Time for some shameless self-promotion.

Uploading your 360 imagery to Google Street View can be a great promotional tool for your business or project.

Federico, our chief photographers, knows this well.

In embedded Street View <iframes> you can see the photographers name in the top left and top right.

When clicking the “View on Google Maps” link, you’ll also see the icon associated with the Google account. In this case, a headshot of Federico.

Federico Google Maps headshot

Sometimes you want something more striking. Or if you’re not using Google, something that stands out in place of your name.

A custom nadir is perfect for achieving this. What is a nadir? This post explains more.

Google allows custom nadirs in 360 imagery, as long as they follow their branding guidelines.

Some manufacturer or propriety apps will allow you to do this in their own tools too.

This post explains how the processing of adding a nadir works, and how to do it yourself for free.

For those that have lots of photos to tag, we’ve built a free piece of software that will help – more on that at the end of this post.

Equirectangular and Cartesian projection

The worlds most famous equirectangular projection – the world map.

World equirectangular projection

As a child, I remember looking at Antarctica on a map and thinking it was huge, until a teacher explained it was ‘stretched’ as an equirectangular projection.

If you’ve every looked at a equirectangular projected 360 photo you will have clearly seen how distorted it is at the top and bottom of the image, but less around the center. Here’s why…

Equirectangular graph

Cartesian images are taken by camera sensor (including all of the sensors in your 360 camera). They’re less hard to get your head around. They produce ‘flat’ images on a 2D Cartesian plane (x,y). Here’s a 3D Cartesian plane with (x,y,z axis).

Cartesian 3D graph

Your logo, is a Cartesian image / projection.

Simply overlaying this as a nadir or zenith (bottom or top) on a 360 equirectangular projection will cause distortion issues.

To solve this problem, you first need to convert the proposed nadir image into an equirectangular projection and adjust to match the width of the original panoramic image for it to display without distortion.

How to create your own nadir

Now you understand the problems associated with overlaying Cartesian projections on equirectangular projections, here’s how to process a nadir to display correctly in a equirectangular image.

Step 0: Download GIMP 2.10 (other programs are available)

You can overlay nadirs on 360 photos in most graphical programs, including Adobe Photoshop.

In this example I’ll us GIMP because it’s completely free and easy to use.

You can download it here.

Step 1: Create a nadir image

Aim to create a logo with a large resolution. For 4K images 500 pixels x 500 pixels will suffice.

For simplicity, the process below will always result in a circular nadir, whether you use a circular logo or square logo to start with.

If you use as a circular image for the nadir, make sure to use a transparent background and to save as a .png image.

Here are some example nadir logos.

I’ll be using this one…

Trek View Circle Nadir

Step 2: Turn the nadir image into an equirectangular projection

GIMP create equirectangular nadir polar coordinates

Rotate the image 180 degrees (Image > Transform > Rotate 180).

And create the equirectangular projection (Filters > Distorts > Polar Coordinates…).

In the Polar Coordinate options select:

  • Circle depth in percent: 100
  • Offset angle: 360
  • Map backwards: false
  • Map from top: false
  • To polar: false

And select OK.

Step 3: Overlay equirectangular nadir onto equirectangular photo

Now move to your equirectangular photo in GIMP and create a new layer on the image (Layer > New Layer).

Copy the square equirectangular nadir you’ve just generated in GIMP and paste onto the new layer created on your equirectangular photo.

Now we can adjust the width of the nadir to the width of the photo so that it appears as a circle again when loaded in a 360 viewer.

First find the size of the 360 photo (Image > Image Properties).

The photo I’m using is 5760 x 2880.

Now we can scale the nadir. First make sure you are working on the correct layer of the image, the one with the nadir in.

Add equirectangular nadir to equirectangular photo

Then scale the image so that the width of the layer size matches the width of the equirectangular photo. Make sure to ‘unlock’ the aspect ratio, otherwise the height of the nadir will be increased by the same ratio.

You can also adjust the height of the nadir. The greater the height of the nadir overlay, the more area at the bottom of the image will be covered (the larger the circle, in the example, will be). As a general rule a nadir height of between 5% to 15% of the photo image height looks best.

Note, if uploading to Google Street View:

For 360° photos, superimposed content must be limited to either the zenith or nadir (top or bottom 25% of the equirectangular image), but can’t be present in both.

Once adjusted, click scale. The overlaid nadir should now be as wide as the photo.

All that’s left to do is to snap the nadir to the bottom and left of the photo (Tools > Transform Tools Align).

Now set it so that your nadir layer is aligned to your photo layer (target layer):

  • Align left edge of target
  • Align bottom edge of target

Step 4: Export the result

Save the image (Export > Save).

Now open up the image in your favourite 360 viewer to check if it’s the result you’re expecting. Here’s what mine looks like:

Nadir Patcher (automated processing)

Using GIMP is perfect for one or two photos. For a tour of hundreds of 360’s, you’re going to need something a bit quicker.

That’s where Nadir Patcher comes in.

It’s a command line Python script that 1) takes logo file, 2) converts to equirectangular image, 3) transforms to desired size, and 4) overlays on-top of one or more equirectangular photos or videos as a nadir.

It’ll brand 100’s of 360 photos with custom nadirs in under a minute.

Download it for free here.

Post author

David Greenwood

Founder, Trek View

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