Topographical map in a heavily forested area


#21

As StevenB said, you won’t be able to produce any accurate contours for the terrain because all the camera is only going to see the tree canopy - not the ground level.
Since you can’t map the terrain, using PPK in an attempt for accuracy would be a waste of effort.

Just mapping forest canopy without making contiurs, you willl have issues with the problem stitching software will have matching points.
The way to make this (somewhat) better is to fly higher and use bigger overlap like 85%.


#22

While I agree in normal user experiences, I can make a pretty good bet that through external software and point cloud editing that we can come up with a DTM that will be plenty good for conceptual design. Can’t find out if you don’t try. Kind of like leaving a putt a foot short…


#23

Sounds like you’re the expert.
Good luck

From experience, I’d think just trying to get something that could be stitched would be a big enough problem.


#24

That doesn’t matter if there are points in between the canopies.


#25

Actual subject property of this thread with example of potential ground points classified.


#26

Here’s the actual client map from the OP.


#27

Hello, You will never get 6" vertical accuracy on the ground for this heavily forested site even with extensive point cloud editing. The good news for your client is that there is a 2010 LiDAR dataset that will penetrate the treecanopy and “see” the ground with a stated accuracy of 10cm. You can download that data set at The National Map Downloads: https://viewer.nationalmap.gov/basic/

This data set can also be used in Pix4D and perhaps other photogrammetry software to provide ground control without GCPs.

The orthoimage that you wou;ld produce will be very helpful to give a current aerial view of your project site.

The LiDAR dataset will provide accurate an accurate DTM and contours for preliminary thru final engineering design of roads, grading, and drainage. Definately talk this over with the project engineer in charge of site layout and design.

Cheers!
Andrew Price

DATA SET NAME 2010 ARRA Central Coast CA Lidar
DATA ACCESS NOAA Digital Coast - Z3 OR NOAA Digital Coast - Z4 OR The National Map - Z4 OR The National Map - Z3
METADATA ACCESS InPort Metadata - Z3 OR InPort Metadata - Z4 OR Tile specific metadata available in USGS TNM Viewer
COLLECTION DATE Aug 17 - Sep 19, 2010; re-flights Jan 2011
QUALITY LEVEL 3
MEETS 3DEP No
REASON DATA DOES/DOES NOT MEET 3DEP Missing USGS Base Spec products
PROJECT STATUS Complete
RESTRICTIONS Public
DATA TYPE Lidar-Topo
VERTICAL ACCURACY 9.3 cm RMSE
HORIZONTAL ACCURACY Not Provided
POINT SPACING 2 m
VERTICAL DATUM NAVD88
HORIZONTAL DATUM NAD83
PRODUCTS AVAILABLE Custom points, grids, and contours from the NOAA Digital Coast; Points from the National Map
NOTES Lidar Report Zone 3 RMSEz = 6.2 cm, Zone 4 RMSEz = 9.3 cm. Project names in The National Map: ARRA-CA_CENTRALCOAST-Z3_2010 and ARRA-CA_CENTRALCOAST-Z4_2010

#28

Yep, I agree.

“The dataset is from several sources from shuttle radar all the way down to Airborne LIDAR (3mA/1mR) if the area supports it.”

I think that it is great that everyone is sharing their skepticism. I hope to prove you all wrong. If I can’t, then I tried.