skibuf23,
There are essentially two ways to run Turn.lsp.
1) If you are starting your path as a straight line, your vehicle block needs to be parallel with the straight line with the little circle at the center of the left front wheel of the vehicle block sitting on the endpoint.
2) If you are starting your path on a curve, your vehicle block needs to be tangent to the arc with the little circle as the point of tangency and this point needs to be on the starting endpoint of the arc. As already described, if you were to draw a radial line from the center of the arc to the starting endpoint of the arc, the radial line would be perpendicular to the side of the vehicle block.
I realize that you are likely already clear on these two points so let me elaborate a little more. Assuming you are using a vehicle with a truck, hitch and trailer, both of the above scenarios use a vehicle block which is perfectly straight; there is no angle between the truck and trailer. The truck and trailer fall in a perfectly straight line. It sounds like you are interested in modeling a vehicle which is already part of the way into a curve and so want to show your starting position with the truck already rotated at an angle relative to the trailer. The software doesn't allow for this however you can still do it using CarlB's suggestion. Based on your description of what you are trying to accomplish, I think that what you are describing is exactly the same thing CarlB was suggesting. I have used this method myself. So if indeed you want to show a truck with a trailer starting part way through a curve, as opposed to the beginning of the curve, where the truck and trailer are at angle to one another due to being in the process of turning, the method you are describing is what you would need to do. Keep in mind however, that the instances of vehicle plots shown along your path are not blocks, but polylines representing the location of the truck at various points along the path. There is only one block; it is a block with attributes and is the block you place at the starting point of your path. Turn.lsp uses it along with the front left tire path to generate the model.
So what you need to do is start your path beyond and before where you need it to begin, and as you said, delete all vehicle plots that are before your desired starting point and trim the track lines behind your starting point. This is all that needs to be done and is what CarlB was suggesting. To quote CarlB "If you want to simulate an already-rotated vehicle, extend the polyline beyond the start point, a distance/radius as necessary so the vehicle is rotated when it reaches the "start". " That's pretty much it. Nothing complicated. Don't over-think it.
I don't understand what you mean by "rotate this configuration to the geometry of my roadway at my starting point". There is nothing to rotate. You draw your path meandering through your site and generate the model. This is not the same as using templates. Templates are inserted into drawings and rotated to your road geometry to see if vehicles can make it through or not. Templates are old-school and this software has nothing to do with templates. You don't generate a model and insert it and rotate it into your road geometry. This would be assuming that you are simply creating templates with the software and putting them where you need them. That's not what you are doing. You simply draw the path through the entire site, or through whatever part of your site you are checking. What I typically do is copy my site plan drawing to another file with a file name with the word "turn" in it, then I draw my path through the site and generate the model. The end result is a site plan drawing showing a truck driving through it with all of the paths of the wheels, hitch path, and locations of the truck along the path. I've drawn very complex paths through very tight sites with lots of turns this way. However, it is next to impossible to get it right the first time around. You create a path, run the routine and see what you get. It usually takes several attempts to get it right and you have to tweak your path until you get what you want. In tweaking the path, you may have to change the turn radius, although making certain it's greater than or equal to AASHTO's minimum turn radius for the vehicle in question. You may also have to tweak the location of straight portions of the path. You have to play with it. But don't generate a path and rotate it into road geometry. Generate the path within the road geometry and tweak it until right. The end result is that you will be able to see whether the vehicle will fit through your site or not and you'll have a nice exhibit demonstrating that the vehicle can either make it through the site or not.
If you go to the talk page on the WIKI, I've made several posts explaining other aspects of the software and how it functions, including wheel locations, etc. You don't need to read any of those posts. All you really need to Model Imperial Unit AASHTO Vehicles are the blocks and PDF instruction at the WIKI. I created the blocks and PDF instructions, by the way. However, I'm not one of the developers, I just contributed the blocks and PDF instructions. There were a lot of questions on the talk page by users who couldn't figure out how to create vehicle blocks or use the software properly. I have to admit, I found it a little confusing initially, but studied the code and played with the software A LOT in order to make certain that I could generate models that were as accurate as possible using the parameters as defined in the software code. I've used this routine for a few years now and think it's a great free alternative to the expensive software programs available for purchase.
I think I've run my mouth long enough! Anyway, good luck!
Kevin
