[Xastir-dev] RE: [Gdal-dev] Re: Re: how to extract data from OGR (fwd)

[Curt, WE7U]

This was posted on the gdal-dev list today.  Thought it interesting.

Perhaps we can get to 50fps in Xastir someday, but going to an SQL
database and converting our vector maps to an efficient format when
we import them to the database?  That's fast!

--
Curt, WE7U			         http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
"The world DOES revolve around me:  I picked the coordinate system!"

---------- Forwarded message ----------
Date: Thu, 20 May 2004 00:45:35 +0200
From: L Pool <marisap at telkomsa.net>
Reply-To: gdal-dev at remotesensing.org
To: gdal-dev at remotesensing.org
Subject: RE: [Gdal-dev] Re: Re: how to extract data from OGR

Hi Jacob,

I agree with what Frank says here. If you're worried about rendering speed
then you shouldn't be rendering directly from the Vector File.

I don't even keep them in memory after reading them to a reduced structure
that only contains vertices (or the like) - some of these Vector Maps are
huge!.

I've written a viewer in OpenGL that utilizes the OGR library to capture
Vector Data. I use Display Lists of GL_LINE_STRIPs (GL_POLYGON are a bit
slower) to render each (OGR)Geometry, organized according to their Layers.

Also, I check whether a Geometry intersects with my viewing volume before
calling its Display List - this reduces overhead considerably - its not
necessary to draw things that are out of your field of view. And if a
Layer's Envelope is outside of your Viewing Volume you can avoid iterating
thru its (child) Geometries.

Currently I'm loading 400 MB Vector Files with Raster Maps to boot and my
application never goes below 50 fps on my Radeon 9600 Pro.

Ok. Now for something totally unrelated - this is a question for pretty much
anyone who can help me out with a little bit of knowledge on Geographic
Projections in GDAL.

- --snip--

Louis.