Hello Dan,
the proportion area within any another area can be done through Grid Analyser's "Area statistics generator" module. Unfortunately, Grid Analyser works with MI raster format (grid) therefore before applying this function MI vector tables (polygons) must be converted into grids (GA's "region to raster" module).
Regards Stefan
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On Fri, 13 Aug 2004 09:46:32 +1000, Dan Bowles <[EMAIL PROTECTED]> wrote:
Hi list
I don't think some of the responses to my request went to the list, and I
felt some were excellent, thanks guys. I'm posting them now for the benefit
of others who are still in the learning process...
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Hi Dan,
You do have options doing this with SQL:
MB help:
AreaOverlap( ) funtion:
Purpose
Returns the area resulting from the overlap of two closed objects.
Syntax:
AreaOverlap ( object1, object2 )
object1 and object2 are closed objects.
Return Value
A Float value representing the area (in MapBasic's current area units - use
Set Area Units... to change this) of the overlap of the two objects.
Example:
Select AreaOverlap(PolygonTable1.Obj, PolygonTable2.Obj) , PolygonTable1.ID,
PolygonTable2.ID
Received: From PolygonTable1, PolygonTable2
Where PolygonTable1.Obj Intersects PolygonTable2.Obj
Into a Noselect
Browse * From a
ProportionOverlap( ) function:
Purpose
Returns a number that indicates what percentage of one object is covered by
another object.
Syntax
ProportionOverlap(object1,object2)
object1 is the bottom object (not text or points)
object2 is the top object (not text or points)
Return Value
A Float value equal to Area(Overlap(object1,object2) ) / Area(object1).
HTH
SÃren Breddam
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Hi,
I'd recommend you do this as follows:
i) make a copy of the veg layer
ii) split the veg layer into separate polygons for each corridor, NP or SF
do this as follows:
make veg layer editable
select all veg polygons
Objects > Set Target
select all corridors
Objects > Split
save table, then Table > Maintenance > Pack
repeat procedure for NP and SF
iii) use SQL similar to this:
For summary areas by class for all veg layer:
Select class, sum(area(obj, "hectare")) "Area_ha" from veg group by class
order by class into selArea1 NoSelect
For veg areas within NP etc
Select sum(area(obj, "hectare")) from veg where obj within (select obj from
NP) into selArea2 NoSelect
For the percentages of each veg class
Select sum(area(obj, "hectare")) from veg where obj within (select obj from
NP) group by class order by class into selArea3 NoSelect
then you'll need to divide areas from selArea3 by areas in selArea1 to get %
(use "sq km", or "sq m" instead of "hectare" as required)
Fiddly, but very powerful. There's plenty of scope for modifying and
extending the SQL above to do exactly what you need.
Hope this helps.
Best Regards,
Martin Higham
Avantra Geosystems
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Cheers
Dan Bowles
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