Messages

1

General / Automatic point cloud classification

« on: August 15, 2015, 03:00:31 AM »

My study area consists of a ground surface with a lot of sage brush. I successfully used automatic point cloud classification (after messing with the parameters a lot) to separate out the two. I am left with the ground as classified (brown points) and the vegetation as not classified (silver points). My goal now is to to automatically classify the sage brush as low-lying vegetation rather than keeping it as unclassified. However, I cannot figure out how to select all of these points to do so without resetting the entire first classification.

The tutorial skips this step  of a second auto-classification and assumes you would just want to create a mesh from the ground points. I want to keep all the points and end up with a nicely classified point cloud with both ground and low lying vegetation and export that.

Any help is much appreciated.

2

General / Re: Camera altitude vs. GCP Elevation

« on: August 13, 2015, 08:46:20 PM »

Camera coordinates will speed up alignment in "reference" mode. You are right, but you can't mix these coordinates with GCP coordinates unless they are in the same system.
Use in-photo geotags for the align stage and after you're done, add your good GCP and disable camera coordinates by unchek all photos in the referece pane. Change refference system settings to match that of your GCP survey and then update  transformation (optimize) and all your photos will be translated to the ground control points coordinates.

This is very helpful...thank you. I didn't realize you can uncheck the photos. To clarify, here is my workflow with some questions:
1)Align photos using geotags
2)Add GCPs and disable photos in reference pane (uncheck)
3) Optimize the sparse point cloud. Is this the "Optimize cameras" tool?
4) Build Dense point cloud with new optimized sparse point cloud.
5) My goal is to then build a DEM from this dense point cloud.

I appreciate it if you could confirm/clarify this workflow.

Thanks so much,
RC

3

General / Camera altitude vs. GCP Elevation

« on: August 12, 2015, 12:43:40 AM »

Hi all,

As a brief background. I recently surveyed a site with my DJI Inspire 1 at 10m altitude over an area of about 300m X 300m. I created a dense point cloud relying on the camera's known position and selected "reference" before creating the point cloud, so the camera location was used (lat, long, and altitude above ground surface). The results are excellent and now it is time to go back and create a georeferenced model. This is where I have some questions.

Based on other forum topics it appears that the GCPs should be assigned after the initial photo alignment is done. Again, it would be nice to use the camera's known location in this step to speed up processing.  I have dozens of very well located GCPs with elevation values. There is clearly a discrepancy between my GCP elevations (~3000m) and my camera altitudes (~10m above ground surface). When I bring the GCPs in and locate the markers, there is a large error do to this difference after placing the GCP points and "Optimizing Camera."

In a test model I went ahead and ignored this error and proceeded to create a dense point cloud and mesh. I exported the mesh as a TIFF and upon opening the model in ArcGIS it appears it used the marker elevations. Is there a cleaner way to do this? The thing is, I would like to use the camera's known position to help on processing time, but wondering if I need to bring the photos in without spatial data to make sure I am not introducing some error into the model.

Any help/discussion is greatly appreciated.