how can i solve this error appears when I try reading position

Question

Unai Bilbao 2021-4-5

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https://ww2.mathworks.cn/matlabcentral/answers/792652-how-can-i-solve-this-error-appears-when-i-try-reading-position

回答： Vinod 2021-4-5

在 MATLAB Online 中打开

Hello:

I am trying to read the position (latitude and longitde) from a data with thingSpeakRead and the next error appears:

Dot indexing is not supported for variables of this type

This is my code from MATLAB Visualizations code:

data = thingSpeakRead(1299642, 'location',true)
lon = data.Longitude;
lat = data.Latitude;
figuregeoplot(lat,lon,'red-*')
geobasemap("topographic")
title("Ground Truth Trajectory")

And this is the output:

data =
     []
Dot indexing is not supported for variables of this type.
Error in Posicion (line 3)lon = data.Longitude;

Someone knows what is happening?

Thank you

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KSSV 2021-4-5

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Just run this line:

data = thingSpeakRead(1299642, 'location',true)

There is no data, it is empty. As the data is empty you are getting error from the next line data.. Check this line alone why the data is empty.

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Answer 1

Vinod 2021-4-5

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https://ww2.mathworks.cn/matlabcentral/answers/792652-how-can-i-solve-this-error-appears-when-i-try-reading-position#answer_667582

在 MATLAB Online 中打开

Your channel is empty, and you are trying to index into an empty array retrieved from the channel. Try this:

data = thingSpeakRead(1299642, 'location',true)
if ~isempty(data)
  lon = data.Longitude;
  lat = data.Latitude;
  figuregeoplot(lat,lon,'red-*')
  geobasemap("topographic")
  title("Ground Truth Trajectory")
end