[Therion] Transparent map-images, oops I mean transparent sketches

Bruce Mutton bruce.mutton at paradise.net.nz
Sun Jun 14 23:21:07 CEST 2009

Oops, I was using the wrong terminology,
What I meant was "transparent sketches", as in the syntax below;

sketches on        # on/off # morphed sketches

Anyway, to continue...

> there is no way to make a jpeg transparent. Use png instead

Yes, on reflection I think I'd worked that out previously, and promptly

> Isn't much simpler to glue pictures in Elements?

I had not considered this. I was heading in the other direction, considering
cutting up the existing scanned maps into smaller portions, (and erasing
passages above or below the passage of interest), so that they could be
handled more flexibly with therion.  A bit like the concept of scraps for
drawings, but using it for the 'sketch' images.

For instance I could produce a map of only the middle levels in one part of
the cave if I hand smaller 'sketch' image' pieces, rather than having to
always see all of the passages above and below.  

Also distortions due to the (very poor) loop closure on the original maps
being different to the therion loop closures means that one large 'sketch'
image' will be handled poorly, but small 'sketch' images' may be an

To explain the background...
We have a 60km (and growing) cave system that has about four plan maps (the
'sketches') that cover the bulk of the cave, each covering 10 - 20km of
passages that intertwine above each other.  The paper maps are clearly a
dead end, and therion offers a way to manage the data and drawings into the

As a semi-permanent stop-gap measure we are trying to enter a skeleton
framework of the survey data into therion, and overlay the 'sketch' images.
Currently we have two 'sketches' loaded, such that with about 25km of survey
data entered we can graphically represent 30-35km of cave.  Five km has been
drawn with therion, the rest as described above.  The current therion pdf
output is about 18 MB in size, obtained with about 1.5MB of 'sketches' as

So, should I be persevering with transparent backgrounds and possibly
smaller 'sketch' images, or stitch them all together and lose some


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