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Improve your projects with the Mosaic Editor – Pix4Dmapper Video Tutorial 6

November 2, 2019

Hello I’m Marc Degroseilliers from Technical
Support here at Pix4D and today we’re talking about the mosaic editor.
Let’s start by saying what is an orthomosaic. The Orthomosaic is a 2D output, a map
which is going to be a stitch of all the images that were taken in the project
but this stitching of all the images is going to be corrected for perspective so
we’re going to use the positioning of the cameras which is information that
the mapper has to be able to correct for perspective and to create a 2D map where
the distances are true relatively speaking. In the mapper there is the
mosaic editor which is going to allow you to edit and to visualize the orthomosaic. It’s available after the third step of processing and it looks
something like this so you can see the Orthomosaic in the main window and you have
some options on the right to create a new region, change the content of this
region and save and export the Orthomosaic When you create a region
there’s going to be a choice where you can choose between the ortho projection
and the planar projection so let’s quickly go over what is the difference
between these two types of projection. As I said when the Orthomosaic is generated
it’s going to take the information from the images and you can blend this
information together and so decide for every pixel what is the color that it
should have. This is done in a way that will where the perspective is going
to be corrected If you insert a region you draw your
region and now you can decide in this region what am I going to project how am
I going to assign the color to the pixels. If you choose the
ortho projection it’s going to use the same algorithm that was used for the
generation of the whole Orthomosaic but it’s just going
to use the images that were selected by the user Let’s say you choose five images you
see these five images they were taken from an angle that was not too
large so they were more or less on top of the scene and if I use just these
images maybe some of the artifacts that I’m saying in the Orthomosaic are going
to be reduced so I’m going to use the same algorithm the same way to stitch
the images but just with these five images and then that can improve the
result for this region. The alternative is to use the planar projection. What
does the planar projection do? It just takes the region and it’s going
to project the content of a single image onto this region now what this means is
that since this was this is a projection from a single image the perspective is
not going to be corrected and therefore the distances are not going to be true. Why would you want to do that? Well let me give you an example: let’s
say you have a neighborhood and you have a few houses and this is
the main point of interest of your project but there’s also a forested area, let’s say a parc next to next to the neighborhood and the main point of
interest are the few houses but you also want to include this forested area
in your project however because of the geometry of the trees in the Orthomosaic you see some artifacts maybe some doubling of the leaves or something like
this and you want to correct for this but this is not the main region of
interest so maybe you don’t care so much that the distances are not true so then what you can do is you can draw
a region around these trees and then you can do a planar projection
with an image that was taken more or less above the tree and therefore I mean
these distances are not going to be accurate in this region but it it might
create a more visually pleasing result and this is all you care about for this
particular area of the project. So this is one
good example of when you would want to use the the planar projection.
Let’s move on to a point which is a little bit tricky with the Orthomosaic which is saving the Orthomosaic because there’s both internal copy and there’s the exported
geo tif that you can use in the third party software so let’s see what happens.
When you draw a region and maybe you draw a few regions and you want to save
the changes that you made in Pix4Dmapper. Then you’re going to click Save and what
this will do is that it will overwrite the internal copy of the Orthomosaic
but it will not change the exported geo tif if you want to see these changes reproduced on the exported geo tip then you will need to click the export
button that’s the difference between save and export is that it will affect
either the internal copy on which you’re working which is the internal copy of
the inside the software and then if you use export it will re export the Orthomosaic so then it will modify the exported Geo tif.
In the Orthomosaic editor there’s also a visualization option and this will give you some
information about the pixel distribution the distribution of the value of the
pixels and it will also allow you to analyze this information either for the
whole Orthomosaic or just for a single band. Let’s go now inside the mapper
and let’s see how you can add the region select the images that are going to be
used in the planar or ortho projection and let’s see how to do this inside the
software. Here is my Orthomosaic and in the mosaic editor here (let me
show you how to add a region) so let’s go maybe to the side of the project where
typically there are less images and less overlap and so you can see more artifacts. Here you see I have the
street and there are some some blobs and here the trees didn’t get reconstructed
quite okay and let me draw a region and I finished the region by right clicking.
Now I can choose a planner projection and already you can see that
the your mosaic looks much better this is for visual reasons. Now I’m
going to leave this region and maybe I show you how to draw another one left
click and then right click finish and then I choose orthoprojection. This takes a
little bit longer because the mapper has to produce the ortho projection let’s
say I picked these three images and now the Orthomosaic is
generated using only these three images. If i delete it we see a slight
difference so that’s how you can edit the Otrhomosaic after generation in
order to improve its visual aspect. I hope this video has been helpful and
i’ll see you in the next video

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