Web1.GotText sometimes responseContent is empty

[Marco Perrone]

Hi everybody,

I am triyng to make a simple geocoding app. I use the https://nominatim.openstreetmap.org/ website for this purpose.
As You can see in the attached file I do a web request  for example:

https://nominatim.openstreetmap.org/search?q=Notre%20Dame%20Paris&format=json&polygon=1&addressdetails=1

and in the GotText i wait the response. 

My problem is that sometimes the responseContent is empty, but with the same url in the browser i have a correct answer.

Could be that GotText is fired before the responseContent is loaded with the data?

Best Regards

Thank You

Marco

[TimAI2]

Network/Data/Internet connection not always there? (you can test for this...See here - or there is an extension)

Perhaps setup to display the response Code when you do not get response Content to see what is happening?

[Marco Perrone]

Ok TimAI2 I will check

Thank You 

Best Regards

Marco

[SteveJG]

Use the  call Web1.UriEncode  text                 block ahead of your TextBox1.Text block  (or UriEncode everything in the  join .

Why?  What you type in the TextBox may contain characters outside the ASCII set.  The  UriEncode block converts what is typed into a valid ASCII format by replacing unsafe ASCII characters with a "%" followed by two hexadecimal digits.

The Web page query probably cannot contain space and encoding normally replaces a space with a plus (+) sign or with %20. (your browser link displays  Notre%20Dame%20Paris   not Notre Dame Paris.

Your browser probably does the conversion automatically, with calling the url from App Inventor, you probably have to encode.

Try encoding.  What happens?

Regards,

Steve

[SteveJG]

What exactly are you trying to do with the Nominatim Search Engine Marco?    The url you provide is a link to the search engine, it is not the raw geojson.

The url you attempt to grab a feature collection from while " triyng to make a simple geocoding app."    displays like this in a browser:

 The link does not provide a FeatureCollection in the form needed by MIT's Map component.

Instead of using a Web component;  use a WebViewer to display your search using Nominatim and it will display like this on your device:

Set your Project ScreenOrientation to Landscape and use the following code with a WebViewer

Type  notre dame paris   into the TextBox and press Button2

Is this really what you expect to happen and what you want to do or something else Marco?

Regards,

Steve

[Marco Perrone]

Hi SteveJG,

thank You for your answer I will use Uriencode it will be very useful.
What I am trying to do:

1 The user write an address in the Textbox.

2 I send the request to the nominatin.openstreetmap

3 I receive the answer json formatted ( I use an url like the second provided in my forst post format=json)

4 I use the JsonTextDecode an look up in pairs to retreive the latitude and longitude

5 I use Map to create a Marker and a PanTo to show the address in a Map

The image attached show You what i described and it works, but sometimes (without change the address I have an empty answer, aht responsecode is correct 200)

[SteveJG]

Hi Marco,

A possible explanation of why sometimes you can sucessfully connect to Nomiatim and sometimes you cannot  https://operations.osmfoundation.org/policies/nominatim/  

The solution is probably to provide your own Nomiatim server https://www.google.com/search?q=openstreetmap+nomiatim+server&oq=openstreetmap+nomiatim+server&aqs=chrome..69i57j69i64.12479j0j4&sourceid=chrome&ie=UTF-8 

 I can infrequently access the server using the Web component, mostly I cannot.  When I connect, I get a 200 message; when I cannot connect I don't even receive an error message. Why this happens is probably an issue of limited capacity of the server to process requests. See the top link.

-- Steve

[Marco Perrone]

Thank You SteveJG,

I will use another geocoding service to find the coordinates

Best Regards

Marco