Template talk:GBthumb
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[edit] Usage
Use this template as:
{{GBthumb|e|s|gr}}for example{{GBthumb|120|134|SE370780}}
where:
- e and s are the eastings and southings offset in pixels from the northwest corner of gb4dot.png, the map to the northwest corner of dot4gb.png, the dot. dot4gb.png is 8 x 8 pixels.
- gr is the grid reference in any format acceptable to {{mmukscaled}} - usually a six figure "Landranger" style grid ref (as in the example above) or a four figure reference, eg. SE3778. No blanks allowed in either case.
[edit] Finding e & s
I won't pretend it is easy to find e & s for the dot position. I did look at the possibility of calculating them automatically from the grid ref but unfortunately Image:gb4dot is not drawn on the OSGB36 projection. Here is how I do it.
- Save this version of gb4dot.png scaled to 180 pixels wide on to your machine. Find an image editor that will report the cursor position in pixels as you move over an image - I use Paint Shop Pro but there is plenty of choice. These are once-offs and will do for any number of edits.
- Find the grid ref for the place of interest. I prefer streetmap for this.
- Code the template call with e and s omitted:
{{GBthumb|||SE370780}}. Preview the edit and click on the "map sources" link, being very careful to open in new window. - Select the "Find this location on Multimap - with circle (using lat/long)" link. Zoom out to Multimap's 1,000,000 or 2,000,000 scale - the circle will be preserved.
- Go into your image editor, open the image you saved at the first step above. By comparing that with multimap, find the point corresponding to the place of interest, read off the position and remember to subtract 4 in each direction (because the templates wants the northwest corner of the dot image, not the centre).
- Edit these figures into the GBthumb call and preview again.
For coastal locations it is fairly easy. For inland, I like to take fixes on coastal features, eg. for Catton, North Yorkshire, I noted that it is due west of Filey and due south of Tynemouth. One pixel at this scale represents 4 km on the ground, so the dot is about 30 km wide - precision is not vital. -- RHaworth 16:46:47, 2005-08-09 (UTC)
If you know the location well enough that you can pinpoint it on the map, then the Firefox extension MeasureIt is great for finding the location. Just go to the Template:GBthumb page, fire up MeasureIt, select the centre of the dot and then drag down to your desired location. --Ltn100 10:33, 19 June 2006 (UTC)
[edit] Accuracy?
Are these maps accurate? I've just been going through a lot of Somerset geography stubs, and in most cases the dots are placed well within Dorset. Have a look at Broadway, Somerset, for instance. The dot is well to the southwest of where it should be, and is placed quite close to Dorchester. Grutness...wha? 03:09, 6 August 2005 (UTC)
- Don't blame it on the template. Obviously it is the editor who uses it that you need to contact. In this case, I agree, Steinsky's dot is about 7 pixels too far east. -- RHaworth 07:13:24, 2005-08-06 (UTC)
- Makes sense. Sadly, it looks like a lot of the dots on a lot of the Somerset stubs are in that same place (Kingsdon, Somerset is another one, as are Henstridge, High Ham, Keinton Mandeville and Kingsbury Episcopi - and that's just in H-K. High Ham's the worst - the village is just southwest of Glastonbury!). Perhaps someone just copy-pasted without checking the numbers? Grutness...wha? 11:37, 6 August 2005 (UTC)
I'm having trouble with my browser - the dots come out below the picture. If I put negative numbers in the "top" parameter, they land on the picture. Evidently my netscape browser locates things differently. Has anyone had any experience with this? is there a fix? PAR 11:44, 24 November 2005 (UTC)
[edit] SVG
I've created a vectorized version of the map from VMAP0 and GSHHS. It's not exactly pixel-perfect at 100% of the raster (very close though), but this doesn't matter because the maximum accuracy is only 1/259 for the locator maps anyway. Changed the scale, too; it was a bit silly just to have kilometres on a map of Britain. —Wereon 17:50, 8 August 2006 (UTC)
- There's a small Perl program to calculate dot co-ordinates, too, at User:Wereon/gbthumb.pl. (The page source is nicely formatted, even if the HTML isn't.) — Wereon 12:54, 9 August 2006 (UTC)
