Line string validation and ORA-13349 on polygons

Question

Hi all,
We are having the following problem:
Our application accepts linestrings and connects them to create polygons. Each individual line validates TRUE but some polygons validate with ORA-13349. The problem is caused by lines that we call Lightning bolts. These are lines that cut back very sharp on themselves so that one or more points are within tolerance distance of a line segment.
An example:
mdsys.sdo_geometry(2002
,null
,null
,mdsys.sdo_elem_info_array(1, 2, 1)
,MDSYS.SDO_ORDINATE_ARRAY(258699.59,472878.73
,258688.58,472879.66
,258688.589,472879.659));
Oracle spatial seems to be very tolerant in validating these lines but once they are used in a polygon they are not accepted.
Why is this ?
Also we are looking for is a way to detect these lines before the polygons are created.
thanks, Rene

Answer 1

Hi,
To detect the "lightning bolts" this procedure seems promising.
Do a self intersect of the geometry.
Determine de spatial relationship between the original and the self intersect.
If the spatial relationship is not "EQUAL" you have you lightning.
Here is a real life example:
declare
l_geo1 mdsys.sdo_geometry := mdsys.sdo_geometry(2002
,90112
,null
,mdsys.sdo_elem_info_array(1, 2, 1)
,mdsys.sdo_ordinate_array(258727.255
,472853.276
,258724.984
,472848.338
,258714.12
,472852.98
,258709.61
,472854.55
,258710.89
,472859.11
,258712.41
,472865.36
,258712.3
,472868.37
,258711.51
,472871.47
,258709.83
,472874.33
,258704.77
,472877.1
,258699.59
,472878.73
,258688.58
,472879.66
,258688.589
,472879.659));
l_geo2 mdsys.sdo_geometry;
l_result varchar2(100);
l_tolerance number := 0.0005;
begin
l_geo2 := mdsys.sdo_geom.sdo_intersection(l_geo1, l_geo1, l_tolerance);
l_result := sdo_geom.relate(l_geo1, 'mask=determine', l_geo2, l_tolerance);
dbms_output.put_line(l_result);
end;
This example returns an unknown mask 100110001 which I believe should be a OVERLAPBDYDISJOINT. But it is definitely not an EQUAL.
I will have to go and find some more examples to test this method.
thanks Rene