Craft asset urls not working I have checked all other questions on stack exchange with similar titles and they don't seem to help my situation. 
I have added assets sources to craft CMS. but when uploading I get the following error:


  The error message was: "Error uploading the file:  The file system path "{siteUrl}assets/images/hero-images/" set for this source does not exist."


I am working locally using MAMP. I do not have multiple environments. only local.

the siteUrl variable seems to work fine when used directly in templates. just doesn't work for assets. 

File system path is

assets/images/hero-images/


URL is

{siteUrl}assets/images/hero-images/


General config is set to

return array(

    // Base site URL
    'siteUrl' =&gt; "//projectname:8888/html/",

    // Environment-specific variables (see https://craftcms.com/docs/multi-environment-configs#environment-specific-variables)
    'environmentVariables' =&gt; array(),

    // Default Week Start Day (0 = Sunday, 1 = Monday...)
    'defaultWeekStartDay' =&gt; 0,

    // Enable CSRF Protection (recommended, will be enabled by default in Craft 3)
    'enableCsrfProtection' =&gt; true,

    // Whether "index.php" should be visible in URLs (true, false, "auto")
    'omitScriptNameInUrls' =&gt; 'auto',

    // Control Panel trigger word
    'cpTrigger' =&gt; 'admin',

    // Dev Mode (see https://craftcms.com/support/dev-mode)
    'devMode' =&gt; false,

);


If I open the assets in chrome, this is their file path.

http://projectname:8888/html/assets/images/hero-images/be-inspired-mobile.jpg


This is driving me mad and have checked everything. 

I am using exactly the same config settings as all my other sites which work absolutely fine.
Any help will be really appreciated :)
As per the Craft Docs at https://craftcms.com/docs/multi-environment-configs#environment-specific-variables, add a basePath (or other name) variable to you config. For MAMP, it should look something like:

'basePath' =&gt; '/Applications/MAMP/htdocs/example.dev/public/'

Then in your asset source settings, change File System Path to:

{basePath}assets/images/hero-images/