exactly my point, not sure why people think they have to take the same number of shoots for a larger contour interval.
exactly my point, not sure why people think they have to take the same number of shoots for a larger contour interval.
let me give an example from a previous work I did with a larger scale map. there was this road running through the property. told the crew that they need to get cross-sections at every 50m intervals since this was what the client wanted. after the data was processed and a planimetric map with contours, profiles & cross-section lines was created, the client had his engineers check on our work. Several segments between the 50m did not correctly represent the actual road. Profile showed road had a sharp slope when in reality it kind of went up, leveled off a bit then went up again. But in the profile the leveled portion was not reflected because it was between the 50m interval. If we get every break/change in profile then we are really doing a 20m (or better) interval cx for a 50m cx pricing.
Explained this to the client that if he wanted a more detailed we need to use 20m intervals. So in order to avoid such scenarios we quote on what we think is needed to get enough data to show the "real" picture.
so if there is a 2 meter pond or depression somewhere in the property, am I so ignore this completely?
I am sure the client would call me up next day & ask "where is my pond?"
A pond is a little different in that it's also a planimetric feature, you would still need to show it horizontally, but a 2m depression yes, you would basically ignore it.
Your main point is exactly right, the client is asking you for something but your professional judgement is that he's asking for something that won't get him what he really needs. This is why I always take a few minutes when a prospective client calls to ask what they are trying to accomplish, and what they expect for their $. Then if I feel they are asking for the wrong thing, explain to them what I think they really need. If what you are suggesting winds up costing less than what they initially ask for, they will always like it. If what you suggest costs more, but you can explain to them why they need it, they'll usually realize that you are saving them money in the long run and will appreciate it in the end.
In this case if what he's after is enough topo to do some serious engineering design, but he's just trying to save a few bucks, a 20m interval won't get him what he needs at all. But if he's just trying to figure out which 100 acres of his property might be the best area to start thinking about for a well or a house with a view, 20m intervals might get him what he needs. Hard to say without knowing what he's after and what part of the world we are talking about.
On the majority of places where I work a 20 m contour would have one such line about the middle of the property. Everything else would be less than 20 m higher or lower.
I have a really old handheld GPS unit. I found topographical software for it, so I installed it and started looking. No countour lines. I thought I had been gyped, but then I "zoomed out" to look at the north half of the state of Mississippi. Yep, I found the contour line. I think there is only one 500-foot contour line for the entire state. Sheeeeeesh.....
David Baalman, post: 381268, member: 11919 wrote: Working on memory here but as I recall the standard says all points sampled are within 1 contour interval, and 90% of the points sampled are within 1/2 the contour interval. So do you really have to shoot every little break line and every little jog in every break line to guarantee that every point on the map is within 10m vertically? Of course not. You can ignore that break where it changes from 7% to 7.5% slope. You can ignore that little 1' ditch alongside the dirt road. You need the MAJOR breaks, and then only at widely spaced intervals. In many cases you could just shoot the 4 corners of the parcel and generate 20m contours to that standard, so in most cases it would certainly lower the cost. The guy is trying to tell you that he just needs a rough topo, maybe for feasibility study or something? Telling him that a rough topo costs the same as a really good topo probably doesn't make him think he's getting what he's paying for.
Problem is he or someone else will almost definitely use the rough topo for something it's not intended
The client obviously wants 20 m contours.
Maybe he thinking contours 20 m apart horizontally?