Version 2.0 contour maps .. discuss
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Version 2.0 contour maps .. discuss

 
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GSV3MiaC
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Joined: 14 Nov 2005
Posts: 12

PostPosted: Thu Mar 09, 2006 7:30 pm    Post subject: Version 2.0 contour maps .. discuss Reply with quote

Here are some samples (.jpgs) of a proposed 2.0 release of contour mapping. I've
uploaded them to my website. The area we're looking at is a bit of Skye which I had
a debate about 4 or 5 months ago .. version 1.1 was seriously broken in this area
(for reasons I never did discover).

http://www.quik.clara.co.uk/maps/skyemap1.jpg

should be the current version (1.2) of contour mapping (with voids and suchlike
overlayed). It's a low res .jpg, because that's what I had saved, so don't get hung up
on the picture quality, it's the content that matters.

http://www.quik.clara.co.uk/maps/skyemap2.jpg

Is what the area would look like if I redid the contours as proposed .. biquintic
interpolation (36 point spline) to a 30m square (-ish) grid. Using new V2 NASA
Data (with 75% less voids, although the Northern Isles are still cr&p). Note this is a
progressive .jpg, wait for it to finish refining. The point of note is that the contours no
longer have pointy corners (and there may even be some added at the top of hills,
since the biquintic takes account of slopes and changes in slopes, which
Dem2Topo cheerfully ignores).

http://www.quik.clara.co.uk/maps/skyemap2a.jpg

is zoomed out a bit, so you can see that you now get coastline (accurate to about
one SRTM tile - i.e. 90*60m) and major lakes/rivers. This is derived from the NASA
'water body dataset' shapefiles. All nicely zeroed elevation-wise (although yeah,
some contours can still cut through the 90*60m tile). I have made a stab at labelling
the blue stuff as either ocean/sea, lake, or river, but I wouldn't expect to get close to
right (especially around the Celtic bits of GB).

finally

http://www.quik.clara.co.uk/maps/skyemap3.jpg

shows you what you can have for 135 if you buy the Garmin UK Topo V2 data -
basically 1:25k OS contours and rivers etc. 5m contour interval and much, much
more detailed contours. Copyright Garmin/OSGB/Etc. and provided only for
comparison, as a sales aid for Garmin, and I'll take it down as soon as someone
bitches at me, so if you're reading this posting from somewhere in the 22nd century,
it's doubtless gone (along with all the other links). You can of course view it at
Garmin's website, Lat 57.2N, 6.2W, roughly ..

The downside of V2 is that the map tiles are going to come out 2x to 3x larger than
version 1.2. I was also planning to add 'voids' definitions, and peaks/trig points, to
each of the separate tiles, rather than having one overlay for the whole country (well,
two .. separate one for Ireland). Since I have to combine the water data with each
contour tile, adding the other stuff in isn't much harder.

The Town/island names I'll still keep separate, and the coastline will no longer be
needed, since each tile comes with it's own (and the overview will show the sum of
the whole set .. hopefully).

Oh yes, the Garmin UK Topo mapping is about 10x-20x larger than even proposed
v2.0 of the free stuff would be .. it comes in 1/4 degree square tiles and each one is
around 3MB!!

If anyone is actually interested in a V2, it will take a few days to organise, since
there is quite a few GB of data to crunch and the process got more complicated.

Or we could just stick the revised SRTM data through the same process used for
version 1.x, and ignore the extra resolution, water body data, etc ... comments
invited ..


Last edited by GSV3MiaC on Fri Mar 10, 2006 6:54 pm; edited 1 time in total
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Wildlifewriter
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Joined: 04 Aug 2005
Posts: 948
Location: Norn Iron

PostPosted: Thu Mar 09, 2006 11:32 pm    Post subject: Reply with quote

The refined V2.0 contours look a lot better. Overall, I think this is worth working up. (Easy for me to say, as I don't have to do the work. Smile )

Regarding the "Voids" overlay: Could I suggest leaving it as one file? The reason is, that having one file makes it easy to leave out the voids, when making up a map for transfer to the GPS. Voids only cause screen clutter (especially on B&W displays) although it's right that they should be part of the overall set.

Regarding "Coasts": How much space is added by having the sea as polygons, rather than a simple line?


Quote:
I have made a stab at labelling the blue stuff as either ocean/sea, lake, or river, but I wouldn't expect to get close to right (especially around the Celtic bits of GB).


Perhaps those readers of this forum who currently use SMC Contours could help, by beta-checking the "water" labels. It wouldn't take very long. (I hope.)

Quote:
Or we could just stick the revised SRTM data through the same process used for version 1.x, and ignore the extra resolution, water body data, etc ... comments invited ..


I'd like to help, if any of the work can be farmed out...

-Wlw
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GSV3MiaC
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Joined: 14 Nov 2005
Posts: 12

PostPosted: Fri Mar 10, 2006 12:40 am    Post subject: Reply with quote

It isn't an awful lot of work, but it's an awful volume of data to process (each SRTM tile has 6x as many points, and each point is float32).

Not sure how much the sea as polygons adds .. I'll know when I've done some more tests. Not just the sea - you have wide rivers and lakes too (basically most of the things which should have had constant elevation, or constant slope or whatever). I doubt anyone will get too hung up if XYZ estuary comes out as 'sea/ocean' rather than 'river' .. it still looks blue!

Thanks for the offer of help, but I think only the testing can be farmed out. As I've moaned before, no broadband here, so moving data around in volume is a non-starter, and this has a lot of data. The interpolate times are only minutes per tile, (to get to a .bin/.hdr pair) and generating the .tifs (using 3dem) is just button pushing (and hopefully typing the right filenames).

After that it's import the .tifs into Dem2topo, overnight run to process them all, and then (hopefully) a small program to build/combine the final .mp files, put in believable headers, and then manual work again to compile them.

Actually there is something you/we/someone could do .. would be nice to have some better names for the tiles than W52N003, in my opinion, so if anyone wants to suggest names (the tile set probably won't change much from the current version) feel free. Some are obvious ('Scilly Isles', 'Channel islands') but that still leaves plenty!
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