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A single message from topic:  Direct loading of background maps   in forum:  Templot talk
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Single message by Martin Wynne       Topic: Direct loading of background maps
Posted: 10 Sep 2017 03:04
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Martin Wynne
West Of The Severn, United Kingdom

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Martin Wynne wrote: richard_t wrote: Is it possible to load this map (and around it) into Templot using the new functions?

Hi Richard,

That's an individual scanned sheet, not a "slippy map" -- what NLS call their "Georeferenced Maps".

Templot can do only those at present, not the individual sheets. The URL needs to look like this:

and it must change as you scroll across the map.

The individual sheets use a different format derived from Google. I'm hoping to add them in due course, when I have figured out how to decode that URL from the Google docs. I suspect they will want paying for an API subs.
Hi Richard,

Forget all that rubbish. :)

I have now decoded the NLS single sheet URL:

The 25" (actually 25.344"/mile, 1:2500) map sheets are 1.5 miles wide and 1 mile high (inside the margins), and NLS say they are scanned at 400dpi.

Each 6" map sheet was divided into 16 sections for the 25" sheet areas.

128378924 is the sheet number.

lat=7479&lon=6650 are in pixels @ 400dpi. From the bottom left corner of the scanning platen, not the sheet margin or the sheet edge. Why NLS are calling them lat and lon instead of Y and X is yet another of life's many mysteries.

The zoom levels are based on zoom zero creating a single 256-pixel tile from the scanned platen area.

What all this means is that I think I now have sufficient information to scale these individual sheet screenshots.

This would be useful because

NLS are well ahead with the scanning of these sheets beyond the areas so far georeferenced for the slippy map, and

In most cases there are 2 or 3 different map dates available for each sheet, whereas the slippy map offers only one date.

So I will try to get 215b out as soon as possible with the option to make screenshots from these individual sheets, in addition to the slippy maps.



A single message from topic:  Direct loading of background maps   in forum:  Templot talk
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