Jon,
I've noted the reponse from Northwood about this, and agree that continuing
to manipulate the files in VM is often a good option, rather than taking in
back into MI as a contour file. When datasets get large, working with VM
grids is significantly quicker.
Sometimes you want to work in MI however. The syntax of your SQL doesn't
quite seem right. You're dealing with 2 vector files, there needs to be a
geographic operator that joins them, something like "Where
Spring_contour.obj intersects sld_contour.obj."
As you only want subsets of those two tables, you will need a couple of
steps; select where spring contour is >100 and save it. Select where sld
>40 and save it. Then find the intersection between these two tables using
the geographic operator described above. This will find cases where the two
objects intersect, but not the area where they only overlay each other. To
find the common area of both, better to use one file to cut the other,
using the "object-delete outside" function.
MI SQL doesn't seem to be able to execute a query using a combination of
geographic and attribute conditions (or maybe I just haven't worked it out
yet).
If all that sounds too hard, we're back where we started, just do it in VM,
and contour the results to use in MI.
Regards.
_________________________
Peter Walsh
Senior Environmental Planner
URS Australia Pty Ltd
Phone : (02) 8925 5500 Fax : (02) 8925 5555
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Intersections of contours
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onsmag.com
11/09/00 07:09 PM
Please respond to Jon Rees EG
CEFAS
Listers,
I've created two contour plots using Vertical Mapper (of spring tidal
current and suspended load in the North Sea) and wish to find areas which
have high currents (> 100 cm/s) and high suspended load ( > 40 mg/l). I've
tried to use the SQL query :
Fields {*}
Tables {Spring_contour,sld_contour}
Where {Spring_contour.Upper > 100 and sld_contour.Upper > 40}
Group {}
Order {}
Into {highstress}
(Syntax is correct)
(both tables have lower and upper contours)
However, I get the error :
No join specified between tables spring_contour and sld_contour. Invalid
join condition in WHERE clause.
I've checked that there is a region that overlaps both high velocities and
high concentrations.
Any ideas?
Thanks in advance
Jon Rees
CEFAS, Lowestoft, UK.
Email: [EMAIL PROTECTED]
Web: www.cefas.co.uk
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