[Therion] Cave Overlays on Google Maps Web Sites

Bill Chadwick W.CHADWICK at sky.com
Wed Jan 31 21:16:47 CET 2007


For Upper Flood I have been starting from a PDF with UKOS 100m grid ex
Therion, converting it to a two colour White/Transparent and Magenta png and
then using the free MS Mapcruncher (see my bit on the www.mapki.com on how
to load Mapcruncher tiles into Google Maps). For Swildons etc, I simply
scanned pages from Mendip Underground (I have asked Tony Jarratt!).
Mapcruncher does a fair job at anti-aliased resizing. You can edit
Mapcruncher's XML project file by hand to use known survey - WGS84 Lat/Lon
correspondences.

Ideally, for raster layers, the cave would be re-rendered with a decent line
width and text size at different zoom levels, hence my suggestion for
including the raster rendering into Therion. Also when showing a large map
area with a raster cave overlay, some way of merging cave data from multiple
source surveys onto a single Google overlay tile is needed. 

A server based solution would be nifty. Surveyors could simply post their
georefed survey (GeoTif/PDF/KML) and it would appear on a Google Maps or MS
Virtual Earth website. It should not be too much trouble to generate the web
page code automatically.

Google Maps and MS VE use the same simple spherical Mercator projection. 

Google Maps can display a KML file as an overlay (2Mbyte limit I think). I
guess rendering cave overlays from KML might solve some the linewidth
scaling and the survey merging problem of the raster solution. Does anyone
have an online example ?

Landowner / access controller sensitivities must be respected on any public
website. For my Mendips page, I worked with the UK CSCC. We have a 'no
location without access information' rule.

Bill Chadwick

-----Original Message-----
From: Julian Todd [mailto:julian at goatchurch.org.uk] 
Sent: 28 January 2007 18:45
To: therion at speleo.sk
Subject: Re: [Therion] Cave Overlays on Google Maps Web Sites


Martin Sluka wrote:
> On 27.1.2007, at 22:09, Bill Chadwick wrote:
>
>   
>> It is quite easy to create a web page that shows a cave survey
>> overlay on
>> top of Google / Virtual Earth maps.
>>     
>
> Good work!
>
> There is only one problem - google doesn't calculate with underground  
> in 3D - so you may not see the vertical dependencies, the caves are  
> always on surface.
>
> Martin
>   
It looks like simultaneous invention all round.  I'm doing something on 
this too.  I think it should work for any paper survey that you can scan 
and upload, not just computerized ones output from therion or tunnel.  I 
have a server which can do tile cutting of a large bitmap of a cave 
survey.  It's going to be important to create a mask of transparencies 
so you can see it overlayed without all the whitespace outside of the 
cave passage. 

Julian T.








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