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manual tie point

I have a project where the east most GCP only hit the 5 pictures and at the edge of the picture. So I believe I did not have enough overlap. My elevation from the point cloud at this control point is off by 7 ft vertically. If I add manual tie points in this area that has enough overlap pictures Do I have to hit a known x,y,z point as a MTP? I fear that if I just pick a point it is grabbing the elevation from the point cloud which is off 7 feet vertically and then will adjust my other 7 control points which will make them off by roughly 4 feet.

Any help would be greatly advised.

Michael,  

You should not be seeing a 7’ elevation difference between your point cloud and your GCP at the GCP location. 

Did you ReOptimize the model after you marked the GCP’s ?

 

To answer your MTP question:  No, you do not need to know the x,y,z, values for a Manual Tie Point.  Adding MTP’s will help improve the photo alignment and resulting model accuracy.  From my experience, you can never add “too many” MTP’s.  They help improve the reconstruction significantly in problem areas of questionable overlap.  

Just remember you have to give Pix4D the opportunity to Process the changes/inputs you make with GCP’s and MTP’s. 

 

 

Michael,

Ryan makes a valid point that it may also be worthwhile to ensure the quality of the position and orientation of the five images the cover the ground control point. Lower levels of image overlap can, at times, result in a slight misalignment. Pix4Dmapper’s rayCloud editor allows you to address image misalignment by incorporating manual tie points.

Please consider verifying the alignment of the five images by incorporating a manual tie point that is included within the 5 “ground control point” images and a handful of other surrounding images. Image misalignment can be indicated when the manual tie point (yellow cross) does not align with the calculated projection for each image (green cross). In which case, incorporating a handful of manual tie points can address the misalignment and possibly address the vertical discrepancy at the eastern edge of your project area.

Best regards,

Andrew

Shared on behalf of Michael Gray:

“Yes. I even omitted the GCP and reprocessed from scratch. I think the problem is on this GCP only 5 photos hit the GCP and they all were at the very edge. I tried omitting the GCP and adding MTP in this area. However, when I did this it seemed to tie the vertical down but the rest of my GCP’s were off horizontally on the Orthomosaic.”