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maps - feedback wanted printer friendly view  
 
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AuthorMessage
24 Nov 2020 20:31

from:

Martin Wynne
West Of The Severn, United Kingdom



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I mentioned earlier that it is now possible to load the NLS historic 25"/mile maps as tiled maps. Which is great news -- it means maps of any size can be easily captured at maximum zoom without any restriction caused by your screen size, or need to align multiple captures. It will be in the next program update.

I have since discovered that the highest zoom level available as original tiles is level 18 for the 25" maps. The higher zoom levels available on the NLS web site are actually implemented by upscaling the image in the browser. This means of course that capturing higher levels than 18 doesn't get you any more detail, the same level of detail is simply being zoomed larger.

Most browsers use a resampling image upscaler to provide a smoother result than a simple stretch of each pixel.

Such resampling isn't available in Templot when zooming background shapes on the trackpad, because at the high zoom levels we normally need it would take forever and reduce the screen response to a slow crawl through treacle.

But the result isn't very pretty or comfortable to work over:

1. map tiles as loaded:


It can also be confusing -- see for example how the platform edge has merged with the rail above.

A few updates back I added a function to reduce the contrast of map images when working over them, which makes it a lot easier to see what you are doing -- here on the left:

2. low-contrast converted original:


But it still doesn't match the screenshot captures from smooth browser resampling.

So I have found some old resampling code from Anders Melander which could be used in Templot, as a one-time conversion on the background shapes. It's very slow, several seconds per tile, but only needs to be done once.

The difficulty is that there are 7 different resampling algorithms available, with varying degrees of smoothing and speed, and each one can have an adjustable edge-effect setting. Mostly they are optimised for colour photographs, rather than scans of historic maps, so the default settings are not necessarily the best for our purpose. And then in each case there is the degree of zooming to apply. An utter minefield of different settings which would take me forever to evaluate.

From which I need to select 1 or maybe 2 options to offer in the background shapes. Here are some examples. In each case the original as loaded tile is on the right:

3. "Triangle" interpolation only. This is similar to the browser resampling for zoom level 19:




4. "Triangle" interpolation with low-contrast conversion:



5. "B-Spline" interpolation only:



6. "B-Spline" interpolation with low-contrast conversion:



Answers on a postcard. Which if any of these image effects would you find the most comfortable to work over? In each case the original loaded tile is on the right.

I think my preference is for image 5. above -- notice the improved separation between the platform edge and the rail.

There are of course several other settings you might use at the same time -- Templot can also make a negative image, and there are other colour schemes for the templates.

The use of these NLS maps is getting more popular for track planning, so it would be worthwhile finding the optimum screen display for them. This would be optional of course.

It's a pity the 50" maps aren't available for the whole country, but it's great that we now have almost full coverage for the 25" maps.

cheers,

Martin.

25 Nov 2020 08:14

from:

Phil O
Plymouth, United Kingdom



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Hi Martin,

I'm with you, I think version 5 is the best.

Cheers

Phil.

25 Nov 2020 08:34

from:

Tony W
North Notts., United Kingdom

 

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Hi Martin.

I would second version 5.

Regards
Tony.

25 Nov 2020 10:41

from:

Martin Wynne
West Of The Severn, United Kingdom



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Thanks for the feedback. A majority there for the "Spline" interpolation.

But not so fast. :)

To illustrate the minefield I'm in, if the upscaling is increased it's not so clear-cut.

Going up to 720x720 pixels per tile instead of 512x512, the preference maybe swaps to the less intense "Triangle" interpolation (3. below), and "Spline" (4.) is a bit too fuzzy.

To confuse the issue further I swapped to the "bright night" colour scheme for the template:




Zooming out to the more usual browser size, the differences are not so obvious. But we don't do track design at this level:



We could go higher than 720x720, but memory usage increases dramatically, and screen response speed suffers. Maps can easily have 100 tiles or more.

I can also have a fresh think about the low-contrast functions. Maybe with the more intense interpolations it would actually be better to increase the contrast, for a cleaner background?

It seems clear that it's worth doing something to improve on the original loaded tiles, but deciding exactly what to do is tricky. And that's just for the 25" maps. There are also the 50" maps to consider.

Time for a boiled egg I think. :)

Martin.

25 Nov 2020 12:44

from:

Phil O
Plymouth, United Kingdom



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Martin,

I think it will be a difficult decision. Would it be possible to have a hands on trial version, I don't think just looking at the pictures is a fair test, as we all tend to work differently and screen size may also play a part.

I am looking at your latest post on my tablet and the differences are not great, when I have finished lunch, I will have a look on the laptop.

Phil

25 Nov 2020 13:39

from:

Phil O
Plymouth, United Kingdom



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Martin,

I have checked the pictures on the laptop and the images are more or less the same, perhaps it may be that the map area covered by the Lower image is larger than the one above it.

Phil.

25 Nov 2020 17:00

from:

Martin Wynne
West Of The Severn, United Kingdom



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Thanks Phil.

That's the problem, the different effects are going to vary widely on different screens.

Here's another idea, reducing to 2-tone greys:

 

Top left is original 256 tile reduced to 2-tone.

Bottom left is Triangle interpolation from 256 to 768.

Bottom right is Triangle interpolation from 256 to 768, followed by reduction to 2-tone. I think that might work quite well as a design guide.

The template is in bright-night colours.

In the end I'm probably going to have to do a full dialog with all these optional adjustments. But I was hoping to find a default setting which would give good results for most users in most cases.

cheers,

Martin.

25 Nov 2020 17:29

from:

Martin Wynne
West Of The Severn, United Kingdom



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This is what that looks like in full:



And working over it (bright-night colours):



cheers,

Martin.

25 Nov 2020 18:20

from:

Phil O
Plymouth, United Kingdom



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That looks ok to me. Thanks.

Phil.

26 Nov 2020 00:32

from:

Rob Manchester
Manchester, United Kingdom



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Hi Martin,

"Triangle interpolation from 256 to 768, followed by reduction to 2-tone" looks way better for my eyes. But then again nobody else has my eyes :) or my muddled brain :(

Rob


27 Nov 2020 14:58

from:

Martin Wynne
West Of The Severn, United Kingdom



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Rob Manchester wrote: But then again nobody else has my eyes :) or my muddled brain :(

Nor mine. :)

I think I have given up on finding a single setting which gives the best results in all circumstances, there is too much variation in the original map sheets.

So I have created a full dialog, with defaults which should work reasonably well in most cases, but maybe not always:

 

The 2-toning can be set to any desired colours, not only greys, or can be set to match the trackpad colours for the different colour schemes. There is a slider to set the threshold level.

Now to finish writing the code, especially the idiot-proofing for when I click the wrong thing. :?

cheers,

Martin.

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