OT ... GIS mapping question

jmp · Jun 17, 2020

How do GIS mapping systems locate buildings that have never been surveyed and are not clearly visible form the all seeing eye in the sky? :scratchchin:

I was looking at my property on the latest upgrade of my counties gis site and see the outline of our 12x12 shed that has never shown up before. It's located directly under a huge beech tree that i'm guessing obscures it even when the foliage is off. Even has the angle in relation to my shop correct. We're well off the road and wooded. Just curious since I haven't found a clear explanation when reading up on it.

Thanks

D Nelson · Jun 17, 2020

Maybe done in the winter while there is no leaves Maybe a type of radar to measure
Don

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MattiJ · Jun 17, 2020

Laser scanning or LIDAR during non-green season?

Laser scanning example:

L Vanice · Jun 17, 2020

jmp said:
How do GIS mapping systems locate buildings that have never been surveyed and are not clearly visible form the all seeing eye in the sky? I was looking at my property on the latest upgrade of my counties gis site and see the outline of our 12x12 shed that has never shown up before. It's located directly under a huge beech tree that i'm guessing obscures it even when the foliage is off. Even has the angle in relation to my shop correct. We're well off the road and wooded. Just curious since I haven't found a clear explanation when reading up on it.

Thanks

Are you paying taxes on the building? My county keeps track of every square foot of concrete patio and walks, in addition to the permanent structures. I had a personal visit once to measure my patio, which had been poured decades earlier by the original builder. Every time a property is sold, it is surveyed.

There was a recent news article about aerial LIDAR surveys of Mexican jungle that detected hidden ancient ruins, but I have the feeling that local assessors would not use that expensive technology.

Larry

DDoug · Jun 17, 2020

L Vanice said:
There was a recent news article about aerial LIDAR surveys of Mexican jungle that detected hidden ancient ruins, but I have the feeling that local assessors would not use that expensive technology.

Larry

Sure they will !
You the taxpayer pays for it, and if it brings in more money (even if not enough to pay for the service) they don't care.

More Money, More Money, More Money ….

jmp · Jun 17, 2020

L Vanice said:
Are you paying taxes on the building? My county keeps track of every square foot of concrete patio and walks, in addition to the permanent structures. I had a personal visit once to measure my patio, which had been poured decades earlier by the original builder. Every time a property is sold, it is surveyed.

There was a recent news article about aerial LIDAR surveys of Mexican jungle that detected hidden ancient ruins, but I have the feeling that local assessors would not use that expensive technology.

Larry

Not a taxed or inspected structure. Just a small building on non permanent foundation that falls well short of the sq ft threshold of needing to be inspected or surveyed. I think from the answers here it's probably LIDAR. Guess you really can't hide from the man.

jmp · Jun 17, 2020

Larry, are you taxed on walks and patios in the county you live in?

john.k · Jun 17, 2020

Our council is broke due to covid..(and lavish spending),wages have to be frozen......but are they freezing costly spy in the sky technology...no way....it generates all kinds of revenue.....All the councils are also using lower flying drone pictures for surveillance ,which integrate with all other spy measures including street view.........These scum are the robber barons and we are the serfs.

D Bronson · Jun 17, 2020

jmp:

The GIS mapping is done using aerial stereo photogrammetry. The flights are done in the spring before the trees leaf out. (It's not usually done in the winter since any snow obscures the ground.) Your shed either wasn't noticed on the previous photographs or was built since the last flight. A search of wikipedia on the subject will turn up more info - or if you want to dig deeper ASPRS.org is the organization that supports the people that do this kind of work.

By the way, driving around you may have noticed 5' white crosses painted on the road. These are the ground control points that the mappers use calibrate the aerial photos. The crosses are located by surveyors and tied back to known control points.

I don't believe anyone is using lidar for typical county gis work.

Regards,

DB

L Vanice · Jun 17, 2020

jmp said:
Larry, are you taxed on walks and patios in the county you live in?

Yes, the assessed property value adds up the land and all improvements, including concrete features. I think stone and blacktop drives are not taxed because they are not considered permanent.

Larry

MattiJ · Jun 17, 2020

D Bronson said:
I don't believe anyone is using lidar for typical county gis work.

Regards,

DB

They do at least in here. It was on the news some time ago that they finished laser scanning the whole country and next round is starting soon. Smaller areas have been laser scanned even lot earlier.

JST · Jun 17, 2020

I've had this evil thought about those eye in the sky surveys.

If I knew when the flights would be made, I'd lay out a blue tarp and some white ones around it. When the county wanted to tax me on the "swimming pool", I'd tell them they are crazy, I do not have one (true). When they insisted, I'd eventually let them look for it themselves, after letting them stew for a bit.

Just goes to show that being French, Swedish and Irish is a bad combination....... An inherent dislike of authority combined with being stubborn, and liking a good fight.

EPAIII · Jun 18, 2020

I thought those white crosses were painted in the night by Russian spies so their ICBMs could be more accurate.

D Bronson said:
jmp:

The GIS mapping is done using aerial stereo photogrammetry. The flights are done in the spring before the trees leaf out. (It's not usually done in the winter since any snow obscures the ground.) Your shed either wasn't noticed on the previous photographs or was built since the last flight. A search of wikipedia on the subject will turn up more info - or if you want to dig deeper ASPRS.org is the organization that supports the people that do this kind of work.

By the way, driving around you may have noticed 5' white crosses painted on the road. These are the ground control points that the mappers use calibrate the aerial photos. The crosses are located by surveyors and tied back to known control points.

I don't believe anyone is using lidar for typical county gis work.

Regards,

DB

DDoug · Jun 18, 2020

JST said:
I've had this evil thought about those eye in the sky surveys.

If I knew when the flights would be made, I'd lay out a blue tarp and some white ones around it. When the county wanted to tax me on the "swimming pool", I'd tell them they are crazy, I do not have one (true). When they insisted, I'd eventually let them look for it themselves, after letting them stew for a bit.

Just goes to show that being French, Swedish and Irish is a bad combination....... An inherent dislike of authority combined with being stubborn, and liking a good fight.

Or post a message "Worldwide" using a lawnmower...…

john.k · Jun 18, 2020

JST ,if they think you ve got a swimming pool ,they will add the assessment to your taxes ......and very likely include a $1000 penalty because you dont have a compliant child proof fence around it.

DDoug · Jun 18, 2020

john.k said:
JST ,if they think you ve got a swimming pool ,they will add the assessment to your taxes ......and very likely include a $1000 penalty because you dont have a compliant child proof fence around it.

I think the idea is to show how flawed the local taxing body's system is....

Add some inner tubes and a raft for effect.

gustafson · Jun 18, 2020

digger doug said:
Or post a message "Worldwide" using a lawnmower...…

Or a copyright symbol

ought to drive someone crazy

DDoug · Jun 18, 2020

gustafson said:
Or a copyright symbol

ought to drive someone crazy

Can you program/hack one of those "Roomba mowers" to doo artwork ?

cameraman · Jun 18, 2020

D Bronson said:
jmp:

The GIS mapping is done using aerial stereo photogrammetry. The flights are done in the spring before the trees leaf out. (It's not usually done in the winter since any snow obscures the ground.) Your shed either wasn't noticed on the previous photographs or was built since the last flight. A search of wikipedia on the subject will turn up more info - or if you want to dig deeper ASPRS.org is the organization that supports the people that do this kind of work.

By the way, driving around you may have noticed 5' white crosses painted on the road. These are the ground control points that the mappers use calibrate the aerial photos. The crosses are located by surveyors and tied back to known control points.

I don't believe anyone is using lidar for typical county gis work.

Regards,

DB

I'm totally shocked that anyone here knows what aerial photogrammetry is / stereo photogrammetry.

Been a member of the ASPRS for decades (now).

Cheers,

Eric

_______________________________________________________________________________________

As far as detecting Mayan sites through the tree canopy a version of SAR (Synthetic Aperture Radar) has a ground penetrating effect possibly to one or two meters.

Also has been used to detect / bust drug operations,

Same technique SAR was used to map Venus as the atmosphere is so thick / impenetrable to UV, IR and visible light. Got to meet the guy (Dr. Charles Elachi) at JPL (Pasadena) that designed that system.

There was an air flyable version of the SAR system to test before they put it on a space craft and sent it to the planet Venus.

Several interesting fly-bys that also 'Happened" to intersect various south American jungle sites.

JST · Jun 18, 2020

digger doug said:
I think the idea is to show how flawed the local taxing body's system is....

Add some inner tubes and a raft for effect.

Excellent idea.

Add taxes and fines? I'll pay up if they can show me where the pool is in my yard.

True story just this spring: Local town sent us all trash service bills way late (after due date). And then added a fee because we all PAID late.

OT ... GIS mapping question

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