RE: [OpenMap Users] rendering problem still remains

From: Hudson Brian R Contr AFRL/IFSF <>
Date: Tue, 5 Oct 2004 14:43:39 -0000

Don gives some suggestions here on how to modify OpenMap to use doubles.
Many people seem interested in this, but I haven't heard of anyone doing it
successfully. Don indicates that is a large job.
I'm not sure that rendering in XY will help. When you are at that scale
OpenMap attempts to determine the XY location of things based on its
lat/lon. At that scale the lat/lon per pixel is so small that rounding
errors (and precision) can really mess up the drawing (as you can see by
using the drawing tool). You could attempt to use XY rendering but in order
to get the XY points won't you have to use the projection classes to turn
your lat lon points into XY coords? Doing this will cause you to suffer the
rounding/precision problems that OpenMaps lat lon render type is having at
the at scale.
You could possibly write your own lat/lon to xy function that would take the
scale and top left/bottom right lat lon points, then using doubles calculate
the delta per pixel, then using that information to calculate the XY coords
of your rendering in order to get a bit more precision.
Brian Hudson

-----Original Message-----
From: [] On
Behalf Of Rubén Ruiz
Sent: Tuesday, October 05, 2004 9:22 AM
To: Openmap Mailling-list
Subject: [OpenMap Users] rendering problem still remains

Hi all,


Fitst of all i would like to thank to Brian Hudson for his ideas...thanks


When I use XY / XY-Offset Rendering type I can draw perfectly,
problem is not just when I'm drawing, I've a set of maps coming from
autocad, I've managed to translate them into shapefiles in Lat/Lon. The
problem comes with many lines/polygons using a high scale (1:62) projection.
The normal polygons are more or less "visible", but all my circles are not.
I don't know if I can change the rendering type for all my lines/polys when
I load them or anything similar. Also when I draw a nice circle with
XYOffset and I save it in a SHP, it really stores a rectangle, and if I load
that shp again I can see a perfect rectangle...I cannot store nothing
rendered with any XY render type.


At this point I've been thinking in varius exits to this problem:


- if its possible to render XY all my graphics I think it'll be
solved, but I've tried with no success...

- if it would solve this problem...could I change all float members
to double or is there any restriction that makes it impossible? Do you know
where can I begin to change and what portion of openmap do I've to change? I
think the main problem resides in the projection classes but I need some
"light" from you, I've not been working with openmap too much, and every day
I find new fancy things.


I hope someone can help me...


Thanks in advance,


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Received on Tue Oct 05 2004 - 10:48:06 EDT

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