Terra 4.X: Importing, Matching and Evaluating GCPs in Lidar Point Cloud Reconstruction Missions

  

(M300 RTK mission, RTK Fix, Zenmuse L1, Terra V4.X, 6 GCPs measured with Emlid RX)

  

  

  

  

Hello Everyone!

  

Since we don't come from the “surveying” field, we have the following questions that we can't really answer. who can help?

  

  

Since Terra V3.9, the import of elevation control points for lidar point cloud reconstruction is supported & accuracy control is carried out.

  

  

A.):

  

Can this be controlled by matching, similar to photogrammetry?

  

Or does the software optimize this internally and the deviation is only visible afterwards?

  

  

B.):

  

The Terra V3.9 notes say:

  

"When importing elevation control points for LiDAR point cloud missions, the output coordinate system and vertical coordinate system must be set to default."

  

  

What means standard: Our “standard coordinate settings” regarding coordinate system and reference height (analogous to the Emlid RX)

  

or

  

the default value in Terra software (WGS84 & Default)??

  

  

  

Even though this is of course a point cloud, we assumed that we could "control" the accuracy with the GCPs.

   

Or does DJI Terra not offer this in this form and we have to carry out the comparison with measured GCPs using third-party software (like TerraSolid)?

  

  

  

Our main problem in understanding is that we lack an overview of the deviation of the L1 point cloud mission with measured GCPs.

  

  

  

Thank you for attempting to explain!

Kind regards

Tim

  

Terra is not a point cloud post processing software.  It is just an interface to merge the laser data and the navigation data, to make it into a LAS or other format.  
Then yes DJI tried to implement some functions, but it remains superfluous and very doubtful in terms of results.
However the free version is more than enough.

One of the best in post processing is TerraSolid software.  Personally I use Global Mapper, cheaper, and the function that will particularly interest you is "LiDAR QC tool".

https://www.bluemarblegeo.com/knowledgebase/global-mapper-24/Lidar_Module/Lidar_QC.htm

LV_Forestry:

Thank`s for the quick and friendly response!
We are currently using the Terra Pro 4.X Version, which “can do a little more” than just converting theLidar Data.

And it is well known that there are significantly better third-party Software for classification.
We actually wanted to choose TerraSolid - now we'd like to take another look at the Global Mapper!

So in your Opinion we should always use "TerraSolid/Global Mapper or similar" by using GCPs to increase the absolute accuracy of the Point Cloud?

And we were hoping that Terra Pro 4.X could simplify our workflow, with the new Functions, for simply structured Projects.

Timmis Posted at 5-23 10:14
LV_Forestry:

Thank`s for the quick and friendly response!

which “can do a little more”
Since there are no option to verify, and shift point cloud position, any feature other than point cloud generation is useless.

So it's not that "you should" use GM or TS to increase precision, it's that you have no choice, because with Terra it's for the moment much too risky, even impossible (no shift function).

It's the same for Terra "magic" functions.
Optimization of precision: quite honestly you have to look very far for the difference. It's a noise reducer, that's all.
Smooth point cloud: This is a big scam, it completely distorts the original point cloud. It's good if you want to make a work of art to print in 3D without too much detail.


I switched to Global Mapper because it's cheaper than TERRA, and it has real features. And the icing on the cake, when the software resists you, there is a technical team who responds immediately and precisely. At DJI it's something else.

For me, the negative points of GlobalMapper are the absence of a trajectory filter, and the difficulty in revoking the license to install it on another PC.


I am not affiliated with the software manufacturer, just a customer. Besides, I invite you to try Cloud Compare which is open source, before investing in anything. Because maybe these features will be enough for you.

CloudCompare - Open Source project

Thank you very much for the further Information & "Destroying the Illusion that it's easier to do"!

Since qualified Support is very important to us, we will probably have to choose between TerraSolid and Globel Mapper... Open Source Solutions are of course also charming - but if you need a specific Solution in a time-critical manner, Open Source is not always the best choice.


Nevertheless, thank you again for all the Information and Assessments!

Tim