"Stewart, Andrew R.J." wrote:
> HI, I was hoping someone may be able to help me with this one. I want to contour
>some depth data within a harbour using vertical mapper. However, I need to prevent
>interpolation of the data across a peninsula. Whenever I try to produce the contour,
>the contour lines are connected by adjacent points across the peninsula. Is there
>some way I can prevent this, perhaps using breaklines?
Good question. The best solution is to have depth points spaced
so closely together that the search radius can be set smaller
than the width of the peninsula. Another technique is to have
breaklines beyond which radius searches at cells do not go, but
VM can't do this yet. A reasonable possibility that VM can do
might be to place some zero points along the shore of your
peninsula and use a TIN algorithm. That way triangles formed
across the land will start and end on the shores and defining a
surface of zero depth while limiting data influences across the
peninsula. Of course, you'll also have to be careful not to
overwhelm your data set with too many zero values so as to not
bias near-shore depths too much toward the shallow. Also,
controlling where the zero line falls is an interesting
contouring topic in itself, nor is it a trivial one.
BTW, people who have early versions of VM (especially versions
older than 2.0!) who are thinking of upgrading to 3.0 might want
to do that *this* month. The price is going up $200 by the end of
the month. I've got some info on this at
http://www.ctmap.com/gisnet/catalog/index.html. Upgrade price
from any version to 2.6 is $395, and you get 3.0 free when it
releases. After June 29th, you will not be able to upgrade
versions older than 2.0, and the new prices climbs from US$995 to
US$1195.
- Bill Thoen
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GISnet, 1401 Walnut St., Suite C, Boulder, CO 80302
tel: 303-786-9961, fax: 303-443-4856
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