Messages

1

General / Flir Thermal Model

« on: August 13, 2016, 11:14:39 AM »

Hi All,
Having a problem. I am using a Flir Vue Pro to shoot some aerial photographs of archaeological sites. I have seen photoscan be used by other people, but when I try to run it, it just can't seem to produce an alignment. It is saying that the cameras have been aligned and I can get a point cloud of around 60 000 from them using highest settings. It will show points on the screen but not a scene as such, nor camera locations.

The Vue Pro is low res (640 × 512) and I am filming scenes as jpeg files as black/white hot. I have plenty of overlap and am taking hundreds of photos.

Can anyone offer any advice as to settings? I also have a regular photographic model of the same area and I have multiple GCP's. I am just not sure if its the fact that these black/white images are just not different enough, or if I am messing up something in processing as I have seen people creating models from thermal before including in B/W.

Any help would be amazing!

2

General / Accuracy of measurements

« on: October 24, 2015, 08:18:35 AM »

Hi All,
I am an archaeologist and I am testing photoscan for the creation of ground plans. I just want to make sure I understand one aspect of it.

One test I did was to place a L shaped piece of metal with 3 known distances on it(quite small, like 0.35m and 0.55m). I use the right angle of the markers on the L in order to produce an orthophoto of the area using them as the horizontal and vertical axis, in order to get a perfectly flat birds eye view.

Anyways, I input the distances into photoscan, create scale bars and get a minimal error of a few mm.

Now to test the accuracy of just using these two points on the L piece, I placed a few control groups of marks anywhere from 2-5m away. These were either 1 or 2m in length.

What I want to know is- what is the error produced when just using the L shaped piece with 3 measurements. Obviously as you add more scales, it gets more accurate.

I think if I create markers for my control group points, then create scale bars and enter the distances (1 or 2m), it will provide me with the error. I just want to check that I do not UPDATE this, as if I did it would modify the error with all the scale bars correct?

So just to get the error using the 3 points on the L, enter distances and hit update. Then to get errors of my controls enter distances but do not hit update. Correct?

Thanks in advance for what is clearly an easy question- I just want to make sure.

3

General / Re: Archaeological Planning using Photoscan- without GC

« on: March 26, 2015, 07:13:03 AM »

Hi All,
Thanks for the advice. So I have been tinkering around with a few models I have. They are of archaeological trenches, and have pegs, which I know the distance between. These pegs have been placed in with a total station, meaning despite changes in elevation, they are set distances apart ie 5m if you were looking at it from a orthoview. I do not have the X-Y-Z coordinates though.

What I did was added each peg as a marker with no xyz values and then created 5 scales and entered the distances I knew were between them. They circled the trench on atleast 3 sides. Ie think of a square and I knew the distance of the three sides. On one model, these were all at different height levels.

When I produced the model- I noticed that not the FRONT view but the Back view seemed to give a pretty vertical orthophoto. I saved it as an ortho and then in photoshop overlayed two different plans of walls in the trench and both of them aligned pretty much perfectly.

Now I am fairly new to this so if someone can explain how this happened-ie how Photoscan worked that out? Is this, as I knew the horizontal distances between each marker that PS could use those to work out what was flat/verticle?I would have thought once the model was created and became 3d, that measurement of 5m would be very wrong as the pegs are vertically at different heights. Basically, many of you said something similar below ie Thomaxs,Alexey, Geo.
I imagine if I made a model with pegs that were 5m apart, but that was just measured by tape and wasn't all at the same height- it would be askew.

So in order to replicate those without total station pegs, as many of you have said, if I was to set up several markers which are horizontally the same height, and whose distance apart I knew, it would produce a completely vertical. Say a few flat scale bars 1m wide with markers on either end, that I use a spirit level to make sure is perfectly flat. I imagine if I used two or three of those, they all would need to be the same height?

As Thomas said, if I used an L shape piece, say 1m by 1m, with 3 points(one on each end and one in join) that was nice and flat, even on a large model of say a building that was 20m by 20m, as long as its in model, I could use it to make sure it was flat even though its quite small? Or is the further apart the points, the better? Does that make sense?

Sorry, for no doubt stupid questions, I am just trying to wrap my mind around it. Would hate to do something and find that I messed it up and that the archaeoloy was then destroyed and I couldn't check it.
Thanks so much for all your wonderful help.

4

General / Archaeological Planning using Photoscan- without GC

« on: March 25, 2015, 05:45:39 AM »

Hi All,
I, like a number of folks here, am an archaeologist and I have used PS to create models of archaeological remains- although I am fairly new. I am after a bit of help with a workflow for something slightly different.

Here is the situation- on a couple of projects I have been on, I have created top down plans of archaeological features using photoscan and a total station to give me GCP. Basically, I create orthophotos which I trace off in adobe photoshop or illustrator. The plans end up looking like this(http://www.twoatlarge.com/illustrations/tower_1.jpg) nb: thats not my plan and just shows what an archaeological plan will look like if you don't know. I will sometimes make models without a total station but will mark on the stones a series of measurements ie I will put stickers on that are 1m apart to give me a scale.

I have been asked to look into using this sort of skill on things such as rescue excavations, where we have a day or two to dig an area and require a plan, but often not the time to do this properly. The big issue with this is that generally there are no total stations or anything to give me x,y,z coordinates. I can us a theodolite to get heights(z) though.

What I need to do is to produce an orthophoto that is a perfectly vertical/birds eye view of the building, wall , feature etc like the example above. What I am curious about is if anyone can suggest a way I can get this perfectly vertical orthophoto without just trying to guess what is vertical? With GCP points from a TS- it obviously knows what is flat and produces a nice orthophoto, I just cant work out how to do it without GCPs.
 I would then use stickers or markers at set measurements to provide scale so in that sense it's fine.
 I am using PS Professional.
If anyone can offer some advice, or if there are any archaeologists out there doing this, I would love to hear from you.
Thanks
Hugh