Strange contours

Are you referring to Mount Parking Stripe, or the contour running through a building, or both?

I absolutely, positively detest contours that in no way resemble true contours. Computer generated contours seem to hold to the theory that sharp corners exist where none could possibly be. I try to picture flood waters moving up or down across the landscape.

Your example is clearly some type of mistake. Whoever the idiot was who did not check his work product adequately should be drug out into the street and shot on sight/site. Garbage like this leads the client and any other viewer to assume that everything else depicted could possibly be wrong.

Many of my clients are savvy enough to understand that jagged, so-called contours do not represent reality. Neither do contour lines that jump across obvious elevation changes. An example of that is a ramp leading into a basement garge door. Providing contour lines that ignore this obvious contour-changing situation show a lack of concern for doing accurate work. Sharp changes will occur where obstructions are met, not out in the middle of a nicely graded area.

Looks like a rod height bust to me. Did another surveyor actually send this to a client?

Just another example of LIDAR proofing gone AFU. For example, look at the 2608 contour running through the building in upper left corner, there has to be at least a 15 or 20 foot elevation change!
Just an example of what you get when you process the data through the lowest bidder … usually in some third world country.
I’ve got a better example than this in my files … 6 feet of elevation change across the water surface of a pond!

No, it is a freebie from our county GIS site.

that says it right there...County GIS. where did the County get the elevations? what was frequency of hard ground shot? what was the error? There are contours on quad maps here in Florida, however most of those were created in the 50' and 60's and old the major improvements (airports and interstates) were added in the 80's. Who is to say what is right without a true topo of the site?

Would that pond be on Moses' property?

Unfortunately not, it is just up the road from me on the HOA detention pond for some million dollar homes.

"Whoever the idiot was who did not check his work product adequately should be drug out into the street and shot on sight/site."

Jeeze Your Cowness,

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I would have guessed that the rodman raised the height of the prism pole to see over a tall van, and the I-man forgot to key it in ... but since it's GIS based, it could be LIDAR bouncing off the top of a car.

PRE-DEVELOPMENT CONTOURS?

county GIS was probably done prior to the construction and no doubt has a disclaimer that you can't use it for anything real.

Looks like at least a couple of problems there. First of all you don't show contours through buildings, you trim them at the building edge. Even without that being done, the 2608 contour in the upper left doesn't look right.

Then the obvious bust; as it is from a county GIS, I doubt it was run conventionally. Also, one shot with a tall rod usually (repeat usually) doesn't produce that shape, it usually makes just one high shot then the busted contours form a kind of pyramid shape. So, it is likely from aerial photos or LiDAR. Yes it could be from a car top, but really, the rest of the contour doesn't seem to conform to what you usually see on a parking lot. It doesn't appear to account for any drainage.

Just looks like a kind of problem area that needs to be revisited.

Stephen

Free LIDAR, You Get What You Pay For

I just completed a proposed pool grading plan in a new subdivision. I field shot my lot, GPSed to get on SPC and vertical datum, brought in an ortho rectified photo and a DXF of LIDAR contours. Every house had a crazy lump. However in between the houses the ground contours were weaving around my CAD contours. No where was anything off by more than half a contour. There is a detention pond at the end of my block and that looks very good also. My GPS points were in clear areas and elevation comparisons were less than 0.5'.

Very good I would say.

Lidar cannot discern between ground and a parked truck, plus you have to understand there is also considerable side scanning. The orthophoto shows you it is a parking lot and you must assume that vehicles actually park there. Get over it and come up with a real problem.

Paul in PA

Free LIDAR, You Get What You Pay For

did it give you hills at the trees too? i recently downloaded some lidar for an area and found the trees and buildings to be included in the model. the ground and water was pretty close to reality.

my cousin works for PaGS. last time i saw here she said the lidar was great and the surveyors loved the information. i was envious until now and cannot wait until I see her again. 🙂

LIDAR Can See through The Trees

I believe better than traditional aerial photo contouring in tree areas.

Paul in PA