Donald Noble’s Site

My job using only the 1000 most used words, as inspired by the excellent xkcd comic Up-Goer Five, the twitter hashtag #upgoerfive, and the up-goer five text editor

I plan power making houses. These use water from high ground that should run over the ground to lower down, but we build a wall to move the water into an under ground pass, which takes water to the power house. There it moves fast and turns a thing inside that makes power.

I work out how much power the power house will make. More water, or water higher up, gives more power. People want to buy the power for their lights, computer, TV, and to make their houses warm. If I know how much power we will have, and how much people want to buy the power for, I then know how much money the power house will make.

I also work out how much money is needed to build the power house, the turning thing that makes power, the wall in the water, and the under ground water pass. This has to be less than about ten times all the money the power house makes in a year, or it does not get built.

I draw pictures and write a story to tell people what the power house and wall will look like and where it will be. I have to think carefully about what people, trees, and animals (on the ground, in the water, and in the air) might not like about the power making house, and maybe change it to make it better. My work friends tell me what trees and animals are near, and which might not like the power making house the most. They draw pictures of where the trees and animals are.

We send the pictures and story to important people who decide if we can built the power making house or not. If they say yes, we draw more pictures to show people how to build the power house, wall in the water, and under ground water pass. These pictures are better and show the different parts drawn bigger, and they also show the parts inside the walls that hold them together.

In case you hadn’t worked it out, and didn’t know, I work on the design of hydro-electric power schemes.

When out on site visits for work (as with other times), I often record where I have gone using the GPS on my phone. It can often be handy to overlay this on a CAD drawing. Until now, converting this has been non-trivial. However, I now have a reasonable, if somewhat convoluted, workflow.

I record tracklogs using MotionX-GPS for the iPhone, which allows you to export the result as a gpx file containing Latitude/Longitude pairs in decimal degrees, with corresponding elevation and timestamp.

Using the free GPS Babel software, this can be converted to a csv comma delimited list of Latitude/Longitude pairs, although still in decimal degrees. However, for UK National Grid, they need to be in easting and northings from the origin off Cornwall.

This is where I had been getting slightly stuck. And I am sure there are various solutions using GIS software, but I wasn’t finding one, and don’t have easy access to GIS software anyway.

I was using an Excel spreadsheet developed for geocaching (Waypoint workbench) to convert the co-ordinates from decimal degrees to UK National Grid, but the resulting points were offset from their true location. I suspect this is because the spreadsheet does not take into account some difference in geoid or datum¹, but I’m not sure.

But, there is another piece of software available from the Ordnance Survey called Grid InQuest that you have to email them to get a copy. This appears to correctly convert the latitude/longitude from GPS to Eastings/Northings. However, in this conversion process the elevation is lost, but this is not of importance to me, and is usually rather inaccurate anyway.

A little bit of manipulation is then required in Excel to combine the eastings and northings into one column and remove duplicate points, before plotting in AutoCAD as a polyline.

Summary of Steps Required

1. Export GPX file from GPS
2. Convert GPX to CSV in GPS Babel, using standard parameters
3. In Grid InQuest, File>Convert File(s)
   1. Select delimited by commas, and Geodetic (Lat, Long) coordinate format
   2. Set Latitude, Longitude and Ellipsoidal Height as columns 1, 2, and 3 respectively (although there is no data for the height in the GPX file, it still works).
   3. Set Projected coordinates (Eastings, Northings) as the output format, and append to existing files (or specify a filename).
4. Open the CSV in Excel, and add the following formulae in the next blank columns =D1&","&E1 where D and E are the columns of eastings and northings respectively, and =IF(F1=F2,"",F2) to filter duplicates.
5. select all the data, press ctrl+L to make a list (the data probably doesn’t contain headings) then, using the drop down arrow on the last column, auto filter then data using the condition “Does not Contain” and leave the box blank. This will give just the individual values.
6. Select just this last column of data, and copy to the clipboard.
7. Finally, to plot these into AutoCAD, type pl to start a polyline and press enter, then paste the concatenated co-ordinates and press enter to finish.

There is doubtless an easier way to do all of this, and I would be interested to know if you have any suggestions. But I thought I’d put this up here in case it prevents someone going though the same headaches as me.

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¹ The Wikipedia page on OS National Grid has a section on the differing data for WGS84 used by GPS and OSGB36 used for the UK National Grid, which might be the source of the error.

I’ve just finished reading Edwin Danson’s book Weighing the World — The Quest to Measure the Earth.

It is a historical tale of how we began to understand the physical shape of the world in which we live, although it does have some technical descriptions of the methods used. It also contains a lot of historical context, which while useful, distracts from the main thrust of the book. There is also a lot of explaining who people are, what rank they are of have just become, and who their friends and enemies are at that current point in time.

It is not exactly the book I thought it would be from the cover, and while it was an interesting read, I would have preferred to read more of the technical aspects and less about the history of relationships between those who undertook the surveys. But then, I am an engineer.

If social history is more your thing, you might find there to be too much technical jargon, so it is a difficult balance for the author to strike.

Overall though, an interesting read, but probably not something I’d go back to

It is possible to use the Ordnance Survey Open Data 1 to 250,000 raster maps as a background layer in JOSM. However, the positional accuracy of this scale of map is limited. This could also apply to the StreetView tiles, but they are readily available as a WMS layer, which is probably preferable.

The OS tiles are in the OSGB co-ordinate system, but OSM uses WGS84. However, there is a plugin that can fix this, and re-project the tiles in the correct location.

Firstly you need to register and download the tiles from the OS, if you do not have access to them. This is free, but can take a while. Once you have saved these to your computer, move the TFW world files from georeferencing files/TFW/ into the main folder with the TIF images.

Then install the Import Image Plugin for JOSM, and restart as required.

To import a tile, select ‘Import image’ from the file menu; browse to and select the required TIF image (with the TFW file in the same folder). This should be imported to the default reference system (which will be wrong, but that is changed later).

Once the image is imported, right click it in the Layers panel, select ‘Layer Properties’ then the ‘Source Reference System’ tab. Type EPSG:27700 in the search field, which should give “OSGB 1936 / British National Grid [ESPG:27700]”. You will probably want to ‘Set as Default’ so that this step doesn’t need to be repeated. But you also need to click ‘Apply Default’ at the top to re-project the image, this isn’t done when setting the default.

This should give the OS 250k raster tiles as a background layer, in the correct location with standard OSM data. Additional tiles have to be imported as separate layers, and need to be toggled when tracing at boundaries, because the images have been rotated and scaled as part of the re-projection.

addenda This should also work for any other image map using UK National Grid, where you have (or can create) the appropriate world file for the extents of the map.

Constantly typing source: OS_OpenData_StreetView when editing OSM was becoming tiresome. Therefore I hacked together a quick sources preset based on one for Spain by user Sanchi. Perhaps this will be useful for others editing OSM in the UK using JOSM.

With one or more nodes or ways selected in JOSM, simply click on “Data Source” to open a dialogue box to quickly add in the source(s) used.

To install, open the JOSM preferences and select “Map Settings” (the 3rd tab down) and then the “Tagging Presets” tab. Click the + to the right of Active Presets, and enter a name such as “Data Source UK” and the URL http://drnoble.co.uk/files/OSM/Presets_Data_Source_UK.xml. This should be available after restarting JOSM.

You may wish to add a shortcut icon to the toolbar, rather than using the menu item each time.

Version History

• 0.3 (2012-01-02) Current version added ‘OS_OpenData_VectorMapDistrict’ and note/fixme fields
• 0.2 (2011-12-28) added ‘local knowledge’ item
• 0.1 (2011-10-15) first version