UI: Image Position

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來自 Johns Hopkins University 的課程

毕业项目：旅游照片 Web 应用

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Johns Hopkins University

毕业项目：旅游照片 Web 应用

18 個評分

課程 6（共 6 門，Specialization Ruby on Rails Web Development）

In this Capstone project for the Photo Tourist you will implement a Ruby on Rails web application that makes use of both a relational and NoSQL database for the backend and expose the data through services to the Internet using Web services and a responsive user interface operating in a browser from a desktop and mobile device. You will have a chance to revisit and apply what you have learned in our previous courses to build and deploy a fully functional web application to the cloud accessible to your co-workers, future employers, friends, and family. In developing the Photo Tourist web application, you will get to work with different data types and data access scenarios (e.g., fielded data display and update, image upload/download, text search, access controlled information) to provide your users the ability to show off their photos and information from trips they have taken and to seek out photos and information from trips taken by others. Using the application you develop, your users will be able to • Create an account • Upload and download photos to the site and make them accessible to others • Provide descriptions of trips and photos that others can read • Organize photos by location and trip, • Find photos based on location • Find photos based on text searches of descriptions • Locate the place where the photo was taken on a map

從本節課中

Geolocation

In this module you will add geolocation capabilities to the end-to-end application. This will allow your users to assign a geolocation position to images as well as identify the current origin and distance limits for future API queries. You will implement the model and API queries for subjects within this module and complete the UI components within the next module. At the data tier you will add geolocation coordinates to the Image model, make those geolocation coordinates available to ThingImage though the 1:1 relationship between them, implement geolocation queries using the Geokit Rails gem that determine all items within a distance limit from an origin and supply their distance from origin. These queries will leverage custom SQL selects, joins (inner, right outer, and left outer join) and will be encapsulated within ActiveModel query scopes. At the API tier you will implement API service endpoints to geocode addresses and reverse geocode positions into a resolved location using the Geokit Rails gem and the Google Maps Geocode service, implement a persistence cache of geocode results using MongoDB to help stay within free service limits and speed up lookups, enable an API service endpoint to query for subjects (ThingImages) of a certain type, within a distance limit, and dynamically annotate them with the distance from the supplied origin, implement HTTP caching headers for both geocode and subject results. At the UI tier you will implement a geocoder service to lookup a location by (partial) address or position from the API implemented on the Rails server, add geocoding to the Image editor to allow a user to specify the Image's position using an address, build a current origin component to express and retain the center origin and distance limits for future subject queries.

UI: Image Position12:25

UI: Current Origin - Identify Origin by Address7:23

UI: Current Origin - Identify Origin by Current Location12:40

UI: Current Location Override and Error Handling9:28

UI: Distance Limit and Styling10:23

Heroku Deployment6:33

與講師見面

Jim Stafford
Adjunct Professor, Graduate Computer Science
Computer Science, Whiting School of Engineering

[MUSIC]

In this lecture, we will discuss, displaying image position,

as well as assigning image position from a geocoded address, and

then we'll enable caching for $resource.

Now, prior to this lecture, I checked in a few skeletal files for the UI,

and some specs.

And we're looking at the results of a portion of those specs right now.

During this lecture we're going to focus on the following three tests,

the ability to be able to display the location of an image, namely the position,

the ability to put in an address for an image and have it geocoded.

And then, the ability to save that geocoded information with the image for

future displays.

So, if we look at our image, based upon our previous view implementations,

we have no information telling us its location.

But if we inspect the network and refresh the page and display our image again,

we will notice that it's coming back from the service with a position.

We just need to display that at the moment.

All right, so in order to do so, I'll come into the image editor,

come down the page a little, and put in a block of HTML.

We're already receiving the image and

it's available to us in the view model under the item element.

And so, since this is the only thing the image carries with it,

we'll display what we have.

So, if I refresh to the display, we notice now we are showing the longitude and

the latitude.

And if we look at our results,

that's all we were really looking for, display the asisgned position.

Now, what we would like is the user to be able to put in a portion of an address,

have that geocoded, and have the formatted address and

the position available to be used in the image component.

So, what we want to be able to do is to log in as the organizer and

to be able to change this lat and long by plugging in an address.

This next change is not going to be that easy, but

it's not going to be that hard either.

Let's start with the view first, and let me put in a block of code.

So, what we want to do is to be able to put in an input area

that the user can assign an address.

Let me constrain this just a little bit more.

So, if the user can update the image, then we're going to display a label of

use this address, that I'm getting ready to type.

And then we'll have an input area for the user to type in,

which will be assigned to the address variable in the view model.

And the input field will only be shown if they can update.

And then when they click away from the field, we're going to call

a method on the controller to say, can you geocode whatever's in that input field.

And then, when it is geocoded, let's display the format address that comes back

And let's continue to update this area as the user changes locations, okay?

And so, what we need now is a location by address method off of our controller.

And we'll go into the images component in order to add that method.

Now, before we start editing our component,

I want to point out a few things.

If you look in this upper left, I have all ready added a module.

I've all ready added a service, the skeleton of a service, that's going to do

our geolocation and have added those to the JavaScript manifest.

I've all ready injected the skeletal geocoder service into our

ImageEditorController and it's ready to be called,

not necessary function at this time.

So, of course, in order to enable our webpage to call our controller back to

locate by address, we need to add that method.

Well, let's register it right now.

So, we'll go ahead and

add a location by address, just print out a little bit of debug at first.

And what we're fundamentally going to want to do is to call the geocoder

getLocationByAddress, but we don't know all the details yet of how that works.

So, let's us go over in finish implementing that.

So, I've got the shell of geocoder service that's going to call our back-end

locateByAdress, locateByPosition based upon inputs the caller is providing.

So, one of the fundamental things we need are the services that we're going to call,

the resources, and they are off of the APP_CONFIG.server_url and

go to the API/geocode/addresses.

That's what we just finished implementing in the previous lesson.

Now, as far as get it by address,

we just need to call the address as resource, with a get, and to pass

in a query argument of address with a string provided to us by our caller.

And, of course, we owe our caller a result and that'll be a proxy object and

it'll eventually get filled in with the data.

But until it's filled in,

there will be a dollar promise available off of what's getting returned.

And then, for the get by position, we just need to call the positions resource

with a get and we want to pass in a longitude and latitude, which is pretty

much what we're asking to be passed in but all we really care is that there's

a longitude and latitude property, whatever implements the position.

And as with by address we want to return a result.

And again, the result is a proxy that will eventually,

the data will get filled in as the response is returned.

But until it gets filled in, there will be a dollar promise that we can listen to.

Okay, that looks pretty much it for the geocoder service.

Wasn't much to it.

It was kind of easy.

So, if we go back to our location by address, all right,

the details that we're missing is that we could just assign it to location and

then when it does get completed, that location value will be filled in.

However, we want to do a little bit more.

We want to do some behavior when it gets resolved.

So, let's look at the dollar promise.

And implement a call back.

And let's have this call back go ahead and assign the result to the location.

But also, what we want to do is extract the position out of the location and

assign that to the image.

This is what has the lat and the long.

And then, since it's early, let's go ahead and print some debug.

Okay, with that we should be able to get some activity.

If I refresh my display, come back in to my images, if I come in and

say 901 Pratt Street, Pratt in Baltimore, and then click away,

you notice that it went out and did a geocode to our service API.

Found out that the formatted address was really West Pratt Street and

it was in Maryland with a zip code in the United States, and

then this being the geocoded address of that position.

Now, to make things look a little bit more obvious, let's, I don't know,

let's go ahead and put it in South America and now the latitude

should go in the negative direction, okay?

So, we've gone down to negative latitude and we put it some place else, okay?

So, that's giving us a value at this point and time.

Okay, so I'm not saying it's the best user interface in the world,

but we're able to do is take a user from a typed in partial address,

go ahead and fully resolve that into a longitude and a latitude.

So, when they supply an image, they don't have to know everything.

I mean, obviously, we don't want them to have to know the longitude and

the latitude values.

Although sometimes, that's not so bad either.

Better user interfaces can be created, that's for sure.

Just some functionality here.

All right, if we look back at our tests, we're actually passing all three tests

now, because once we put the position within the item that got returned,

then it was there to be assigned the next time around.

And to make some of this a little bit more obvious, I don't have a test for this, but

I'm just going to go ahead and informally put it in anyway.

Then at during reload.

Assuming that we're able to get the G location for the image,

we should be able to also do a G location by position and

be able to fill in that street address.

So, now when we do a refresh,

you notice that the street address comes up immediately.

And if I were to say South America.

Click away, and then go ahead and update the image, clear and

then come back, you'd notice that it's in South America.

And we don't have to necessarily interpret this longitude and latitude.

And then, if we log out, let me see, okay, there it is.

Log back in as Alice.

For a more complete address, update the image.

Log out, hey, where's the railroad?

Okay, there's where it is, okay?

One would argue that this is probably information that we ought to

send over with the image or the thing image, but it's available to be had, okay?

We're looking pretty good on being able to do geolocation based on the image.

And we now have a geocoder service that we can hand information and

say, give us an answer back so we can put onto our view model and pages.

All right, one thing the tests really don't show

is all the work that we did in caching.

What I want to do is demonstrate something right now that isn't going to quite work

the way we want.

So, let me go to the museum.

You notice it went off and looked up positions by latitude and

longitude, and came back with an address.

If I were to clear the image and come back in, you notice it is asking for

that position again.

There's no caching going on.

The same is true as if we look up addresses,

we keep looking things up multiple times.

And if we look in the headers, we see that we're getting an ETag back but

the request headers are not sending anything out.

And the answer to this problem is, is NG Resources implemented in terms of $HTP,

and neither cache by default.

So, we have to tell it.

So, if we come back to our resource, and in the third parameter, and for

the get, we define cache as true.

I'm sure there is more elaborate configurations than that,

but let's implement the default caching, which is all we intend to use.

So, if I refresh the browser, and let me log in as somebody other than Alice.

I've been picking on her images for

a while, and they're all kind of getting into the cache.

So, let me come in as Carol, and she's able to edit the blue blubber jellies.

And you notice, a position comes up the first time we come in.

And if we clear the image and come back in, that position has been cached.

We're not looking that up again.

And to boot, if we come in and do an address lookup,

assuming I haven't looked this one up before, it'll do a lookup.

But if we click in and out, we're not going to get the lookup performed.

If we mung it a little bit, take away the USA to make it look a little different,

you'll see that the call got made.

But as we get that, and we come back with USA again.

If I type that right, that's not going to occur,

if I get rid of the A in the US, we get a look up, okay?

So, it's good to see all that work on the caching on the API layer put

to use on the UI.

And since the cache control says that we can hold onto this for about a day,

it's going to be a while till we go back and hold them again for that value, okay?

In summary, we added image position.

And we displayed a formatted address, after reverse geocoding

the original position and geocoding a newly entered address.

And we saw how $resource doesn't cache by default, but

we could enable that quiet easily to have it honor our ETag caching protocol.

What's next?

Current origin, identify origin by address.

Let's start establishing an overall origin context for our UI so

that components can rally around.

And let's identify the first position to be our origin using an address look-up.

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