Getting an image from a URL with parameters
lazarus / 38-Networking and Web Programming

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fapplin · 2015-09-24 21:38

Hi,

I'm trying to use the following function that I wrote to grab an image
created by a web-site and use it as a picture image on my form. I do
get an image, but it's acting like all the URL parameters are being
ignored. Here is the call and the function. When I look at imageName
in the debugger, I see:

'www.astrobot.eu/skymapserver/skymap?type=png&size=800&colorset=0&lang
=en&lon= -78.48&lat=37.33&city=Gladstone&timezone=EST&deco=16399'

If you take the URL and use it in a browser - you'll see an image with
Gladstone in the upper right-hand corner. That is the way the image is
suppose to look. If you strip the URL parameters off:

'www.astrobot.eu/skymapserver/skymap'

This is what I see generated by my program. It's like
HTTPSend.HttpGetBinary is not using the parameters. Does anyone have
any suggestions??

Thanks.

procedure TFormNightSky.FormCreate(Sender: TObject);
var
  imageStream : TMemoryStream;
begin
   imageStream := CreateNightSkyImage(-78, 48, 37, 33, 'Gladstone',
'EST');
   imageStream.SaveToFile('CurrentNightSky.png');
   ImageNightSky.Picture.LoadFromFile('CurrentNightSky.png');
end;



function CreateNightSkyImage(LonDeg : integer; LonMin : integer;
LatDeg : integer;
                                    LatMin : integer; City : String;
TimeZone : String) :  TMemoryStream;
var
  imageName : String;
  imageStream : TMemoryStream;
begin
   imageName := 'www.astrobot.eu/skymapserver/skymap?' +
              'type=png' +
              '&size=800' +
              '&colorset=0' +
              '&lang=en' +
             '&lon= ' + Trim(IntToStr(LonDeg) + '.' +
IntToStr(LonMin)) +
             '&lat=' + Trim(IntToStr(LatDeg) + '.' + IntToStr(LatMin))
+
             '&city=' + City +
             '&timezone=' + TimeZone +
             '&deco=16399';


   imageStream := TMemoryStream.Create;
   if (HTTPSend.HttpGetBinary(imageName, imageStream)) then
   begin
       imageStream.Seek(0, soFromBeginning);
   end;

   result := imageStream;
end;

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derek.john.evans · 2015-09-24 23:15

Small bug in your URL generation code: '&lon= ' << There is a space.

**EDIT** Also, You dont seem to have the protocol at the start of the
URL. ie: http://

As a tip, module-ize your code a little better. eg: Downloading a
TPicture from a URL should be one function. Downloading a TPicture
from Astrobot should be a second function. You shouldn't create
classes (ie: TMemoryStream) in a function and return it. It makes it
unclear as to who (what code) is responsible for it (ie: freeing the
object). I know a lot of people do it, but I dont think its good
coding.

Example: if HttpGetBinary raised an exception, then the TMemoryStream
would not be freed. Usually, to code like that, you would need to
catch exceptions for HttpGetBinary. If an exception is thrown, then
TMemoryStream is freed, and the exception is re-raised.

Simple solution: Don't return class objects. Always pass class objects
as parameters. (Unless, you are writing a class, in which case, the
class should free its objects in its destructor, which is another
story)

This works for me:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses
fphttpclient; procedure PictureLoadFromUrl(const APicture: TPicture;
const AUrl: String);var  LMemoryStream: TMemoryStream;begin 
LMemoryStream := TMemoryStream.Create;  try   
TFPHTTPClient.SimpleGet(AUrl, LMemoryStream);   
LMemoryStream.Position := 0;   
APicture.LoadFromStream(LMemoryStream);  finally   
FreeAndNil(LMemoryStream);  end;end; procedure
PictureLoadFromAstrobot(const APicture: TPicture; const ALonDeg,
ALonMin, ALatDeg, ALatMin: Integer;  const ACity, ATimeZone:
String);begin  PictureLoadFromUrl(APicture,
'http://www.astrobot.eu/skymapserver/skymap?' + 'type=png' +   
'&size=800' + '&colorset=0' + '&lang=en' + '&lon=' + IntToStr(ALonDeg)
+ '.' +    IntToStr(ALonMin) + '&lat=' + IntToStr(ALatDeg) + '.' +
IntToStr(ALatMin) + '&city=' +    ACity + '&timezone=' + ATimeZone +
'&deco=16399');end; procedure TForm1.FormCreate(Sender:
TObject);begin  PictureLoadFromAstrobot(Image1.Picture, -78, 48, 37,
33, 'Gladstone', 'EST');end;   
** EDIT **
I would probably also change the URL generation to a Format()
function. That way, the URL template can be a constant which can be
easily updated.

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fapplin · 2015-09-25 11:16

Thanks for the help and the suggestions. I'm brand new to Lazarus and
Free Pascal (but, a programmer for 30 years in different languages and
platforms). This is being done for a small project on a Raspberry Pi.

Frank