reduce number of segmetns in polyline
Accepted solution
You can try PLDIET.lsp, with its PLD command, available >>here<<.
There's also PolylineEveryOther.lsp, with its PLEO command, >>here<<, which is less flexible but much simpler and probably fine for something as regular as your sample drawing.
In either case, you should probably remove [or break-at-one-point at both ends of] the segments closing the ends, or you might get undesirable results there. Then, since you're starting with line segments and reducing the number of them, they'll get kinkier, so use PEDIT and its Fit or Spline option to make them curvy.
Kent Cooper, AIA 
You could try to use a helix object to represent the spiral rather than a polyline with a lot of segments. It does not exactly line up with your spiral but may be close enough. The number of turn is about 9.25. YOu can tweak this value in the properties box for the helix. I estimated the center location for the helix. The green lines are the helix and purple your original shape.
Another approach is to create a spline with fit points at 0°, 45°, 90°, 135°,.. and specify the end tangents. This yields a pretty good match. To adjust the tangency after you created a spline change to the CV mode for the spline and move the next to the end CV as needed. This image shows the fit point I used.
@leeminardi wrote:
.... Another approach is to create a spline with fit points at 0°, 45°, 90°, 135°,.. and specify the end tangents. ....
Or, if it's an option to draw the spiral in a different way, rather than working with something already drawn [such as supplied by someone else or translated out of some other software], you can try SPIRALS.lsp, available >here<. [It's encased in a .zip file -- at the time, we couldn't attach .lsp files directly.] See the comments at the top of the file and under each of the three command names. You would want the SPEQ command in it, for SPiral with EQual spacing between turns [an Archimedean spiral]. It makes a Polyline of arc segments, so it doesn't have the kinkiness aspect of simply reducing the vertices in your original.
Kent Cooper, AIA
@Kent1Cooper wrote:
You can try PLDIET.lsp, with its PLD command....
... updated >here<.
Kent Cooper, AIA