Post

3 followers Follow
0
Avatar

Linear Mission Map Mission Large Section

This was my first attempt to map a two-lane road with a linear mission and my map is missing large sections. It is also not aligned well. I used only 2 passes but it seemed to easily cover the area I was interested in and provide enough overlap. I merged photos from two separate missions together to create the map. The weather conditions did change slightly between the two flights. The first flight was partly cloudy and flew at ~20 mph. The second flight was cloudier and flew at 13 mph. Any ideas why the map turned as it did?https://www.mapsmadeeasy.com/maps/public/ae613bc64aa443aab0065482280d174f 

https://www.mapsmadeeasy.com/maps/public/ae613bc64aa443aab0065482280d174f

 

Jacob

Official comment

Avatar

Two linear passes is not enough. We recommend at least 3 passes in our Data Collection guidelines but even then you will need to up your along track overlap to make up for the lost coverage.

If you are using 75% across track overlap on two passes you will only bet getting 2X coverage on a stripe that is 3/4 the width of one image. Due to this you would need to up your along track overlap to 85%+ to get enough looks at the scene to reconstruct it. 

Also, the longer the linear mission the more passes you are going to need to get it to process properly. Think of it as a table. Does a table stand on two legs? Nope. 3? Kinda. 4? Getting there. 

The bottom line is you want about 15 looks at everything you want to include in your map. 

Zane

Please sign in to leave a comment.

3 comments

0
Avatar

Lots of good information posted about linear missions, but my test project in MME yesterday (2/6/19) errored out, so I haven't quite got it figured out. I used DJI Pilot app to create a 100-waypoint route; more or less 50 points going north and 50 points returning south; the two passes about 12 meters apart; roughly 1/4-mile in length oneway; flight elevation = 48 meters. I made a copy of that mission, and after moving the waypoints just slightly, I flew that mission in order to have a total of 4 passes, about 200 photos to process. 

My assumption is that - to use Zane's table analogy - my data (table) needs a couple more legs to stand on; I have a north and a south leg, but I need to spread out my passes to the east and west to get two more legs under it.

A client wants nighttime imagery of streetlights in a 5 street by 9 street project area, and I think photogrammetry of the street corridors makes most sense, and ignoring the dark building rooftops within each city block. But I am looking for advice!

Curt Meyer 0 votes
0
Avatar

Curt: Your job failed because you used Windows Photo Editor to reduce the resolution of the images and it killed the EXIF tag information. It also appears that the overlap was about 60% which isn't enough to work for a linear mission. 

 

Zane 0 votes