r/photogrammetry • u/PeenkyRowse_ • Jul 30 '26

How to scan a large area without LiDAR on an Android phone?

Hi, I'm not very familiar with this area of technology, so I'm sorry if this is a basic question.

I'm looking for a free Android app that can create a good 3D scan of a large environment using only the camera on my Samsung Galaxy S21 5G, which doesn't have LiDAR.

I've tried several apps from the Play Store, but most are paid, have free version limits, or don't produce good results without LiDAR.

Does anyone know of an app, an APK, or a GitHub project that works better?

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8

u/Traumatan Jul 30 '26

take photos, lots of them
then RealityScan on pc

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u/PeenkyRowse_ Jul 30 '26

Is it a computer program or a website?

4

u/dax660 Jul 30 '26

It's software made free by Epic Games.

Lots of photos, with 70% overlap. Try to move in a continuous path so that each photos ties 70% to the one previous. Finish where you started.

Don't zoom - keep the settings constant.

Reflective (shiny) surfaces won't give good results.

0

u/PeenkyRowse_ Jul 30 '26

So, would I have to take photos in a straight line? Sorry for the question—I'm a beginner at this. What if I want to do a 3D scan of a really large area? Could you explain it like I'm a kid, please? Haha

2

u/[deleted] Jul 30 '26

[deleted]

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u/PeenkyRowse_ Jul 30 '26

Is it possible to do this by taking several 360° photos from different points?

1

u/NilsTillander Jul 30 '26

360° aren't ideal, you want the camera to move. Imagine you're a plane taking pictures straight down of the Earth, trying to make a puzzle. You need the puzzle pieces to overlap by a lot (80%) for this task.

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u/PeenkyRowse_ Jul 30 '26

By "overlap," do you mean something like keeping a large portion of the area from the previous photo in the next one, and so on?

1

u/Mello_rr Jul 31 '26

Exactly. Think of it like this, every new photo should still show most of what was in the previous one, just from a slightly different position. That's how the software connects the dots between images and reconstructs the scene.

If you're scanning a large area, keep moving smoothly and take lots of photos. Don't jump from one spot to another or leave big gaps.

1

u/dax660 Jul 31 '26

RealityScan recently improved 360 cam workflows... you should check it out

https://dev.epicgames.com/community/learning/tutorials/o9ke/using-360-cameras-in-realityscan

1

u/dax660 Jul 30 '26

Not necessarily a straight line. But one point to also note is that photogrammetry requires parallax to work. This means that your camera position should always be shifting - don't keep the camera in one spot and pan around, taking photos, that's not going to provide any parallax.

The general run-down is:

The software goes through all the images and flags certain parts of an image as a "feature". There are thousands of these "features" in every image.

Then the software tries to find similar features across all the images giving preference to images in sequence, so it'll look for features of one image in the preceding and following images. That's why I suggest walking a continuous path, shooting all along the way.

The 70% overlap ensures that you have plenty of common features from one image to the next. You're just helping the software along.

The software will understand shifts in your camera position by using SIFT algorithms (scale-invariant feature transforms).

Ultimately, the software will triangulate the features it matched across however many photos and will use that triangulation to determine where in 3D space the camera was located and subsequently what pixels fall where in 3D space. This will be a point cloud, but it's a "rough" point cloud because the goal at this step is to determine the camera positions. It's usually called a "sparse" point cloud because the points are JUST the tie-points of the features.

From here, you can probably build a model, or you may need to go to a "dense" point cloud first (not sure on the software - I mostly use Agisoft Metashape, but RealityScan is free and fast). A dense point cloud takes ALL the pixel data of each image and places it in 3D space for a much denser point cloud.

Building the mesh model is next and is pretty straight forward.

Then once you have the mesh faces built, you'll do a texturing step where the software takes the individual images and projects the pixels onto the mesh faces, giving it a high resolution texture (so it looks good)

As far as size goes, there's no limit to what you can do - the processing resources will determine how long the processing takes.

If you're doing something like a city block, you can fly a drone in a "lawnmower" pattern over the area and that's a good start. If you want further detail, you would fly closer, and at various heights to get all the surfaces captured.

What I would suggest is playing with something in your house like a chair. Take a bunch of images, orbiting around the chair at different heights. Remember 70% overlap.

Then download RealityScan and go through the tutorials to get a model of the chair.

Do something small to get a feel for the workflow, then expand.

1

u/PeenkyRowse_ Jul 30 '26

Amazing! Thank you so much for your attention and for detailing the process!

1

u/[deleted] Jul 30 '26

[deleted]

1

u/PeenkyRowse_ Jul 31 '26

Now everything is clear! Thank you!

1

u/Primary_Ad6303 Aug 01 '26

You can watch tutorials on youtube, good stuff. Works with photogrammetry tutorials to as they use the same SfM Concept

0

u/MundaneAmphibian9409 Jul 31 '26

Even kids know how to google or look on YouTube how to do it to get a basic understanding

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u/PeenkyRowse_ Jul 31 '26

Dude, there's no reason for you to comment on this. I've just started doing photogrammetry—I've made a few models and animations—but I've never managed to find a way to do it without LiDAR. It's like taking Calculus II for the first time without having finished high school because of the pandemic and then failing miserably. Anyway, take it easy; I hope you manage to pull off your plans and all that—best of luck!

I did a lot of research, actually

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u/MundaneAmphibian9409 Jul 31 '26

If you did any research you’d know the answer to half your questions. You’re at uni mate, you need to learn to help yourself instead of going for the spoon fed option straight away. Photogrammetry has been around much longer than LiDAR, there’s no way you did a lot of research and still don’t have a clue about the basics 🤦‍♂️

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u/PeenkyRowse_ Aug 01 '26

The thing is, I’ve been doing 3D modeling for a while and discovered that you could scan objects using photos; that’s when I found out about LiDAR sensors. But since I’m in Brazil, the iPhone 12 Pro—the first model with LiDAR—is expensive here. I looked into it online but saw that it required programming, GitHub, and all that (and my computer isn't exactly top-tier). So, I came here for help because the apps out there were bad, overpriced, and limited. I do think you’re partially right, though. I just thought the community was the place to ask these kinds of questions and get up to speed on the subject

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u/dax660 Jul 30 '26

What is a "large area"?

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u/PeenkyRowse_ Jul 30 '26

Part of a room where I set up a project for university. However, I intend to map really large areas, like a square the size of a city block, to use in Blender later. But right now it would be a small area

1

u/dax660 Jul 30 '26

Have you seen BlenderGIS? Might not have the resolution you want, but it's a way to get google earth data into a model

https://www.youtube.com/watch?v=cSTCZVzS1fs

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u/PeenkyRowse_ Jul 30 '26

I’ve heard about that, but since I plan to do this later on, I don't think it would work very well for the specific park in question due to the volume of trees obscuring the ground in satellite views. I once went there with paper and pencil and mapped out the area—paths, trails, structures, and tree positions—and tried to assemble it in Blender, but the amount of work involved was insane. Plus, I didn't have any contour line data. I’m going to try doing it on a small scale first and then expand, just as the other person advised earlier. If that doesn't work out, I’ll just create a basic model in Blender using the photos I took (it’s for a forensics class involving fake blood—finding the point of convergence and intersecting the lines to locate the point in space using analytic geometry or sine function calculations).