The interpolation result heatmap has abnormal deformation on the x-axis

[StarWish365]

Hello, I encountered some problems when using your open source interpolation API, as shown in the figure below:

In theory, the interpolation result should present circular hot spots around the data points, but in my drawing results, the hot spots are distributed in elongated ellipses along the x-axis. My drawing is based on the Mapbox API, so I want to confirm whether this problem may be related to the coordinate system I use?

I have carefully checked the parameter settings of the interpolation calculation and found no obvious problems. Have you encountered similar situations? Or do you have a recommended solution?

Thank you very much for your help!

[Rylern]

I want to confirm whether this problem may be related to the coordinate system I use?

Do you use the Mercator projection? Only this projection is supported

[StarWish365]

I want to confirm whether this problem may be related to the coordinate system I use?

Do you use the Mercator projection? Only this projection is supported

Yes! Mercator projection is the default projection and I didn't change it. The problem still exists.

[Rylern]

So I think this is related to the nature of the IDW formula. If the range of latitude of your points is bigger than the range of longitude of your points, then you see these elongated ellipses along the x-axis.

For example, here is what it looks with 5 points that have the same latitude:

The ellipses are elongated along the y-axis.

And here is what it looks with 5 points that have the same longitude:

The ellipses are elongated along the x-axis.

I'm not sure if this is the correct explanation though. Does it make sense to you?

[StarWish365]

Yeah I think it makes sense. Because I tried setting my map size to a 1:1 aspect ratio and the heatmap stretching stopped happening. Thanks a lot.

[StarWish365]

Hello, I found that whether my heat map is stretched or not is related to the map size I set. When my map‘s width is larger than height, the heat map is stretched on the x-axis, and when the height is larger than the width, it is stretched on the y-axis.

My current solution is to set the map width and height to 1:1. Do you have any solution so that I can get a normal heat map on a non-square map?

[Rylern]

You're right. I spent a few days thinking of a solution and I came up with a very simple one. Could you try version 1.6.1 and tell me if it's good for you?

[StarWish365]

You're right. I spent a few days thinking of a solution and I came up with a very simple one. Could you try version 1.6.1 and tell me if it's good for you?

Hi, I tried the new version and it works perfectly now. Thanks!