Dear all,
I'm using the com.bbn.openmap.dataAccess.shape classes from some Coldfusion
scripts to read the contents of ESRI .shp files and have been largely
successful, so thanks all round for OpenMap!
I can read everything I need to from both points and polygons, but have a bit
of a puzzling issue with the polygon vertex coordinates. My .shp files always
have their coordinates stored as x & y values against the UK national grid.
Reading the coordinates of a point is simple enough, I call the getLat() and
getLon() methods and the numbers are returned exactly as they exist in the .shp
file.
However, when I look at the results of getLonLatArray() from the EsriPolygon
object, the numbers come out scaled down by a factor of approximately 57.29.
The javadoc suggests that all lat & lons are stored internally as radians. The
units themselves are largely irrelevant as I'm not processing them at all using
the OpenMap classes.
In a straw clutching moment, I tried putting the getLonLatArray() through
ProjMath.arrayRadToDeg() in the hope that would undo whatever transformation
was applied when the EsriPolygon objects were created, but that wasn't helpful
either.
I guess my question is:
- what transformation is occuring with the polygon coordinates that isn't with
the point coordinates?
- and what, exactly, is the inverse operation?
I need to know pretty precisely what the scale factor is as I'm surveying data
down to sub-metre accuracy in places, and having things shuffle about due to a
transformation error would be embarrasing.
Thanks in advance,
Dav stott
--
--------------------------------------------------------------
Dav Stott Phone: +44 (0)1904 462137
Systems Development Engineer GTN: 5129 2137
Information Systems Team
Central Science Laboratory Fax: +44 (0)1904 462111
Sand Hutton Email: d.stott_at_csl.gov.uk
York YO41 1LZ, UK WWW: http://www.csl.gov.uk/
--------------------------------------------------------------
--
[To unsubscribe to this list send an email to "majdart_at_bbn.com"
with the following text in the BODY of the message "unsubscribe openmap-users"]
Received on Fri Sep 23 2005 - 09:29:19 EDT