too many points

I got too many points on my autocad drawing of a landscape profile. I
need to output the points in an ascii file, which I have gotten
autolisp to do, but there are way too many. Can I snap the points to
a grid? I need the points output on a 25mm by 25mm grid, size 2
metres by 4 metres. I am getting over 37000 points-too much detail, I
only need around 4000 points. Can I get autolisp to select only the
points closest to my grid, and ignore the other points???

 

If you know LISP, you could use command calls to ERASE or CHANGE, and use
offsets from your grid for the "from point" and "to point" prompts to make
selection windows. Do this is a loop where you feed the next pair of
diagonal points from the grid to the command call. You could put them on a
layer that you freeze, or just trash them.....This would run fairly quickly.

A slower approach would be to single out the data closest to each point in
the grid sequentially, and change them, or change the rest. This would
require a bit more cycling but it doesn't sound like THAT much data.

FWIW, I wouldn't go MOVING the data to your grid points if accuracy means
anything to you. If you have to have points right on a grid, you might
consider interpolating. I've been developing a routine lately to do this and
other things and you are welcome to it. It's on my site, called TOPO.LSP.
It's really raw right now, and I'd appreciate any feedback on it.