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Author Topic: how to use markers to set gps and size?  (Read 4293 times)

SB

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how to use markers to set gps and size?
« on: July 09, 2015, 08:06:25 PM »
Hello

I have PhotoScan Pro and I'm trying to scale a model with mesh and texture to the right size.

The model consists of several buildings and some ground between them with different elevations.  I used 2206 cameras (mostly TIFF images with gps EXIF) and some jpg images taken from 4k video (without EXIF). 

The model looks great - dense cloud is wonderful with 61M points.  The mesh looks great with 90M faces.  After 3 weeks of processing (aligning, generating dense cloud) I took a good gps unit with waypoint averaging to the site and took 6 samples of several locations.  Then I placed 15 markers in the model and set the flags in most of the 2000+ cameras.

I have created 10 scale bars using the markers and set the distance in meters.  I also set the GPS lat, long, and alt for 3 of the markers.

The EXIF information in the TIFF images came from a DJI Inspire and contains gps information in WGS.  I also set the marker GPS information manually using WGS coordinates.  I clicked 'update'. 

No matter how many times I click 'update' and/or 'convert' , when I save the model as a obj or ply using 'Local Coordinants', the resulting saved model appears in GeoMagic and Meshlab as being 19mmx51mmx48mm in size. 

Even worse, if I save the model as 'WGS-84' coordinates, the resulting model is only a straight vertical line of a few points that doesn't even appear in my textured model anywhere.


I cannot figure out how to save the model in a way that MeshLab or GeoMagic knows about the correct scale.

The reason I care about having the saved model be the right size is because I'm trying to merge the fantastic Photoscan model I created with point cloud data captured from a laser scanner.  The laser scanner is very accurate and I want to get my Photoscan model the correct size using my gps coordinates and measured markers so it fits together with the laser scanned data.

Can someone help me out with this?

Thank you very much!!

SB


bigben

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Re: how to use markers to set gps and size?
« Reply #1 on: July 10, 2015, 12:22:44 AM »
Try converting to a coordinate system that uses metres as a unit instead of degrees.  UTM.  Think of 10m compared to 10 degrees of lat/long.

SB

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Re: how to use markers to set gps and size?
« Reply #2 on: July 11, 2015, 08:27:46 AM »
Thank you.  This is the right direction.  I tried UTM17 and World Mercator.  Both systems use meters instead of degrees but it did not match the LIDAR point cloud.  I believe the LIDAR point cloud may be using non-geo positions like Local Coordinates in mm. 

I may need to save the points in a xyz file and then scale them by 1000 to convert from meters to mm for GeoMagic.

The suggestion from bigben made me realize that when using WGS84, the points are saved as lat/long/altitude in the file and Geomagic is expecting x,y,z vector data in linear distance from an origin (in mm).  The vertical line was 20M points all along the x axis at a consistant 73.xxxx and on the y axis at a small range of 38.xxxx.  Using Local Coordinates or UTM coordinates converts these degrees to something that works in GeoMagic and MeshLab.

There was one strange behavior- the point cloud is full of stripes when saved in these projected coordinates. The point cloud is great when saved as Local Coordinates.

Should I scale the points in the points file x1000 manually to get the boundaries to be in mm?