Re: SUM MI-L region centroids to points

[Chichester Harbour Conservancy]

Dear List

I would like to thank all 20 of the people who replied to my question from
all around the world.  The replies mainly consisted of two methodologies. I
used the Mapbasic because it was unbelievably fast  (I am however a
pre-beginner in Mapbasic (!) so this was an excellent starting point).  The
fantastic thing was that it took all the attribute data with it - it is
however very important to use a copy of the file as the polygons completely
disappear.  I have included the two main methods but at the end I have also
included a slightly different idea from Laurence Seef and an xy.mbx routine
suggested by Stephen Baig.

A.  save your polygon file under a new name (say new points)
open newpoints as a mapper
open the mapbasic window  (options>>>open map basic window)
type in the following>

update newpoints set obj = createpoint(centroidx(obj),centroidy(obj))

hilite the text and press return

this will only process on centroid per polygon if you have complex polygons
(ie two polgons that act as one object), you will need to split them up
first.

B.  make a copy of the table of your regions and add two columns to the
attributes called XCOORD and YCOORD (type = integer). Now do a "Table >
Update Column" and update the two columns with CentroidX(obj) and
CentroidY(obj)

Now do "Table > Maintenenace > Table Structure" and uncheck the box that
says "Table is Mappable" this will remove all the map objects from the
table.

Now do "Table > Create Points" and select the copy of you regions table.
Select XCOORD and YCOORD as the two columns to make the points from, hit the
"projection" button and select british national grid and Hit OK and hey
presto you have your points along with the relevant attributes.


C.  You must have a unique key field to do this (explained later). If you do
not
, then create a new filed and update it with "rowid" (leave off the "" when
updating).

1. Save a copy of your table to a new name (lets say JPoints).
2. Open JPoints
3. Table -> maintenance->table structure-> Jpoints. Uncheck the "Table is
mappable" checkbox.
4. Table -> maintenance->table structure-> OrgTable. Check index for key
field.
5. Table->geocode. Select Jpoints and unique key field. In the "search
table" box select OrgTable and Key field
6. OK.


D.  Make the region file
editable and then use the tool add_xy.mbx.  I believe I found this .MBX
through  the Mapinfo_L.  If you aren't able to find it please let me know
and I'll forward a copy to you.  Remember, once the regions are reduced to
the centroid points they may not be recovered.  If you later will need the
regions save a duplicate file!!

Thank you all again

Best wishes

Jacqui Foskett


-----Original Message-----
From: MI Digest <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
<[EMAIL PROTECTED]>
Date: 07 June 2001 10:38
Subject: MI Digest V1 #388






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