blue Sequential schemes, but there are also Diverging schemes for data that goes off in two directions, as well as schemes for representing Qualitative data (those that have no explicit ordering). What’s more you can tell it to only show schemes that are color-blind-friendly, photocopier-safe etc, and it’ll produce a preview for you with various map styles (labels, cities, coastlines etc). All in all it’s very impressive, and very useful.
Plugins and extensions are available for a number of pieces of software to allow ColorBrewer colours to be easily used. These include an ArcGIS plugin (see the bottom answer for how to install with ArcGIS 10), R package, Python module and IDL routines.