Boris Skopljak

Tip of the Week #12 - Creating Orthorectified Image for Facade Reconstruction - Using Multiple Stations

Blog Post created by Boris Skopljak on May 31, 2017

Do you projects require facade or vertical wall reconstruction or modeling or vertical surface (e.g. facades)? If so, then you might find this tip being useful to you.

In some projects, it’s impossible to find THE one setup where you can see the whole object without masks (between the instrument and the object you might collect in your photo: people, cars, trees, lightpoles etc…)or because the object is very long (building in a narrow street etc…)so you need to make multiple setups in order to always be in front of it with a good angle.

One way, could be to create several “rectified images” but you might create several planes and so the assembly of these several created rectified images will not be optimal.

In the example below we can see that station 6 provide a good view at the object but some of the areas on the right and left are obscured by trees.

On the other hand, station 4 present a clean bottom left area but a light pole on the right area (which is not good for our purpose).

Images from Station 3 also presents a nice perspective but contains a light pole in the middle.

 

What we suggest now is to use Station 6 as the base of the rectified image (perfectly in front of the building) to create the “Plane” and then use the 2 other stations to fill the missing parts by simply  picking in the Plane the areas that couldn’t be selected previously. We will then obtain 3 rectified images in the same plane that we can then export to a 3rd party Software (AutoCAD, Sketchup  etc…) or in order to generate drawings or directly in TBC.

 

Note: if you know your goal is to create accurate orthorectified images, it’s very important that you do a very good traverse (use correct prisms etc…): this will minimize the overlapping difference between stations. As well, use the same image resolution and try to have your stations as equidistant as possible to the object

In Point Clouds tab > Imagery: Open the “Create Orthorectified Image” ” tool and define a “New Plane Definition”

 

We would like to suggest that you use the “Vertical Plane” method in a similar projects as shown in the image (also make sure that you have points displayed in order to pick the position of the plane). Note also that it could be a good idea to name your plane (useful if you do an area that requires multiple planes creation as well as the Image).

 

Now Pick the 2 corners for the creation of the image (do not select area with masks….) and Define the resolution and select Create.

 

Note: you can check the results in 3D View by hiding everything except the Georeferenced Image (as shown in the view of the newly created Rectified Image below.

Now Back in Station View, select the next station you want to use to complete the building façade.
CAUTION: Be careful that despite you changed the Station view from Station 6  to Station 4, the active station in the “Created Orthorectified Image tool” is still Station 6 (as we didn’t close the tool) so please make sure to change the Station there to Station 4 to avoid issues.

Very important that you use the same Plane Definition than before and simply pick 2 new points to define a new area (select area that wasn’t covered in the previous step) and select Create.

Repeat the Steps for the next Station that will help you to fill the blanks. Check the result of your 3 rectified Images together as shown in the image below. Note that it could be good to equalize the photo in TBC or in the field.

We hope this tip will be useful and make you successful when creating orthophotos within TBC.

Credit this week goes to our Application Engineer, Arnaud Lezennec. Thanks Arnaud!

 

Happy Surveying,

TBC Team

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