We are currently working on a project that will require a boundary and topographic survey of approximately 500 acres plus 1/2 mile of road right of way.
We would usually have the project flown for aerial photography and generate contours through this method, but I was wondering if lidar would be a better way to go.
Would anyone familiar with these methods be able to fill me in on the approximate cost difference of lidar v aerial photography?
I believe lidar would be a better option, since we would have actual bare earth points we could import into Civil 3D to generate a 3D surface model, but don't have any experience working with a private contractor in obtaining this information.
The best option would be to have a current ortho photo with lidar points overlaid onto the imagery. Can this be done all in one flight?
Thanks in advance for any advise.
I believe the orthophoto wants to be at a higher elevation. Most likely the orthophoto is already available. So may be the LIDAR.
I have done multiple projects with lidar and orthophotos but was never involved with the planning.
LIDAR is dependent on the software, One project the LIDAR contours were provided by an aerial company via the client. Very jagged and I did Not like them. My software was unable to smooth them. I was also provided the LIDAR points and could do no better. Other than that project I found every LIDAR contour to be within 1/2 contour of my ground shots.
Check if the aerial firms have dual equiped planes. And ask for a sample of their LIDAR work.
Paul in PA
> We are currently working on a project that will require a boundary and topographic survey of approximately 500 acres plus 1/2 mile of road right of way.
>
> We would usually have the project flown for aerial photography and generate contours through this method, but I was wondering if lidar would be a better way to go.
>
> Would anyone familiar with these methods be able to fill me in on the approximate cost difference of lidar v aerial photography?
>
> I believe lidar would be a better option, since we would have actual bare earth points we could import into Civil 3D to generate a 3D surface model, but don't have any experience working with a private contractor in obtaining this information.
>
> The best option would be to have a current ortho photo with lidar points overlaid onto the imagery. Can this be done all in one flight?
>
> Thanks in advance for any advise.
Paul has some good suggestions
I am a big fan of aerial topo.
I am not familiar with Lidar, but am open to that idea... perhaps a combo is cost effective, maybe not.
There is no reason why conventional areial can not provide you with points to create a TIN or the actual terrain model they use to create the contours (in your format)... no need for you to recreate it on your own, and it would be much more accurate.
I suggest you prepare a list of items you need and related accuracies, with a diagram of the project site and location. fax or email to several providers, and then later discuss their fees and methods.
I always prefer to shop local, but sometimes a remote firm can shop out the actual photography with someone local and be very responsive. The firm/firms you are familiar with would be a great place to start.
In the San Diego area I used several providers, and most of them used the same two firms that actually owned an airplane and camera.
Ortho and contouring is automated, and then edited by a human
If you typically fly aerial photography and generate contours from that, why do you want to switch?
Do you want denser points?
If so, you can generate “Photogrammetrically Extracted LiDAR Equivalent Data” which would be as dense, or denser than LiDAR.
Do you want more accuracy?
If so, you could fly lower and get similar accuracies to Aerial LiDAR.
There are definitely planes that have both LiDAR and Image sensors mounted in the same plane to collect simultaneously.
However, LiDAR is much more expensive than just imagery (and data extracted from the imagery). LiDAR plus Imagery is even more expensive than that.
The reason Paul saw “Very jagged” contours with the LiDAR data was because of the point density. Surveyors are used to seeing contours generated from coarse breaklines and points. Once you get a point every square meter or square foot, you get some pretty interesting looking (jagged) contours.
Bare earth points can be generated from LiDAR or Aerial Imagery.
If you are worried about trees, then you fly lower when the leaves are off the trees to see the ground.
LiDAR doesn’t see through trees or leaves as some might think. The only difference between LiDAR and Aerial Photography (Stereo) is that LiDAR only needs one hole to see through leaves where the other method needs two. But, then LiDAR can’t tell the difference if it’s on the ground or on something else. With Aerial Photography (Stereo), you can see if you are either on the actual ground or another object.
We do this type of work all the time and are located in IA. If you are interested in chatting, email me directly.
Aerial Photography v Lidar, LIDAR Is Cheaper
In quotes that I have seen, it is significant.
Paul in PA
> We would usually have the project flown for aerial photography and generate contours through this method, but I was wondering if lidar would be a better way to go.
This is really a question for your friendly neighborhood photogrammetrist. Almost any precision you desire can be achieved with either method, it's a question of cost efficiency.
> I believe lidar would be a better option, since we would have actual bare earth points we could import into Civil 3D to generate a 3D surface model...
Actually, you will have points on whatever solid thing turns out to be the last return. Like branches, fallen logs, etc.
Everyone seems to be interested in how jagged lidar data is. For a while I worked processing and classifying Lidar data. Yes, it might hit a branch, building, etc., but in the classifying stage that can be taken out (or left in) by someone experienced in classifying that data. The amount of return can also be beefed up to get it more accurate...if you want 3 million points in an acre you can do it.
Some thoughts..
You mention orthophoto, but do you need an image? An ortho is a digitally rectified photographic plan view of the project. Great for planning and presentations but strictly a 2D product. A contour map or TIN can be derived form either aerials or Lidar. You don't mention the contour interval but usually two flights will be required to get ortho and contours. Or at least if done with aerials they will likely fly higher to get the ortho.. which in effect flattens out the images and requires combining fewer images to get the final result. Not many companies have the capability to get Lidar and imagery in one mobilization. Requires large aircraft with two ports and much onboard infrastructure.
How close a mapper is to your project matters! Ferry time on these aircraft sometimes costs as much as the photography/Lidar. Sometimes, a competent local outfit using less than state of the art can give great service... don't be overly persuaded by bells and whistles you may not need.
Anyway...lots of things to consider.... someone already gave good advice... talk to a reputable mapper and get educated.
OrthoPhoto Overlain With LIDAR Contours When Available
...can do more than help plan a project.
Sometimes they can be the project.
I have done it.
Paul in PA
Of course, Paul,
You are right again. Sometimes they can be the project. I was just pointing out that sometimes they are not needed and usually require spending more money to acquire. And they are great for planning and presentations.... not to exclude their use for other purposes. Pipeline companies can extract house counts from them, assessors use them together with change detection software to help with tracking land use changes... and on and on. Once again Paul you are correct!
Our mapping division currently owns and operates two Lidar units with cameras, and can produce surface data from either Lidar or photos. In the last few years essentially all of our clients have started requesting Lidar data. Pretty much the only mapping that they do from airphotos now is either historical imagery for comparison purposes or as a quality control check on the Lidar.
As a rule, if the plane is flying Lidar then the camera is running also. There is a separate cost for the images but they provide context to the model that the Lidar doesn't. Without the photo it's almost impossible to see the edges of a creek for example.
Having done my fair share of flight planning in the past, I find it difficult to imagine a project where the flight heights and flight paths and side lap requirements would permit one pass data acquisition for both Lidar and mapping grade imagery. But I've been out of it for a couple years. Or maybe you mean you are just collecting pictures to help with the Lidar processing?
It's not my field, but the experts in the mapping division tell me that the digital photos used to build the orthorectified imagery and the raw Lidar are often collected as part of a single flight.
Okay then that makes sense. They probably use the same breaklines used to produce the orthos to help with the LIDAR contours. At the pace of change in digital mapping, my knowledge base is quickly becoming irrelevant. I'm out two years and things have changed a bunch. Pretty soon I will have to preface all posts with "ya know.. here's how we did it back in the day" have a good one.
My preferred mapping consultant generally flys fixed wing color photogrammetry and low level (150') helicopter lidar for my projects. But I'm looking for a lot of detail in an urban canyon situation and often have to mix aerial and mobile lidar to get the mapping products I need due to Secret Service flight restrictions over large sections of downtown DC.
A Single Flight Does Not Mean A Single Flight Line
Aerial topography often employs multipl flight lines for overlap.
It is ossible to follow the same fohjt line at different altitudes.
Somebody check with the experts.
Paul in PA
Back in the day when I planned aerial flight lines
Overlap was front to back along the flight line to get stereo coverage, often it is 60%. Sidelap is the area along adjacent flights appearing in both sets of images. This is to insure proper neat model coverage. Anyway that's how I remember it.
My Bad, Sidelap
You lose the right words when the work is not fresh in your mind.
I covered aerial planning in college and on the exam, but never for a job.
Paul in PA