[GIS] Create collection from selected objects

mapbasicmapinfo

I have a table with a series of objects in it. Each record has a reference number but these numbers are NOT unique – e.g. there are two records with reference "01" and each of them has a different object attached.

I would like to combine all objects with the same reference number into a collection object so that I can attach these collection objects to a different table. I should end up with one row per reference number with no duplicates and without losing any of the objects.

I could use "Objects combine" but this will do a geographic union which is not appropriate – some sites are subsections of sites with the same reference number.

The documentation for the "Create collection" statement only shows it being used to create objects.

Best Answer

I thought you might be able to do it using SQL, but it seems Mapinfo doesn't allow you to combine geometries using SQL - Manifold, which I've also used, does.

One way may be to convert the table file into a database (SQLite or PostGIS), possibly using QGIS and then perform an aggregate ST_Collect query grouping by reference number

Related Solutions

[GIS] Copying objects to existing records in MapInfo

How about running an SQL join:

select tab1.attr1, tab1.attr2
from tab2, tab1
where Tab1.Site_ref = Tab2.Site_ref
into q_ToSave

commit table q_ToSave as "C:\NewTable.tab"

This works.

If Tab1 doesn't have objects in it then the order of the tables in the from clause is not important, but if there are objects in tab1 to be replaced, then specifying tab2 first in the list will ensure that the tab2 objects are saved in NewTable

An alternative using undocumented behaviour (including a second object column in a query) is to do the following. This requires that Tab1 is already mappable, and Tab1 must be first in the from clause list:

select tab2.obj "Tab2Obj"
from tab1, tab2
where Tab1.Site_ref = Tab2.Site_ref
into q_ToSave

update q_ToSave set obj = Tab2Obj

This should directly overwrite the objects in Tab1 where the join is true.

[GIS] Easy way to Create Vector Grid polygons

An alternative approach would be to use a database engine (could be MapInfo) to analyse your result data and generate a file that could then be plotted in MapInfo as a vector grid:

Assuming Result data has a format like the following: X, Y, Value...

Decide on the cell size of your MapInfo vector grid
Truncate the X and Y coordinates to the nearest whole number of cell sizes
Summarise (group by) the truncated X and Y columns generating the summary data that you require - mean, count etc.
Transfer the summary into MapInfo and plot points from the truncated coordinates - these should plot in the lower left corner of each grid cell with data.
Convert the points into grid cell squares using the following MapBasic code (could be in a MBX, or from the MapBasic window):

set coordsys table ResultPoints
update ResultPoints set obj = mbr(createline(centroidx(obj), centroidy(obj), centroidx(obj) + GridCellSize, centroidx(obj) + GridCellSize))

(You need to substitute the value from step 1 into the second line in place of GridCellSize)

The result should be very similar to what you were aiming for originally.

Best Answer

Related Solutions

[GIS] Copying objects to existing records in MapInfo

[GIS] Easy way to Create Vector Grid polygons

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