Scaling GEOGRAPHICLOCATION imagery to align with its own GPS coordinates

[trueravenfan]

Forgive me, as I'm sure this has been asked somewhere, but I can't a post of find someone doing quite what I am doing, so here it goes...

I am on a quest to draw lines on top of a satellite overlay, in order to export those lines to use for their GPS coordinates. All similar posts I'm seeing seem to be for people using meters/feet/etc north/east of a given datum, which is understandably the normal way of doing things, but not what I need-- I need the pure GPS coordinates to be the coordinates of the drawing itself. This is to say that if I create a point in my drawing by typing point -81.800882, 24.550632, I expect that point to (a) be located at drawing coordinates of -81.800882, 24.550632 (duh), and (b) that point to be located on top of the Key West Lighthouse (whose real-world GPS coordinates are 24.550632, -81.800882) in the imagery.

I have read things about using Army Corps of Engineers "CorpsCon" to georeference my drawing, but this would be counter to my use, as I directly export the lines in my drawing via DATAEXTRACTION. If the drawing's coordinates were in a properly referenced northing/easting situation with whatever correct CRS, I understand that I may be able to get the same result, but my question is if I can avoid all of this. I'm a light student user, and do not intend to delve deeply into the world of CRSs, I just need to scale the imagery this one time. My approach may not be conventional, but it is within my limited capabilities, and practical for my use case. It's important to mention that it is of no value to me to have my lines drawn in a proper projection-- circles do not need to be round, straight things are fine to appear curved, etc. I just need to trace some shapes and extract their GPS coordinates en masse, so I don't care how they look in the drawing, only that they hold (and subsequently export) the correct values.

Here is what I've done:

• "GEOGRAPHICLOCATION" --> "From Map"
• Placed pin at 24.550632, -81.800882 (elevation "0", real elevation is about 5ft)
  • AutoCad appears to round this to "24.5506, -81.8009"
• Selected CRS of WGS84 Pseudo-Mercator (ESPG:3857), which states unit "Meter"
• Selected drawing Unit of "Meter"
• AutoCad asks for a location to insert, I provide "-81.800882,24.550632,0"
• AutoCad asks for north direction angle, I provide "90"

This results in the imagery aligning correctly, but not being scaled correctly, as evidenced by my (verified) GPS data of some geography (shown in white). I assume this to be because it expects a length of 1 in my drawing to equal 1 meter, which it does not-- it equals one degree of latitude or longitude.

Fiddling with the CRS and/or Drawing Units can lessen the ridiculousness-- here's the same CRS with drawing unit "Kilometers", and (whaddya know) the imagery is about 1000x as zoomed in. It's still correctly aligned, but still incorrectly scaled. The scale is far closer, but this is the max unit I can use, and regardless this is clearly not the correct approach anyway.

Is there some way I can align this imagery such that the GPS coordinates of the imagery align with decimal GPS coordinates within my drawing as I intend? It seems fairly inconceivable that something this conceptually simple wouldn't be possible in something as powerful as AutoCad, yet I can't seem to figure out how to align/scale the imagery to this effect.

Thanks in advance for the help of those who (unlike me) actually know what they're doing. And sorry if my methodology makes you cringe! 

[Ed.Jobe]

What is the coordinate system of the data you are inputting? Set your coordinate system to that and (I'm assuming google) map layer will be scaled to the assigned coordinate system.

[trueravenfan]

Hi Ed, appreciate your reply.

It's via the normal imported-by-AutoCad "GEOGRAPHICLOCATION" command, which appears to use Bing Maps. Internet searches indicate that both Google/Bing uses the normal "WGS84 Web Mercator (Auxiliary Sphere) [...] ESPG:3857". I have tried ESPG:3857 unsuccessfully (in fact, it's the one used in my previous screenshots). I also found that the Google/Bing Maps APIs use ESPG:4326, but 4326 does not appear in Cad's list of selectable coordinate systems:

Following some further research, I'm now 99% confident that it's 4326 I need-- the linked post says the APIs "use lat,lon coordinates [...] in EPSG:4326 (aka WGS84)". Additionally, examining the ESPG specification shows that ESPG:3857 (what I'm currently using) uses value increments of 1 to represent "1 meter", while ESPG:4326 uses value increments of 1 to represent "1 degree" (what I want).

So the remaining barriers to getting the GEOGRAPHICLOCATION command to correctly scale the imagery are these:

1. I need to somehow add "pure" WGS84 (ESPG:4326) to the list of selectable CRSs.
2. I need to select a "Drawing Unit" of degrees, or otherwise indicate to AutoCad that the drawing units are exactly the same as the units of the imagery.

[ChicagoLooper · Accepted solution]

You are trying to pound a nail with a brick. I'm sure you can do it, but just because you can, doesn't mean you're using the appropriate tool for the job. Your dataextraction operation will provide numbers but those numbers may be meaningless without correlating them to their appropriate State Plane x/y values.

You need to take this to Map 3D (or Civil 3D) which can read, understand, and produce coordinate geometry. Your drawing will be (should be) projected to Florida State Plane using feet and your GPS coordinates are geographic in decimal degrees. The GEOGRAPHICLOCATION from map operation that you have used is not to do what you want. While you can input lat and long, it cannot correlate those GPS coordinates with State Plane unless you use third party software. Map 3D however, has enough horsepower to do it all.

Your lat/long 24.550632, -81.800882 has x/y coordinates 389967.558408, 79734.819343 when using FL83-EF (EPSG 2236).

Using Map 3D the Lat/Long is correlated with Florida State Plane-feet.

If you are trying to scale aerial imagery, there are easier ways to do this, way, way easier. If you are trying to scale it  to align with its own GPS coordinates, as the title to your post suggests, then there is no way around it, you must correlate the lat/long decimal degrees with the State Plane x/y feet. If you are trying to pull out the lat/longs from your finished drawing, vanilla Cad doesn't have the capability to determine lat/long. If you are planning to extract Florida State Plane x/y coordinates in units of feet  from your finished drawing you can't do that until you scale it, and scaling it may require third party geospatial program e.g. ArcMap, Global Mapper or QGIS. Of course, Map 3D and even Civil 3D can do it too.

[trueravenfan]

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@ChicagoLooper wrote:

You are trying to pound a nail with a brick. I'm sure you can do it, but just because you can, doesn't mean you're using the appropriate tool for the job.

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Fair enough. And yes, "trying to pound a nail with a brick" is exactly what I was trying to do, and I understand the inherent difficulty of finding answers when I'm not even doing things how they're normally done, so I appreciate the candor and guidance. 

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@ChicagoLooper wrote:

Your dataextraction operation will provide numbers but those numbers may be meaningless without correlating them to their appropriate State Plane x/y values. [...] Your drawing will be (should be) projected to Florida State Plane using feet and your GPS coordinates are geographic in decimal degrees. The GEOGRAPHICLOCATION from map operation that you have used is not to do what you want. While you can input lat and long, it cannot correlate those GPS coordinates with State Plane unless you use third party software. Map 3D however, has enough horsepower to do it all.

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The trouble is that the coordinates from the dataextraction must indeed be specifically the GPS coordinates, and not State Plane x/y values. I assume you consider them to be possibly useless because they will appear distorted when plotted on a flat grid-- I should clarify that I am using the extracted coordinates to import into external software, which plots the GPS coordinates in an appropriate projection (which is why I want the raw GPS, and not the projected northing/easting values). Thus, I don't care what they look like in cad, as long as they have the correct lat/lon values.

Disappointingly, it sounds like it is probably not possible in stock AutoCad, so I will try using AutoCad Map 3D to make my tracings instead. Because I eventually need them in the original AutoCad drawing, I am planning the following workflow:

1. Use AutoCad Map 3D to generate the tracings (with imagery aligned via one of the Florida State Plane CRSs).
2. Export the GPS coordinates of the lines I've traced to a file.
3. Import the lines into the original AutoCad drawing and save.
4. Proceed with the dataextraction operation (with multiple layers together).

I will report back when I make progress!

[ChicagoLooper]

You can still do it from vanilla AutoCAD but you have to know what AutoCAD needs when you run through the procedure. Like a lot of AutoCAD, it is not clear what you need to provide as input. (Warning: Many users don't follow the sequence and is the reason why they believe the Geolocation command doesn't work. Trusts me, it works.) If you understand what is required and compare it to how AutoCAD asks for it, it gets confusing. Follow these steps and you'll be fine.

Note: Map 3D/Civil 3D is like that 'office supply store.' Both M3D & C3D programs operate like they have an EASY button. Vanilla Cad doesn't have an easy button.

Using your lat/long coordinates here are the steps (don't forget your long is negative and needs a minus sign):

1-Go to http://www.earthpoint.us/ (Click State Plane)2-Select Florida, State Plane, East Zone, enter your lat/long, then CALC.3-The corresponding State plane, in units of feet, will be shown, Write it down.4-Geoloc tab>Location panel>Edit Loc>From Map. Then enter lat,long like shown. (You are defining a specific 'point' and not an address.) Then click search which is the magnifying glass icon.5-Do not pan or zoom. Go directly to 'Drop Marker Here' and click it.6-for Coordinate System choose FL83-EF (or any other 'appropriate' and 'applicable' CS), then NEXT.7-On command line, enter x,y coordinates of the State Plane Calc that you wrote down from image-3. Hit ENTER. Now turn on Bing imagery.

[Pointdump]

Erik,
"I am on a quest to draw lines on top of a satellite overlay, in order to export those lines [via DATAEXTRACTION] to use for their GPS coordinates."
I'm curious. What are you going to do with the extracted lines? GPS Routes or Tracks?
Dave

[trueravenfan · Accepted solution]

So, I've been able to get the results I needed, and it did indeed require AutoCad Map 3D. But real quick...

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You can still do it from vanilla AutoCAD but you have to know what AutoCAD needs when you run through the procedure.

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The 7-step process described in this post above using vanilla AutoCad will probably work, but for me, there are somewhere between hundreds and thousands of points that need to be added. So doing them manually one at a time would be too much. This could easily work for smaller projects than mine though.

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@Pointdump wrote:

Erik,
"I am on a quest to draw lines on top of a satellite overlay, in order to export those lines [via DATAEXTRACTION] to use for their GPS coordinates."
I'm curious. What are you going to do with the extracted lines? GPS Routes or Tracks?
Dave

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Essentially. The actual goal of the project is to trace airport geometry (the perimeters of buildings, runways, taxiways, taxiway centerlines, hold short bars, etc). It's a bunch of lines which are exported, manually reformatted (in Sublime Text), and subsequently imported to software used for air traffic control simulations. The airport geometry we have now is heavily outdated, and lacks some important detail that would be easy to add in a click-click-click approach through AutoCad.

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So here's what worked for me:

1. Install AutoCad Map 3D. It seems crazy, but it really is the only way.
2. Run GEOGRAPHICLOCATION command (GEO), from map.
3. Drop marker at 0,0 and elevation 0.
4. Select any worldwide coordinate system, I chose WGS84 PseudoMercator (ESPG:3857). Don't worry about "Unit" or "Drawing Unit".
5. Specify insert location of "0,0,0", and north direction of "90".
6. Stop panicking, it's not supposed to be correct yet.
7. On the bottom toolbar, look for an earth icon with your selected CRS. This appears in AutoCad Map 3D, but not standard AutoCad. Click it, and from the Library, search "CRS:84", and select that CRS (should be ESPG:4326).
8. Go wherever you want and begin generating your tracings. When finished, use DATAEXTRACTION to export the lines' GPS coordinates to a file, and reformat with Sublime Text (or equivalent editor) as necessary to achieve desired result.

I decided to live with keeping these tracings in a separate file, for Map 3D, rather than importing them into my main AutoCad file, which has a ton of other things in it. Since I can't edit it there, and I can still do a dataextraction from directly within Map 3D, I can live with the fact that there are 2 files. Sometimes I want to turn layers on together to compare alignments, and that's not an option here, but I can live with that (and can import if I really needed to check something).

Thanks to all for your time looking into this for me! Bummed it wouldn't work in vanilla AutoCad, but it's quite easy using Map 3D. Maybe I'll import all the AutoCad stuff into the Map 3D file, we'll see. But regardless, I have gotten what I was looking for, so I guess I'm all set! Thanks again!

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[ChicagoLooper]

Seriously? You really want your forum readers to consider this as the solution?  You have to use both Pesudo Mercator EPSG 3857 as well as CRS LL84 EPSG 4326, really? They have to use DATAEXTRACTION then, on top of that, use 'Sublime Text' to reformat? What in the world in Sublime Text and why do you think it's necessary? Whew!! So many hoops to jump through. Why? Watch this video and you'll see it's is entirely possible using Vanilla AutoCAD. (Even easier to use Map 3D the correct way which doesn't use hoops, not the incorrect way as outlined in previous post.)

The only requirements to do this in Vanilla AutoCAD are:

1. The latitude and longitude coordinates, preferably with 6 significant digits. (Given in Post #1 of this thread.)
2. The correct State Plane and Zone (In your case Florida State Plane, East Zone)
3. The x and y coordinates in State Plane that correspond to the your given lat/long.

Note: No. 1 was provided in post #1. No's 2 and 3 can easily be looked up online using free, online tools (I'm sure acquiring 2 and 3 is a lot, lot easier than reformatting using Sublime Text, whatever Sublime Text is.)

To view the video, click >>HERE<.

[trueravenfan]

Yes, seriously, and I don't see how I need to be lectured for that... I marked two solutions to this thread, one of which was yours. Your help remains sincerely appreciated, as it definitively led to getting me what I needed. But again, I was only ever interested in how it could work my way, and have zero interest in how anybody thinks it "should" be done. If it's possible to get the desired result without leaving the simple world of straight lat/lon coordinates (and it is), then it is inherently simpler to take that route rather than translating back and forth with State Plane coordinates the way you describe.

The only oddity of my solution is that EPSG:4326 is not available in the GEOGRAPHICLOCATION menus, and that you must change it after adding the imagery (which baffles me anyway why it isn't an option). Step 3 of your most recent post about getting "coordinates in State Plane that correspond to your lat/lon" is a one-by-one manual task that will not work when I am dealing with thousands of points-- and regardless, I flatly refuse to use the State Plane coordinates approach because its an unnecessary level of abstraction for my particular use case.

The whole point of me using any Autodesk product is to generate and export the coordinates, so yes, the DATAEXTRACTION operation is not only necessary, it's the entire point. From there, I need some simple reformatting and inserting of commas and spaces, "N" and "W", etc, so the ingesting program has the GPS coordinates in the format it desires.

As for "what in the world" Sublime Text is, and "why I think it's necessary", it is a code editor I'm intimately familiar with, which allows multi-selection editing, such that I can reformat thousands of lines simultaneously (in all, the data-extraction-ed text file can be reformatted to my final end product in less than 2 minutes). So certainly way easier than the individual translations to state plane, especially considering that I specifically do not want them to begin with. Instead of doing this in a code editor, I could write a python script or something that does it for me (since it's fairly simple), but it's just as easy to use the multi-selection editing concept, which is illustrated in the example gif of Sublime Text below (Atom/VSCode can also do this):

Nonetheless, the thread is resolved at this point. For anyone who has only a few sets of coordinates, Post #6 will work. If there are too many points for that to be practical, Post #8 is how I was able to get the result I sought.

[ChicagoLooper]

You are misunderstanding how Map 3D works. You can have a drawing where your lines and points have the correct Latitiude/Longitude, and at the same time, while in the same drawing, have the correct Florida State Plane coordinates too. It not an either this or that kind of deal--you don't have to have either/or--both can be correct at the very same time.

WARNING: If you are using CRS:84 your Longitude numbers = your X-coordinates = Eastings are in degrees. Your Latitude numbers = Y-numbers = Northings are in degrees. What does this mean? It means, when you're in AutoCAD  and you need to draw a length, such as a line, or draw an enclosed area, such as a polygon, your numbers are using degrees, not feet! This is a common mistake made by those who do not understand the difference between geographic and projected coordinate systems, the former uses degrees and latter uses feet or meters. CRS:84 is using degrees.

Don't believe me? Go ahead and test it. Set your CoordSys to CRS:84 then draw a circle with 25' diameter (approximately the size of the lighthouse at 938 Whitehead St, in Key West, FL, USA). Place this circle alongside your 'traced' line work. You should also draw an 18' X 9' rectangle, the size of a typical parking stall, next to the 25' diameter circle. How does the circle and rectangle compare with your line work when your CoordSys is set to CRS:84?

[trueravenfan]

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@ChicagoLooper wrote:

You are misunderstanding how Map 3D works.

[...]

WARNING: If you are using CRS:84 your Longitude numbers = your X-coordinates = Eastings are in degrees. Your Latitude numbers = Y-numbers = Northings are in degrees. What does this mean? It means, when you're in AutoCAD  and you need to draw a length, such as a line, or draw an enclosed area, such as a polygon, your numbers are using degrees, not feet! This is a common mistake made by those who do not understand the difference between geographic and projected coordinate systems, the former uses degrees and latter uses feet or meters. CRS:84 is using degrees.

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It is good to point this out more clearly than I had done myself. You're absolutely correct, and I'm not misunderstanding any of that-- in fact, I think the majority of the confusion came from me not being clear enough in the OP.

The intent of the post was exactly as you described (paraphrased): "X coordinates are easting in DEGREES, and Y coordinates northing in DEGREES". I fully understand that this means if I try to draw circles and lines with defined shape/length/etc, the result will be distorted when those coordinates are plotted on a correct projection. For that reason, I do not do any of that-- I realize the limitation of only being able to trace the imagery. Tracing the imagery is my only interest, and since I can do so without translating with state planes, it makes my subsequent work easier.

If anyone intends to draw stuff with intentional lengths, circles, arcs, etc, they will have to use an appropriate projection. I didn't fall in that category and apologize for not making that clear enough in the initial post.